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crypto/internal/mlkem768: move to crypto/internal/fips/mlkem

Browse Source 
In the process, replace out-of-module imports with their FIPS versions.

For #69536

Change-Id: I83e900b7c38ecf760382e5dca7fd0b1eaa5a5589
Reviewed-on: https://go-review.googlesource.com/c/go/+/626879
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
This commit is contained in:
yuhan6665 2025-05-04 21:47:49 -04:00
parent f63b058d4a
commit 3833e8e2cb
14 changed files with 1703 additions and 902 deletions
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148
aes/ctr.go Normal file
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@ -0,0 +1,148 @@
// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package aes
import (
//"crypto/internal/fips140"
"github.com/xtls/reality/alias"
"github.com/xtls/reality/subtle"
"github.com/xtls/reality/byteorder"
"math/bits"
)
type CTR struct {
b Block
ivlo, ivhi uint64 // start counter as 64-bit limbs
offset uint64 // for XORKeyStream only
}
func NewCTR(b *Block, iv []byte) *CTR {
// Allocate the CTR here, in an easily inlineable function, so
// the allocation can be done in the caller's stack frame
// instead of the heap. See issue 70499.
c := newCTR(b, iv)
return &c
}
func newCTR(b *Block, iv []byte) CTR {
if len(iv) != BlockSize {
panic("bad IV length")
}
return CTR{
b: *b,
ivlo: byteorder.BEUint64(iv[8:16]),
ivhi: byteorder.BEUint64(iv[0:8]),
offset: 0,
}
}
func (c *CTR) XORKeyStream(dst, src []byte) {
c.XORKeyStreamAt(dst, src, c.offset)
var carry uint64
c.offset, carry = bits.Add64(c.offset, uint64(len(src)), 0)
if carry != 0 {
panic("crypto/aes: counter overflow")
}
}
// RoundToBlock is used by CTR_DRBG, which discards the rightmost unused bits at
// each request. It rounds the offset up to the next block boundary.
func RoundToBlock(c *CTR) {
if remainder := c.offset % BlockSize; remainder != 0 {
var carry uint64
c.offset, carry = bits.Add64(c.offset, BlockSize-remainder, 0)
if carry != 0 {
panic("crypto/aes: counter overflow")
}
}
}
// XORKeyStreamAt behaves like XORKeyStream but keeps no state, and instead
// seeks into the keystream by the given bytes offset from the start (ignoring
// any XORKetStream calls). This allows for random access into the keystream, up
// to 16 EiB from the start.
func (c *CTR) XORKeyStreamAt(dst, src []byte, offset uint64) {
if len(dst) < len(src) {
panic("crypto/aes: len(dst) < len(src)")
}
dst = dst[:len(src)]
if alias.InexactOverlap(dst, src) {
panic("crypto/aes: invalid buffer overlap")
}
//fips140.RecordApproved()
ivlo, ivhi := add128(c.ivlo, c.ivhi, offset/BlockSize)
if blockOffset := offset % BlockSize; blockOffset != 0 {
// We have a partial block at the beginning.
var in, out [BlockSize]byte
copy(in[blockOffset:], src)
ctrBlocks1(&c.b, &out, &in, ivlo, ivhi)
n := copy(dst, out[blockOffset:])
src = src[n:]
dst = dst[n:]
ivlo, ivhi = add128(ivlo, ivhi, 1)
}
for len(src) >= 8*BlockSize {
ctrBlocks8(&c.b, (*[8 * BlockSize]byte)(dst), (*[8 * BlockSize]byte)(src), ivlo, ivhi)
src = src[8*BlockSize:]
dst = dst[8*BlockSize:]
ivlo, ivhi = add128(ivlo, ivhi, 8)
}
// The tail can have at most 7 = 4 + 2 + 1 blocks.
if len(src) >= 4*BlockSize {
ctrBlocks4(&c.b, (*[4 * BlockSize]byte)(dst), (*[4 * BlockSize]byte)(src), ivlo, ivhi)
src = src[4*BlockSize:]
dst = dst[4*BlockSize:]
ivlo, ivhi = add128(ivlo, ivhi, 4)
}
if len(src) >= 2*BlockSize {
ctrBlocks2(&c.b, (*[2 * BlockSize]byte)(dst), (*[2 * BlockSize]byte)(src), ivlo, ivhi)
src = src[2*BlockSize:]
dst = dst[2*BlockSize:]
ivlo, ivhi = add128(ivlo, ivhi, 2)
}
if len(src) >= 1*BlockSize {
ctrBlocks1(&c.b, (*[1 * BlockSize]byte)(dst), (*[1 * BlockSize]byte)(src), ivlo, ivhi)
src = src[1*BlockSize:]
dst = dst[1*BlockSize:]
ivlo, ivhi = add128(ivlo, ivhi, 1)
}
if len(src) != 0 {
// We have a partial block at the end.
var in, out [BlockSize]byte
copy(in[:], src)
ctrBlocks1(&c.b, &out, &in, ivlo, ivhi)
copy(dst, out[:])
}
}
// Each ctrBlocksN function XORs src with N blocks of counter keystream, and
// stores it in dst. src is loaded in full before storing dst, so they can
// overlap even inexactly. The starting counter value is passed in as a pair of
// little-endian 64-bit integers.
func ctrBlocks(b *Block, dst, src []byte, ivlo, ivhi uint64) {
buf := make([]byte, len(src), 8*BlockSize)
for i := 0; i < len(buf); i += BlockSize {
byteorder.BEPutUint64(buf[i:], ivhi)
byteorder.BEPutUint64(buf[i+8:], ivlo)
ivlo, ivhi = add128(ivlo, ivhi, 1)
encryptBlock(b, buf[i:], buf[i:])
}
// XOR into buf first, in case src and dst overlap (see above).
subtle.XORBytes(buf, src, buf)
copy(dst, buf)
}
func add128(lo, hi uint64, x uint64) (uint64, uint64) {
lo, c := bits.Add64(lo, x, 0)
hi, _ = bits.Add64(hi, 0, c)
return lo, hi
}

21
aes/ctr_noasm.go Normal file
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@ -0,0 +1,21 @@
// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package aes
func ctrBlocks1(b *Block, dst, src *[BlockSize]byte, ivlo, ivhi uint64) {
ctrBlocks(b, dst[:], src[:], ivlo, ivhi)
}
func ctrBlocks2(b *Block, dst, src *[2 * BlockSize]byte, ivlo, ivhi uint64) {
ctrBlocks(b, dst[:], src[:], ivlo, ivhi)
}
func ctrBlocks4(b *Block, dst, src *[4 * BlockSize]byte, ivlo, ivhi uint64) {
ctrBlocks(b, dst[:], src[:], ivlo, ivhi)
}
func ctrBlocks8(b *Block, dst, src *[8 * BlockSize]byte, ivlo, ivhi uint64) {
ctrBlocks(b, dst[:], src[:], ivlo, ivhi)
}

143
drbg/ctrdrbg.go Normal file
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@ -0,0 +1,143 @@
// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package drbg
import (
//"crypto/internal/fips140"
"github.com/xtls/reality/aes"
"github.com/xtls/reality/subtle"
"github.com/xtls/reality/byteorder"
"math/bits"
)
// Counter is an SP 800-90A Rev. 1 CTR_DRBG instantiated with AES-256.
//
// Per Table 3, it has a security strength of 256 bits, a seed size of 384 bits,
// a counter length of 128 bits, a reseed interval of 2^48 requests, and a
// maximum request size of 2^19 bits (2^16 bytes, 64 KiB).
//
// We support a narrow range of parameters that fit the needs of our RNG:
// AES-256, no derivation function, no personalization string, no prediction
// resistance, and 384-bit additional input.
//
// WARNING: this type provides tightly scoped support for the DRBG
// functionality we need for FIPS 140-3 _only_. This type _should not_ be used
// outside of the FIPS 140-3 module for any other use.
//
// In particular, as documented, Counter does not support the derivation
// function, or personalization strings which are necessary for safely using
// this DRBG for generic purposes without leaking sensitive values.
type Counter struct {
// c is instantiated with K as the key and V as the counter.
c aes.CTR
reseedCounter uint64
}
const (
keySize = 256 / 8
SeedSize = keySize + aes.BlockSize
reseedInterval = 1 << 48
maxRequestSize = (1 << 19) / 8
)
func NewCounter(entropy *[SeedSize]byte) *Counter {
// CTR_DRBG_Instantiate_algorithm, per Section 10.2.1.3.1.
//fips140.RecordApproved()
K := make([]byte, keySize)
V := make([]byte, aes.BlockSize)
// V starts at 0, but is incremented in CTR_DRBG_Update before each use,
// unlike AES-CTR where it is incremented after each use.
V[len(V)-1] = 1
cipher, err := aes.New(K)
if err != nil {
panic(err)
}
c := &Counter{}
c.c = *aes.NewCTR(cipher, V)
c.update(entropy)
c.reseedCounter = 1
return c
}
func (c *Counter) update(seed *[SeedSize]byte) {
// CTR_DRBG_Update, per Section 10.2.1.2.
temp := make([]byte, SeedSize)
c.c.XORKeyStream(temp, seed[:])
K := temp[:keySize]
V := temp[keySize:]
// Again, we pre-increment V, like in NewCounter.
increment((*[aes.BlockSize]byte)(V))
cipher, err := aes.New(K)
if err != nil {
panic(err)
}
c.c = *aes.NewCTR(cipher, V)
}
func increment(v *[aes.BlockSize]byte) {
hi := byteorder.BEUint64(v[:8])
lo := byteorder.BEUint64(v[8:])
lo, c := bits.Add64(lo, 1, 0)
hi, _ = bits.Add64(hi, 0, c)
byteorder.BEPutUint64(v[:8], hi)
byteorder.BEPutUint64(v[8:], lo)
}
func (c *Counter) Reseed(entropy, additionalInput *[SeedSize]byte) {
// CTR_DRBG_Reseed_algorithm, per Section 10.2.1.4.1.
//fips140.RecordApproved()
var seed [SeedSize]byte
subtle.XORBytes(seed[:], entropy[:], additionalInput[:])
c.update(&seed)
c.reseedCounter = 1
}
// Generate produces at most maxRequestSize bytes of random data in out.
func (c *Counter) Generate(out []byte, additionalInput *[SeedSize]byte) (reseedRequired bool) {
// CTR_DRBG_Generate_algorithm, per Section 10.2.1.5.1.
//fips140.RecordApproved()
if len(out) > maxRequestSize {
panic("crypto/drbg: internal error: request size exceeds maximum")
}
// Step 1.
if c.reseedCounter > reseedInterval {
return true
}
// Step 2.
if additionalInput != nil {
c.update(additionalInput)
} else {
// If the additional input is null, the first CTR_DRBG_Update is
// skipped, but the additional input is replaced with an all-zero string
// for the second CTR_DRBG_Update.
additionalInput = new([SeedSize]byte)
}
// Steps 3-5.
clear(out)
c.c.XORKeyStream(out, out)
aes.RoundToBlock(&c.c)
// Step 6.
c.update(additionalInput)
// Step 7.
c.reseedCounter++
// Step 8.
return false
}

102
drbg/rand.go Normal file
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@ -0,0 +1,102 @@
// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package drbg provides cryptographically secure random bytes
// usable by FIPS code. In FIPS mode it uses an SP 800-90A Rev. 1
// Deterministic Random Bit Generator (DRBG). Otherwise,
// it uses the operating system's random number generator.
package drbg
import (
"github.com/xtls/reality/entropy"
// "crypto/internal/fips140"
"github.com/xtls/reality/randutil"
// "github.com/xtls/reality/sysrand"
"crypto/rand"
"io"
"sync"
)
var drbgs = sync.Pool{
New: func() any {
var c *Counter
entropy.Depleted(func(seed *[48]byte) {
c = NewCounter(seed)
})
return c
},
}
// Read fills b with cryptographically secure random bytes. In FIPS mode, it
// uses an SP 800-90A Rev. 1 Deterministic Random Bit Generator (DRBG).
// Otherwise, it uses the operating system's random number generator.
func Read(b []byte) {
// if !fips140.Enabled {
// rand.Read(b)
// return
// }
// At every read, 128 random bits from the operating system are mixed as
// additional input, to make the output as strong as non-FIPS randomness.
// This is not credited as entropy for FIPS purposes, as allowed by Section
// 8.7.2: "Note that a DRBG does not rely on additional input to provide
// entropy, even though entropy could be provided in the additional input".
additionalInput := new([SeedSize]byte)
rand.Read(additionalInput[:16])
drbg := drbgs.Get().(*Counter)
defer drbgs.Put(drbg)
for len(b) > 0 {
size := min(len(b), maxRequestSize)
if reseedRequired := drbg.Generate(b[:size], additionalInput); reseedRequired {
// See SP 800-90A Rev. 1, Section 9.3.1, Steps 6-8, as explained in
// Section 9.3.2: if Generate reports a reseed is required, the
// additional input is passed to Reseed along with the entropy and
// then nulled before the next Generate call.
entropy.Depleted(func(seed *[48]byte) {
drbg.Reseed(seed, additionalInput)
})
additionalInput = nil
continue
}
b = b[size:]
}
}
// DefaultReader is a sentinel type, embedded in the default
// [crypto/rand.Reader], used to recognize it when passed to
// APIs that accept a rand io.Reader.
type DefaultReader interface{ defaultReader() }
// ReadWithReader uses Reader to fill b with cryptographically secure random
// bytes. It is intended for use in APIs that expose a rand io.Reader.
//
// If Reader is not the default Reader from crypto/rand,
// [randutil.MaybeReadByte] and [fips140.RecordNonApproved] are called.
func ReadWithReader(r io.Reader, b []byte) error {
if _, ok := r.(DefaultReader); ok {
Read(b)
return nil
}
//fips140.RecordNonApproved()
randutil.MaybeReadByte(r)
_, err := io.ReadFull(r, b)
return err
}
// ReadWithReaderDeterministic is like ReadWithReader, but it doesn't call
// [randutil.MaybeReadByte] on non-default Readers.
func ReadWithReaderDeterministic(r io.Reader, b []byte) error {
if _, ok := r.(DefaultReader); ok {
Read(b)
return nil
}
//fips140.RecordNonApproved()
_, err := io.ReadFull(r, b)
return err
}

29
entropy/entropy.go Normal file
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@ -0,0 +1,29 @@
// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package entropy provides the passive entropy source for the FIPS 140-3
// module. It is only used in FIPS mode by [crypto/internal/fips140/drbg.Read].
//
// This complies with IG 9.3.A, Additional Comment 12, which until January 1,
// 2026 allows new modules to meet an [earlier version] of Resolution 2(b):
// "A software module that contains an approved DRBG that receives a LOAD
// command (or its logical equivalent) with entropy obtained from [...] inside
// the physical perimeter of the operational environment of the module [...]."
//
// Distributions that have their own SP 800-90B entropy source should replace
// this package with their own implementation.
//
// [earlier version]: https://csrc.nist.gov/CSRC/media/Projects/cryptographic-module-validation-program/documents/IG%209.3.A%20Resolution%202b%5BMarch%2026%202024%5D.pdf
package entropy
// "github.com/xtls/reality/sysrand"
import "crypto/rand"
// Depleted notifies the entropy source that the entropy in the module is
// "depleted" and provides the callback for the LOAD command.
func Depleted(LOAD func(*[48]byte)) {
var entropy [48]byte
rand.Read(entropy[:])
LOAD(&entropy)
}

6
handshake_client.go
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@ -23,7 +23,7 @@ import (
"time"
"github.com/xtls/reality/hpke"
"github.com/xtls/reality/mlkem768"
"github.com/xtls/reality/mlkem"
"github.com/xtls/reality/tls13"
)
@ -160,11 +160,11 @@ func (c *Conn) makeClientHello() (*clientHelloMsg, *keySharePrivateKeys, *echCon
if err != nil {
return nil, nil, nil, err
}
seed := make([]byte, mlkem768.SeedSize)
seed := make([]byte, mlkem.SeedSize)
if _, err := io.ReadFull(config.rand(), seed); err != nil {
return nil, nil, nil, err
}
keyShareKeys.kyber, err = mlkem768.NewDecapsulationKey768(seed)
keyShareKeys.kyber, err = mlkem.NewDecapsulationKey768(seed)
if err != nil {
return nil, nil, nil, err
}

4
handshake_client_tls13.go
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@ -16,7 +16,7 @@ import (
"slices"
"time"
"github.com/xtls/reality/mlkem768"
"github.com/xtls/reality/mlkem"
"github.com/xtls/reality/tls13"
"golang.org/x/crypto/hkdf"
)
@ -481,7 +481,7 @@ func (hs *clientHandshakeStateTLS13) establishHandshakeKeys() error {
ecdhePeerData := hs.serverHello.serverShare.data
if hs.serverHello.serverShare.group == x25519Kyber768Draft00 {
if len(ecdhePeerData) != x25519PublicKeySize+mlkem768.CiphertextSize768 {
if len(ecdhePeerData) != x25519PublicKeySize+mlkem.CiphertextSize768 {
c.sendAlert(alertIllegalParameter)
return errors.New("tls: invalid server key share")
}

4
handshake_server_tls13.go
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@ -22,7 +22,7 @@ import (
"slices"
"time"
"github.com/xtls/reality/mlkem768"
"github.com/xtls/reality/mlkem"
"github.com/xtls/reality/tls13"
)
@ -276,7 +276,7 @@ func (hs *serverHandshakeStateTLS13) processClientHello() error {
ecdhData := clientKeyShare.data
if selectedGroup == x25519Kyber768Draft00 {
ecdhGroup = X25519
if len(ecdhData) != x25519PublicKeySize+mlkem768.EncapsulationKeySize768 {
if len(ecdhData) != x25519PublicKeySize+mlkem.EncapsulationKeySize768 {
c.sendAlert(alertIllegalParameter)
return errors.New("tls: invalid Kyber client key share")
}

18
key_schedule.go
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@ -11,9 +11,8 @@ import (
"hash"
"io"
"golang.org/x/crypto/sha3"
"github.com/xtls/reality/mlkem768"
"github.com/xtls/reality/mlkem"
"github.com/xtls/reality/sha3"
"github.com/xtls/reality/tls13"
)
@ -55,11 +54,11 @@ func (c *cipherSuiteTLS13) exportKeyingMaterial(s *tls13.MasterSecret, transcrip
type keySharePrivateKeys struct {
curveID CurveID
ecdhe *ecdh.PrivateKey
kyber *mlkem768.DecapsulationKey768
kyber *mlkem.DecapsulationKey768
}
// kyberDecapsulate implements decapsulation according to Kyber Round 3.
func kyberDecapsulate(dk *mlkem768.DecapsulationKey768, c []byte) ([]byte, error) {
func kyberDecapsulate(dk *mlkem.DecapsulationKey768, c []byte) ([]byte, error) {
K, err := dk.Decapsulate(c)
if err != nil {
return nil, err
@ -69,7 +68,7 @@ func kyberDecapsulate(dk *mlkem768.DecapsulationKey768, c []byte) ([]byte, error
// kyberEncapsulate implements encapsulation according to Kyber Round 3.
func kyberEncapsulate(ek []byte) (c, ss []byte, err error) {
k, err := mlkem768.NewEncapsulationKey768(ek)
k, err := mlkem.NewEncapsulationKey768(ek)
if err != nil {
return nil, nil, err
}
@ -78,13 +77,14 @@ func kyberEncapsulate(ek []byte) (c, ss []byte, err error) {
}
func kyberSharedSecret(c, K []byte) []byte {
// Package mlkem768 implements ML-KEM, which compared to Kyber removed a
// Package mlkem implements ML-KEM, which compared to Kyber removed a
// final hashing step. Compute SHAKE-256(K || SHA3-256(c), 32) to match Kyber.
// See https://words.filippo.io/mlkem768/#bonus-track-using-a-ml-kem-implementation-as-kyber-v3.
h := sha3.NewShake256()
h.Write(K)
ch := sha3.Sum256(c)
h.Write(ch[:])
ch := sha3.New256()
ch.Write(c)
h.Write(ch.Sum(nil))
out := make([]byte, 32)
h.Read(out)
return out

550
mlkem/field.go Normal file
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@ -0,0 +1,550 @@
// Copyright 2024 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package mlkem
import (
"github.com/xtls/reality/sha3"
"github.com/xtls/reality/byteorder"
"errors"
)
// fieldElement is an integer modulo q, an element of ℤ_q. It is always reduced.
type fieldElement uint16
// fieldCheckReduced checks that a value a is < q.
func fieldCheckReduced(a uint16) (fieldElement, error) {
if a >= q {
return 0, errors.New("unreduced field element")
}
return fieldElement(a), nil
}
// fieldReduceOnce reduces a value a < 2q.
func fieldReduceOnce(a uint16) fieldElement {
x := a - q
// If x underflowed, then x >= 2¹⁶ - q > 2¹⁵, so the top bit is set.
x += (x >> 15) * q
return fieldElement(x)
}
func fieldAdd(a, b fieldElement) fieldElement {
x := uint16(a + b)
return fieldReduceOnce(x)
}
func fieldSub(a, b fieldElement) fieldElement {
x := uint16(a - b + q)
return fieldReduceOnce(x)
}
const (
barrettMultiplier = 5039 // 2¹² * 2¹² / q
barrettShift = 24 // log₂(2¹² * 2¹²)
)
// fieldReduce reduces a value a < 2q² using Barrett reduction, to avoid
// potentially variable-time division.
func fieldReduce(a uint32) fieldElement {
quotient := uint32((uint64(a) * barrettMultiplier) >> barrettShift)
return fieldReduceOnce(uint16(a - quotient*q))
}
func fieldMul(a, b fieldElement) fieldElement {
x := uint32(a) * uint32(b)
return fieldReduce(x)
}
// fieldMulSub returns a * (b - c). This operation is fused to save a
// fieldReduceOnce after the subtraction.
func fieldMulSub(a, b, c fieldElement) fieldElement {
x := uint32(a) * uint32(b-c+q)
return fieldReduce(x)
}
// fieldAddMul returns a * b + c * d. This operation is fused to save a
// fieldReduceOnce and a fieldReduce.
func fieldAddMul(a, b, c, d fieldElement) fieldElement {
x := uint32(a) * uint32(b)
x += uint32(c) * uint32(d)
return fieldReduce(x)
}
// compress maps a field element uniformly to the range 0 to 2ᵈ-1, according to
// FIPS 203, Definition 4.7.
func compress(x fieldElement, d uint8) uint16 {
// We want to compute (x * 2ᵈ) / q, rounded to nearest integer, with 1/2
// rounding up (see FIPS 203, Section 2.3).
// Barrett reduction produces a quotient and a remainder in the range [0, 2q),
// such that dividend = quotient * q + remainder.
dividend := uint32(x) << d // x * 2ᵈ
quotient := uint32(uint64(dividend) * barrettMultiplier >> barrettShift)
remainder := dividend - quotient*q
// Since the remainder is in the range [0, 2q), not [0, q), we need to
// portion it into three spans for rounding.
//
// [ 0, q/2 ) -> round to 0
// [ q/2, q + q/2 ) -> round to 1
// [ q + q/2, 2q ) -> round to 2
//
// We can convert that to the following logic: add 1 if remainder > q/2,
// then add 1 again if remainder > q + q/2.
//
// Note that if remainder > x, then ⌊x⌋ - remainder underflows, and the top
// bit of the difference will be set.
quotient += (q/2 - remainder) >> 31 & 1
quotient += (q + q/2 - remainder) >> 31 & 1
// quotient might have overflowed at this point, so reduce it by masking.
var mask uint32 = (1 << d) - 1
return uint16(quotient & mask)
}
// decompress maps a number x between 0 and 2ᵈ-1 uniformly to the full range of
// field elements, according to FIPS 203, Definition 4.8.
func decompress(y uint16, d uint8) fieldElement {
// We want to compute (y * q) / 2ᵈ, rounded to nearest integer, with 1/2
// rounding up (see FIPS 203, Section 2.3).
dividend := uint32(y) * q
quotient := dividend >> d // (y * q) / 2ᵈ
// The d'th least-significant bit of the dividend (the most significant bit
// of the remainder) is 1 for the top half of the values that divide to the
// same quotient, which are the ones that round up.
quotient += dividend >> (d - 1) & 1
// quotient is at most (2¹¹-1) * q / 2¹¹ + 1 = 3328, so it didn't overflow.
return fieldElement(quotient)
}
// ringElement is a polynomial, an element of R_q, represented as an array
// according to FIPS 203, Section 2.4.4.
type ringElement [n]fieldElement
// polyAdd adds two ringElements or nttElements.
func polyAdd[T ~[n]fieldElement](a, b T) (s T) {
for i := range s {
s[i] = fieldAdd(a[i], b[i])
}
return s
}
// polySub subtracts two ringElements or nttElements.
func polySub[T ~[n]fieldElement](a, b T) (s T) {
for i := range s {
s[i] = fieldSub(a[i], b[i])
}
return s
}
// polyByteEncode appends the 384-byte encoding of f to b.
//
// It implements ByteEncode₁₂, according to FIPS 203, Algorithm 5.
func polyByteEncode[T ~[n]fieldElement](b []byte, f T) []byte {
out, B := sliceForAppend(b, encodingSize12)
for i := 0; i < n; i += 2 {
x := uint32(f[i]) | uint32(f[i+1])<<12
B[0] = uint8(x)
B[1] = uint8(x >> 8)
B[2] = uint8(x >> 16)
B = B[3:]
}
return out
}
// polyByteDecode decodes the 384-byte encoding of a polynomial, checking that
// all the coefficients are properly reduced. This fulfills the "Modulus check"
// step of ML-KEM Encapsulation.
//
// It implements ByteDecode₁₂, according to FIPS 203, Algorithm 6.
func polyByteDecode[T ~[n]fieldElement](b []byte) (T, error) {
if len(b) != encodingSize12 {
return T{}, errors.New("mlkem: invalid encoding length")
}
var f T
for i := 0; i < n; i += 2 {
d := uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16
const mask12 = 0b1111_1111_1111
var err error
if f[i], err = fieldCheckReduced(uint16(d & mask12)); err != nil {
return T{}, errors.New("mlkem: invalid polynomial encoding")
}
if f[i+1], err = fieldCheckReduced(uint16(d >> 12)); err != nil {
return T{}, errors.New("mlkem: invalid polynomial encoding")
}
b = b[3:]
}
return f, nil
}
// sliceForAppend takes a slice and a requested number of bytes. It returns a
// slice with the contents of the given slice followed by that many bytes and a
// second slice that aliases into it and contains only the extra bytes. If the
// original slice has sufficient capacity then no allocation is performed.
func sliceForAppend(in []byte, n int) (head, tail []byte) {
if total := len(in) + n; cap(in) >= total {
head = in[:total]
} else {
head = make([]byte, total)
copy(head, in)
}
tail = head[len(in):]
return
}
// ringCompressAndEncode1 appends a 32-byte encoding of a ring element to s,
// compressing one coefficients per bit.
//
// It implements Compress₁, according to FIPS 203, Definition 4.7,
// followed by ByteEncode₁, according to FIPS 203, Algorithm 5.
func ringCompressAndEncode1(s []byte, f ringElement) []byte {
s, b := sliceForAppend(s, encodingSize1)
for i := range b {
b[i] = 0
}
for i := range f {
b[i/8] |= uint8(compress(f[i], 1) << (i % 8))
}
return s
}
// ringDecodeAndDecompress1 decodes a 32-byte slice to a ring element where each
// bit is mapped to 0 or ⌈q/2⌋.
//
// It implements ByteDecode₁, according to FIPS 203, Algorithm 6,
// followed by Decompress₁, according to FIPS 203, Definition 4.8.
func ringDecodeAndDecompress1(b *[encodingSize1]byte) ringElement {
var f ringElement
for i := range f {
b_i := b[i/8] >> (i % 8) & 1
const halfQ = (q + 1) / 2 // ⌈q/2⌋, rounded up per FIPS 203, Section 2.3
f[i] = fieldElement(b_i) * halfQ // 0 decompresses to 0, and 1 to ⌈q/2⌋
}
return f
}
// ringCompressAndEncode4 appends a 128-byte encoding of a ring element to s,
// compressing two coefficients per byte.
//
// It implements Compress₄, according to FIPS 203, Definition 4.7,
// followed by ByteEncode₄, according to FIPS 203, Algorithm 5.
func ringCompressAndEncode4(s []byte, f ringElement) []byte {
s, b := sliceForAppend(s, encodingSize4)
for i := 0; i < n; i += 2 {
b[i/2] = uint8(compress(f[i], 4) | compress(f[i+1], 4)<<4)
}
return s
}
// ringDecodeAndDecompress4 decodes a 128-byte encoding of a ring element where
// each four bits are mapped to an equidistant distribution.
//
// It implements ByteDecode₄, according to FIPS 203, Algorithm 6,
// followed by Decompress₄, according to FIPS 203, Definition 4.8.
func ringDecodeAndDecompress4(b *[encodingSize4]byte) ringElement {
var f ringElement
for i := 0; i < n; i += 2 {
f[i] = fieldElement(decompress(uint16(b[i/2]&0b1111), 4))
f[i+1] = fieldElement(decompress(uint16(b[i/2]>>4), 4))
}
return f
}
// ringCompressAndEncode10 appends a 320-byte encoding of a ring element to s,
// compressing four coefficients per five bytes.
//
// It implements Compress₁₀, according to FIPS 203, Definition 4.7,
// followed by ByteEncode₁₀, according to FIPS 203, Algorithm 5.
func ringCompressAndEncode10(s []byte, f ringElement) []byte {
s, b := sliceForAppend(s, encodingSize10)
for i := 0; i < n; i += 4 {
var x uint64
x |= uint64(compress(f[i], 10))
x |= uint64(compress(f[i+1], 10)) << 10
x |= uint64(compress(f[i+2], 10)) << 20
x |= uint64(compress(f[i+3], 10)) << 30
b[0] = uint8(x)
b[1] = uint8(x >> 8)
b[2] = uint8(x >> 16)
b[3] = uint8(x >> 24)
b[4] = uint8(x >> 32)
b = b[5:]
}
return s
}
// ringDecodeAndDecompress10 decodes a 320-byte encoding of a ring element where
// each ten bits are mapped to an equidistant distribution.
//
// It implements ByteDecode₁₀, according to FIPS 203, Algorithm 6,
// followed by Decompress₁₀, according to FIPS 203, Definition 4.8.
func ringDecodeAndDecompress10(bb *[encodingSize10]byte) ringElement {
b := bb[:]
var f ringElement
for i := 0; i < n; i += 4 {
x := uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 | uint64(b[4])<<32
b = b[5:]
f[i] = fieldElement(decompress(uint16(x>>0&0b11_1111_1111), 10))
f[i+1] = fieldElement(decompress(uint16(x>>10&0b11_1111_1111), 10))
f[i+2] = fieldElement(decompress(uint16(x>>20&0b11_1111_1111), 10))
f[i+3] = fieldElement(decompress(uint16(x>>30&0b11_1111_1111), 10))
}
return f
}
// ringCompressAndEncode appends an encoding of a ring element to s,
// compressing each coefficient to d bits.
//
// It implements Compress, according to FIPS 203, Definition 4.7,
// followed by ByteEncode, according to FIPS 203, Algorithm 5.
func ringCompressAndEncode(s []byte, f ringElement, d uint8) []byte {
var b byte
var bIdx uint8
for i := 0; i < n; i++ {
c := compress(f[i], d)
var cIdx uint8
for cIdx < d {
b |= byte(c>>cIdx) << bIdx
bits := min(8-bIdx, d-cIdx)
bIdx += bits
cIdx += bits
if bIdx == 8 {
s = append(s, b)
b = 0
bIdx = 0
}
}
}
if bIdx != 0 {
panic("mlkem: internal error: bitsFilled != 0")
}
return s
}
// ringDecodeAndDecompress decodes an encoding of a ring element where
// each d bits are mapped to an equidistant distribution.
//
// It implements ByteDecode, according to FIPS 203, Algorithm 6,
// followed by Decompress, according to FIPS 203, Definition 4.8.
func ringDecodeAndDecompress(b []byte, d uint8) ringElement {
var f ringElement
var bIdx uint8
for i := 0; i < n; i++ {
var c uint16
var cIdx uint8
for cIdx < d {
c |= uint16(b[0]>>bIdx) << cIdx
c &= (1 << d) - 1
bits := min(8-bIdx, d-cIdx)
bIdx += bits
cIdx += bits
if bIdx == 8 {
b = b[1:]
bIdx = 0
}
}
f[i] = fieldElement(decompress(c, d))
}
if len(b) != 0 {
panic("mlkem: internal error: leftover bytes")
}
return f
}
// ringCompressAndEncode5 appends a 160-byte encoding of a ring element to s,
// compressing eight coefficients per five bytes.
//
// It implements Compress₅, according to FIPS 203, Definition 4.7,
// followed by ByteEncode₅, according to FIPS 203, Algorithm 5.
func ringCompressAndEncode5(s []byte, f ringElement) []byte {
return ringCompressAndEncode(s, f, 5)
}
// ringDecodeAndDecompress5 decodes a 160-byte encoding of a ring element where
// each five bits are mapped to an equidistant distribution.
//
// It implements ByteDecode₅, according to FIPS 203, Algorithm 6,
// followed by Decompress₅, according to FIPS 203, Definition 4.8.
func ringDecodeAndDecompress5(bb *[encodingSize5]byte) ringElement {
return ringDecodeAndDecompress(bb[:], 5)
}
// ringCompressAndEncode11 appends a 352-byte encoding of a ring element to s,
// compressing eight coefficients per eleven bytes.
//
// It implements Compress₁₁, according to FIPS 203, Definition 4.7,
// followed by ByteEncode₁₁, according to FIPS 203, Algorithm 5.
func ringCompressAndEncode11(s []byte, f ringElement) []byte {
return ringCompressAndEncode(s, f, 11)
}
// ringDecodeAndDecompress11 decodes a 352-byte encoding of a ring element where
// each eleven bits are mapped to an equidistant distribution.
//
// It implements ByteDecode₁₁, according to FIPS 203, Algorithm 6,
// followed by Decompress₁₁, according to FIPS 203, Definition 4.8.
func ringDecodeAndDecompress11(bb *[encodingSize11]byte) ringElement {
return ringDecodeAndDecompress(bb[:], 11)
}
// samplePolyCBD draws a ringElement from the special Dη distribution given a
// stream of random bytes generated by the PRF function, according to FIPS 203,
// Algorithm 8 and Definition 4.3.
func samplePolyCBD(s []byte, b byte) ringElement {
prf := sha3.NewShake256()
prf.Write(s)
prf.Write([]byte{b})
B := make([]byte, 64*2) // η = 2
prf.Read(B)
// SamplePolyCBD simply draws four (2η) bits for each coefficient, and adds
// the first two and subtracts the last two.
var f ringElement
for i := 0; i < n; i += 2 {
b := B[i/2]
b_7, b_6, b_5, b_4 := b>>7, b>>6&1, b>>5&1, b>>4&1
b_3, b_2, b_1, b_0 := b>>3&1, b>>2&1, b>>1&1, b&1
f[i] = fieldSub(fieldElement(b_0+b_1), fieldElement(b_2+b_3))
f[i+1] = fieldSub(fieldElement(b_4+b_5), fieldElement(b_6+b_7))
}
return f
}
// nttElement is an NTT representation, an element of T_q, represented as an
// array according to FIPS 203, Section 2.4.4.
type nttElement [n]fieldElement
// gammas are the values ζ^2BitRev7(i)+1 mod q for each index i, according to
// FIPS 203, Appendix A (with negative values reduced to positive).
var gammas = [128]fieldElement{17, 3312, 2761, 568, 583, 2746, 2649, 680, 1637, 1692, 723, 2606, 2288, 1041, 1100, 2229, 1409, 1920, 2662, 667, 3281, 48, 233, 3096, 756, 2573, 2156, 1173, 3015, 314, 3050, 279, 1703, 1626, 1651, 1678, 2789, 540, 1789, 1540, 1847, 1482, 952, 2377, 1461, 1868, 2687, 642, 939, 2390, 2308, 1021, 2437, 892, 2388, 941, 733, 2596, 2337, 992, 268, 3061, 641, 2688, 1584, 1745, 2298, 1031, 2037, 1292, 3220, 109, 375, 2954, 2549, 780, 2090, 1239, 1645, 1684, 1063, 2266, 319, 3010, 2773, 556, 757, 2572, 2099, 1230, 561, 2768, 2466, 863, 2594, 735, 2804, 525, 1092, 2237, 403, 2926, 1026, 2303, 1143, 2186, 2150, 1179, 2775, 554, 886, 2443, 1722, 1607, 1212, 2117, 1874, 1455, 1029, 2300, 2110, 1219, 2935, 394, 885, 2444, 2154, 1175}
// nttMul multiplies two nttElements.
//
// It implements MultiplyNTTs, according to FIPS 203, Algorithm 11.
func nttMul(f, g nttElement) nttElement {
var h nttElement
// We use i += 2 for bounds check elimination. See https://go.dev/issue/66826.
for i := 0; i < 256; i += 2 {
a0, a1 := f[i], f[i+1]
b0, b1 := g[i], g[i+1]
h[i] = fieldAddMul(a0, b0, fieldMul(a1, b1), gammas[i/2])
h[i+1] = fieldAddMul(a0, b1, a1, b0)
}
return h
}
// zetas are the values ζ^BitRev7(k) mod q for each index k, according to FIPS
// 203, Appendix A.
var zetas = [128]fieldElement{1, 1729, 2580, 3289, 2642, 630, 1897, 848, 1062, 1919, 193, 797, 2786, 3260, 569, 1746, 296, 2447, 1339, 1476, 3046, 56, 2240, 1333, 1426, 2094, 535, 2882, 2393, 2879, 1974, 821, 289, 331, 3253, 1756, 1197, 2304, 2277, 2055, 650, 1977, 2513, 632, 2865, 33, 1320, 1915, 2319, 1435, 807, 452, 1438, 2868, 1534, 2402, 2647, 2617, 1481, 648, 2474, 3110, 1227, 910, 17, 2761, 583, 2649, 1637, 723, 2288, 1100, 1409, 2662, 3281, 233, 756, 2156, 3015, 3050, 1703, 1651, 2789, 1789, 1847, 952, 1461, 2687, 939, 2308, 2437, 2388, 733, 2337, 268, 641, 1584, 2298, 2037, 3220, 375, 2549, 2090, 1645, 1063, 319, 2773, 757, 2099, 561, 2466, 2594, 2804, 1092, 403, 1026, 1143, 2150, 2775, 886, 1722, 1212, 1874, 1029, 2110, 2935, 885, 2154}
// ntt maps a ringElement to its nttElement representation.
//
// It implements NTT, according to FIPS 203, Algorithm 9.
func ntt(f ringElement) nttElement {
k := 1
for len := 128; len >= 2; len /= 2 {
for start := 0; start < 256; start += 2 * len {
zeta := zetas[k]
k++
// Bounds check elimination hint.
f, flen := f[start:start+len], f[start+len:start+len+len]
for j := 0; j < len; j++ {
t := fieldMul(zeta, flen[j])
flen[j] = fieldSub(f[j], t)
f[j] = fieldAdd(f[j], t)
}
}
}
return nttElement(f)
}
// inverseNTT maps a nttElement back to the ringElement it represents.
//
// It implements NTT⁻¹, according to FIPS 203, Algorithm 10.
func inverseNTT(f nttElement) ringElement {
k := 127
for len := 2; len <= 128; len *= 2 {
for start := 0; start < 256; start += 2 * len {
zeta := zetas[k]
k--
// Bounds check elimination hint.
f, flen := f[start:start+len], f[start+len:start+len+len]
for j := 0; j < len; j++ {
t := f[j]
f[j] = fieldAdd(t, flen[j])
flen[j] = fieldMulSub(zeta, flen[j], t)
}
}
}
for i := range f {
f[i] = fieldMul(f[i], 3303) // 3303 = 128⁻¹ mod q
}
return ringElement(f)
}
// sampleNTT draws a uniformly random nttElement from a stream of uniformly
// random bytes generated by the XOF function, according to FIPS 203,
// Algorithm 7.
func sampleNTT(rho []byte, ii, jj byte) nttElement {
B := sha3.NewShake128()
B.Write(rho)
B.Write([]byte{ii, jj})
// SampleNTT essentially draws 12 bits at a time from r, interprets them in
// little-endian, and rejects values higher than q, until it drew 256
// values. (The rejection rate is approximately 19%.)
//
// To do this from a bytes stream, it draws three bytes at a time, and
// splits them into two uint16 appropriately masked.
//
// r₀ r₁ r₂
// |- - - - - - - -|- - - - - - - -|- - - - - - - -|
//
// Uint16(r₀ || r₁)
// |- - - - - - - - - - - - - - - -|
// |- - - - - - - - - - - -|
// d₁
//
// Uint16(r₁ || r₂)
// |- - - - - - - - - - - - - - - -|
// |- - - - - - - - - - - -|
// d₂
//
// Note that in little-endian, the rightmost bits are the most significant
// bits (dropped with a mask) and the leftmost bits are the least
// significant bits (dropped with a right shift).
var a nttElement
var j int // index into a
var buf [24]byte // buffered reads from B
off := len(buf) // index into buf, starts in a "buffer fully consumed" state
for {
if off >= len(buf) {
B.Read(buf[:])
off = 0
}
d1 := byteorder.LEUint16(buf[off:]) & 0b1111_1111_1111
d2 := byteorder.LEUint16(buf[off+1:]) >> 4
off += 3
if d1 < q {
a[j] = fieldElement(d1)
j++
}
if j >= len(a) {
break
}
if d2 < q {
a[j] = fieldElement(d2)
j++
}
if j >= len(a) {
break
}
}
return a
}

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// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package mlkem implements the quantum-resistant key encapsulation method
// ML-KEM (formerly known as Kyber), as specified in [NIST FIPS 203].
//
// [NIST FIPS 203]: https://doi.org/10.6028/NIST.FIPS.203
package mlkem
// This package targets security, correctness, simplicity, readability, and
// reviewability as its primary goals. All critical operations are performed in
// constant time.
//
// Variable and function names, as well as code layout, are selected to
// facilitate reviewing the implementation against the NIST FIPS 203 document.
//
// Reviewers unfamiliar with polynomials or linear algebra might find the
// background at https://words.filippo.io/kyber-math/ useful.
//
// This file implements the recommended parameter set ML-KEM-768. The ML-KEM-1024
// parameter set implementation is auto-generated from this file.
//
//go:generate go run generate1024.go -input mlkem768.go -output mlkem1024.go
import (
"bytes"
//"github.com/xtls/reality/fips140"
"github.com/xtls/reality/drbg"
"github.com/xtls/reality/sha3"
"github.com/xtls/reality/subtle"
"errors"
)
const (
// ML-KEM global constants.
n = 256
q = 3329
// encodingSizeX is the byte size of a ringElement or nttElement encoded
// by ByteEncode_X (FIPS 203, Algorithm 5).
encodingSize12 = n * 12 / 8
encodingSize11 = n * 11 / 8
encodingSize10 = n * 10 / 8
encodingSize5 = n * 5 / 8
encodingSize4 = n * 4 / 8
encodingSize1 = n * 1 / 8
messageSize = encodingSize1
SharedKeySize = 32
SeedSize = 32 + 32
)
// ML-KEM-768 parameters.
const (
k = 3
CiphertextSize768 = k*encodingSize10 + encodingSize4
EncapsulationKeySize768 = k*encodingSize12 + 32
decapsulationKeySize768 = k*encodingSize12 + EncapsulationKeySize768 + 32 + 32
)
// ML-KEM-1024 parameters.
const (
k1024 = 4
CiphertextSize1024 = k1024*encodingSize11 + encodingSize5
EncapsulationKeySize1024 = k1024*encodingSize12 + 32
decapsulationKeySize1024 = k1024*encodingSize12 + EncapsulationKeySize1024 + 32 + 32
)
// A DecapsulationKey768 is the secret key used to decapsulate a shared key from a
// ciphertext. It includes various precomputed values.
type DecapsulationKey768 struct {
d [32]byte // decapsulation key seed
z [32]byte // implicit rejection sampling seed
ρ [32]byte // sampleNTT seed for A, stored for the encapsulation key
h [32]byte // H(ek), stored for ML-KEM.Decaps_internal
encryptionKey
decryptionKey
}
// Bytes returns the decapsulation key as a 64-byte seed in the "d || z" form.
//
// The decapsulation key must be kept secret.
func (dk *DecapsulationKey768) Bytes() []byte {
var b [SeedSize]byte
copy(b[:], dk.d[:])
copy(b[32:], dk.z[:])
return b[:]
}
// TestingOnlyExpandedBytes768 returns the decapsulation key as a byte slice
// using the full expanded NIST encoding.
//
// This should only be used for ACVP testing. For all other purposes prefer
// the Bytes method that returns the (much smaller) seed.
func TestingOnlyExpandedBytes768(dk *DecapsulationKey768) []byte {
b := make([]byte, 0, decapsulationKeySize768)
// ByteEncode₁₂(s)
for i := range dk.s {
b = polyByteEncode(b, dk.s[i])
}
// ByteEncode₁₂(t) || ρ
for i := range dk.t {
b = polyByteEncode(b, dk.t[i])
}
b = append(b, dk.ρ[:]...)
// H(ek) || z
b = append(b, dk.h[:]...)
b = append(b, dk.z[:]...)
return b
}
// EncapsulationKey returns the public encapsulation key necessary to produce
// ciphertexts.
func (dk *DecapsulationKey768) EncapsulationKey() *EncapsulationKey768 {
return &EncapsulationKey768{
ρ: dk.ρ,
h: dk.h,
encryptionKey: dk.encryptionKey,
}
}
// An EncapsulationKey768 is the public key used to produce ciphertexts to be
// decapsulated by the corresponding [DecapsulationKey768].
type EncapsulationKey768 struct {
ρ [32]byte // sampleNTT seed for A
h [32]byte // H(ek)
encryptionKey
}
// Bytes returns the encapsulation key as a byte slice.
func (ek *EncapsulationKey768) Bytes() []byte {
// The actual logic is in a separate function to outline this allocation.
b := make([]byte, 0, EncapsulationKeySize768)
return ek.bytes(b)
}
func (ek *EncapsulationKey768) bytes(b []byte) []byte {
for i := range ek.t {
b = polyByteEncode(b, ek.t[i])
}
b = append(b, ek.ρ[:]...)
return b
}
// encryptionKey is the parsed and expanded form of a PKE encryption key.
type encryptionKey struct {
t [k]nttElement // ByteDecode₁₂(ek[:384k])
a [k * k]nttElement // A[i*k+j] = sampleNTT(ρ, j, i)
}
// decryptionKey is the parsed and expanded form of a PKE decryption key.
type decryptionKey struct {
s [k]nttElement // ByteDecode₁₂(dk[:decryptionKeySize])
}
// GenerateKey768 generates a new decapsulation key, drawing random bytes from
// a DRBG. The decapsulation key must be kept secret.
func GenerateKey768() (*DecapsulationKey768, error) {
// The actual logic is in a separate function to outline this allocation.
dk := &DecapsulationKey768{}
return generateKey(dk)
}
func generateKey(dk *DecapsulationKey768) (*DecapsulationKey768, error) {
var d [32]byte
drbg.Read(d[:])
var z [32]byte
drbg.Read(z[:])
kemKeyGen(dk, &d, &z)
// if err := fips140.PCT("ML-KEM PCT", func() error { return kemPCT(dk) }); err != nil {
// // This clearly can't happen, but FIPS 140-3 requires us to check.
// panic(err)
// }
//fips140.RecordApproved()
return dk, nil
}
// GenerateKeyInternal768 is a derandomized version of GenerateKey768,
// exclusively for use in tests.
func GenerateKeyInternal768(d, z *[32]byte) *DecapsulationKey768 {
dk := &DecapsulationKey768{}
kemKeyGen(dk, d, z)
return dk
}
// NewDecapsulationKey768 parses a decapsulation key from a 64-byte
// seed in the "d || z" form. The seed must be uniformly random.
func NewDecapsulationKey768(seed []byte) (*DecapsulationKey768, error) {
// The actual logic is in a separate function to outline this allocation.
dk := &DecapsulationKey768{}
return newKeyFromSeed(dk, seed)
}
func newKeyFromSeed(dk *DecapsulationKey768, seed []byte) (*DecapsulationKey768, error) {
if len(seed) != SeedSize {
return nil, errors.New("mlkem: invalid seed length")
}
d := (*[32]byte)(seed[:32])
z := (*[32]byte)(seed[32:])
kemKeyGen(dk, d, z)
// if err := fips140.PCT("ML-KEM PCT", func() error { return kemPCT(dk) }); err != nil {
// // This clearly can't happen, but FIPS 140-3 requires us to check.
// panic(err)
// }
//fips140.RecordApproved()
return dk, nil
}
// TestingOnlyNewDecapsulationKey768 parses a decapsulation key from its expanded NIST format.
//
// Bytes() must not be called on the returned key, as it will not produce the
// original seed.
//
// This function should only be used for ACVP testing. Prefer NewDecapsulationKey768 for all
// other purposes.
func TestingOnlyNewDecapsulationKey768(b []byte) (*DecapsulationKey768, error) {
if len(b) != decapsulationKeySize768 {
return nil, errors.New("mlkem: invalid NIST decapsulation key length")
}
dk := &DecapsulationKey768{}
for i := range dk.s {
var err error
dk.s[i], err = polyByteDecode[nttElement](b[:encodingSize12])
if err != nil {
return nil, errors.New("mlkem: invalid secret key encoding")
}
b = b[encodingSize12:]
}
ek, err := NewEncapsulationKey768(b[:EncapsulationKeySize768])
if err != nil {
return nil, err
}
dk.ρ = ek.ρ
dk.h = ek.h
dk.encryptionKey = ek.encryptionKey
b = b[EncapsulationKeySize768:]
if !bytes.Equal(dk.h[:], b[:32]) {
return nil, errors.New("mlkem: inconsistent H(ek) in encoded bytes")
}
b = b[32:]
copy(dk.z[:], b)
// Generate a random d value for use in Bytes(). This is a safety mechanism
// that avoids returning a broken key vs a random key if this function is
// called in contravention of the TestingOnlyNewDecapsulationKey768 function
// comment advising against it.
drbg.Read(dk.d[:])
return dk, nil
}
// kemKeyGen generates a decapsulation key.
//
// It implements ML-KEM.KeyGen_internal according to FIPS 203, Algorithm 16, and
// K-PKE.KeyGen according to FIPS 203, Algorithm 13. The two are merged to save
// copies and allocations.
func kemKeyGen(dk *DecapsulationKey768, d, z *[32]byte) {
dk.d = *d
dk.z = *z
g := sha3.New512()
g.Write(d[:])
g.Write([]byte{k}) // Module dimension as a domain separator.
G := g.Sum(make([]byte, 0, 64))
ρ, σ := G[:32], G[32:]
dk.ρ = [32]byte(ρ)
A := &dk.a
for i := byte(0); i < k; i++ {
for j := byte(0); j < k; j++ {
A[i*k+j] = sampleNTT(ρ, j, i)
}
}
var N byte
s := &dk.s
for i := range s {
s[i] = ntt(samplePolyCBD(σ, N))
N++
}
e := make([]nttElement, k)
for i := range e {
e[i] = ntt(samplePolyCBD(σ, N))
N++
}
t := &dk.t
for i := range t { // t = A ◦ s + e
t[i] = e[i]
for j := range s {
t[i] = polyAdd(t[i], nttMul(A[i*k+j], s[j]))
}
}
H := sha3.New256()
ek := dk.EncapsulationKey().Bytes()
H.Write(ek)
H.Sum(dk.h[:0])
}
// kemPCT performs a Pairwise Consistency Test per FIPS 140-3 IG 10.3.A
// Additional Comment 1: "For key pairs generated for use with approved KEMs in
// FIPS 203, the PCT shall consist of applying the encapsulation key ek to
// encapsulate a shared secret K leading to ciphertext c, and then applying
// decapsulation key dk to retrieve the same shared secret K. The PCT passes if
// the two shared secret K values are equal. The PCT shall be performed either
// when keys are generated/imported, prior to the first exportation, or prior to
// the first operational use (if not exported before the first use)."
func kemPCT(dk *DecapsulationKey768) error {
ek := dk.EncapsulationKey()
K, c := ek.Encapsulate()
K1, err := dk.Decapsulate(c)
if err != nil {
return err
}
if subtle.ConstantTimeCompare(K, K1) != 1 {
return errors.New("mlkem: PCT failed")
}
return nil
}
// Encapsulate generates a shared key and an associated ciphertext from an
// encapsulation key, drawing random bytes from a DRBG.
//
// The shared key must be kept secret.
func (ek *EncapsulationKey768) Encapsulate() (sharedKey, ciphertext []byte) {
// The actual logic is in a separate function to outline this allocation.
var cc [CiphertextSize768]byte
return ek.encapsulate(&cc)
}
func (ek *EncapsulationKey768) encapsulate(cc *[CiphertextSize768]byte) (sharedKey, ciphertext []byte) {
var m [messageSize]byte
drbg.Read(m[:])
// Note that the modulus check (step 2 of the encapsulation key check from
// FIPS 203, Section 7.2) is performed by polyByteDecode in parseEK.
//fips140.RecordApproved()
return kemEncaps(cc, ek, &m)
}
// EncapsulateInternal is a derandomized version of Encapsulate, exclusively for
// use in tests.
func (ek *EncapsulationKey768) EncapsulateInternal(m *[32]byte) (sharedKey, ciphertext []byte) {
cc := &[CiphertextSize768]byte{}
return kemEncaps(cc, ek, m)
}
// kemEncaps generates a shared key and an associated ciphertext.
//
// It implements ML-KEM.Encaps_internal according to FIPS 203, Algorithm 17.
func kemEncaps(cc *[CiphertextSize768]byte, ek *EncapsulationKey768, m *[messageSize]byte) (K, c []byte) {
g := sha3.New512()
g.Write(m[:])
g.Write(ek.h[:])
G := g.Sum(nil)
K, r := G[:SharedKeySize], G[SharedKeySize:]
c = pkeEncrypt(cc, &ek.encryptionKey, m, r)
return K, c
}
// NewEncapsulationKey768 parses an encapsulation key from its encoded form.
// If the encapsulation key is not valid, NewEncapsulationKey768 returns an error.
func NewEncapsulationKey768(encapsulationKey []byte) (*EncapsulationKey768, error) {
// The actual logic is in a separate function to outline this allocation.
ek := &EncapsulationKey768{}
return parseEK(ek, encapsulationKey)
}
// parseEK parses an encryption key from its encoded form.
//
// It implements the initial stages of K-PKE.Encrypt according to FIPS 203,
// Algorithm 14.
func parseEK(ek *EncapsulationKey768, ekPKE []byte) (*EncapsulationKey768, error) {
if len(ekPKE) != EncapsulationKeySize768 {
return nil, errors.New("mlkem: invalid encapsulation key length")
}
h := sha3.New256()
h.Write(ekPKE)
h.Sum(ek.h[:0])
for i := range ek.t {
var err error
ek.t[i], err = polyByteDecode[nttElement](ekPKE[:encodingSize12])
if err != nil {
return nil, err
}
ekPKE = ekPKE[encodingSize12:]
}
copy(ek.ρ[:], ekPKE)
for i := byte(0); i < k; i++ {
for j := byte(0); j < k; j++ {
ek.a[i*k+j] = sampleNTT(ek.ρ[:], j, i)
}
}
return ek, nil
}
// pkeEncrypt encrypt a plaintext message.
//
// It implements K-PKE.Encrypt according to FIPS 203, Algorithm 14, although the
// computation of t and AT is done in parseEK.
func pkeEncrypt(cc *[CiphertextSize768]byte, ex *encryptionKey, m *[messageSize]byte, rnd []byte) []byte {
var N byte
r, e1 := make([]nttElement, k), make([]ringElement, k)
for i := range r {
r[i] = ntt(samplePolyCBD(rnd, N))
N++
}
for i := range e1 {
e1[i] = samplePolyCBD(rnd, N)
N++
}
e2 := samplePolyCBD(rnd, N)
u := make([]ringElement, k) // NTT⁻¹(AT ◦ r) + e1
for i := range u {
u[i] = e1[i]
for j := range r {
// Note that i and j are inverted, as we need the transposed of A.
u[i] = polyAdd(u[i], inverseNTT(nttMul(ex.a[j*k+i], r[j])))
}
}
μ := ringDecodeAndDecompress1(m)
var vNTT nttElement // t⊺ ◦ r
for i := range ex.t {
vNTT = polyAdd(vNTT, nttMul(ex.t[i], r[i]))
}
v := polyAdd(polyAdd(inverseNTT(vNTT), e2), μ)
c := cc[:0]
for _, f := range u {
c = ringCompressAndEncode10(c, f)
}
c = ringCompressAndEncode4(c, v)
return c
}
// Decapsulate generates a shared key from a ciphertext and a decapsulation key.
// If the ciphertext is not valid, Decapsulate returns an error.
//
// The shared key must be kept secret.
func (dk *DecapsulationKey768) Decapsulate(ciphertext []byte) (sharedKey []byte, err error) {
if len(ciphertext) != CiphertextSize768 {
return nil, errors.New("mlkem: invalid ciphertext length")
}
c := (*[CiphertextSize768]byte)(ciphertext)
// Note that the hash check (step 3 of the decapsulation input check from
// FIPS 203, Section 7.3) is foregone as a DecapsulationKey is always
// validly generated by ML-KEM.KeyGen_internal.
return kemDecaps(dk, c), nil
}
// kemDecaps produces a shared key from a ciphertext.
//
// It implements ML-KEM.Decaps_internal according to FIPS 203, Algorithm 18.
func kemDecaps(dk *DecapsulationKey768, c *[CiphertextSize768]byte) (K []byte) {
//fips140.RecordApproved()
m := pkeDecrypt(&dk.decryptionKey, c)
g := sha3.New512()
g.Write(m[:])
g.Write(dk.h[:])
G := g.Sum(make([]byte, 0, 64))
Kprime, r := G[:SharedKeySize], G[SharedKeySize:]
J := sha3.NewShake256()
J.Write(dk.z[:])
J.Write(c[:])
Kout := make([]byte, SharedKeySize)
J.Read(Kout)
var cc [CiphertextSize768]byte
c1 := pkeEncrypt(&cc, &dk.encryptionKey, (*[32]byte)(m), r)
subtle.ConstantTimeCopy(subtle.ConstantTimeCompare(c[:], c1), Kout, Kprime)
return Kout
}
// pkeDecrypt decrypts a ciphertext.
//
// It implements K-PKE.Decrypt according to FIPS 203, Algorithm 15,
// although s is retained from kemKeyGen.
func pkeDecrypt(dx *decryptionKey, c *[CiphertextSize768]byte) []byte {
u := make([]ringElement, k)
for i := range u {
b := (*[encodingSize10]byte)(c[encodingSize10*i : encodingSize10*(i+1)])
u[i] = ringDecodeAndDecompress10(b)
}
b := (*[encodingSize4]byte)(c[encodingSize10*k:])
v := ringDecodeAndDecompress4(b)
var mask nttElement // s⊺ ◦ NTT(u)
for i := range dx.s {
mask = polyAdd(mask, nttMul(dx.s[i], ntt(u[i])))
}
w := polySub(v, inverseNTT(mask))
return ringCompressAndEncode1(nil, w)
}

886
mlkem768/mlkem768.go
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@ -1,886 +0,0 @@
// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package mlkem768 implements the quantum-resistant key encapsulation method
// ML-KEM (formerly known as Kyber).
//
// Only the recommended ML-KEM-768 parameter set is provided.
//
// The version currently implemented is the one specified by [NIST FIPS 203 ipd],
// with the unintentional transposition of the matrix A reverted to match the
// behavior of [Kyber version 3.0]. Future versions of this package might
// introduce backwards incompatible changes to implement changes to FIPS 203.
//
// [Kyber version 3.0]: https://pq-crystals.org/kyber/data/kyber-specification-round3-20210804.pdf
// [NIST FIPS 203 ipd]: https://doi.org/10.6028/NIST.FIPS.203.ipd
package mlkem768
// This package targets security, correctness, simplicity, readability, and
// reviewability as its primary goals. All critical operations are performed in
// constant time.
//
// Variable and function names, as well as code layout, are selected to
// facilitate reviewing the implementation against the NIST FIPS 203 ipd
// document.
//
// Reviewers unfamiliar with polynomials or linear algebra might find the
// background at https://words.filippo.io/kyber-math/ useful.
import (
"crypto/rand"
"crypto/subtle"
"encoding/binary"
"errors"
"golang.org/x/crypto/sha3"
)
const (
// ML-KEM global constants.
n = 256
q = 3329
log2q = 12
// ML-KEM-768 parameters. The code makes assumptions based on these values,
// they can't be changed blindly.
k = 3
η = 2
du = 10
dv = 4
// encodingSizeX is the byte size of a ringElement or nttElement encoded
// by ByteEncode_X (FIPS 203 (DRAFT), Algorithm 4).
encodingSize12 = n * log2q / 8
encodingSize10 = n * du / 8
encodingSize4 = n * dv / 8
encodingSize1 = n * 1 / 8
messageSize = encodingSize1
decryptionKeySize = k * encodingSize12
encryptionKeySize = k*encodingSize12 + 32
CiphertextSize = k*encodingSize10 + encodingSize4
EncapsulationKeySize = encryptionKeySize
DecapsulationKeySize = decryptionKeySize + encryptionKeySize + 32 + 32
SharedKeySize = 32
SeedSize = 32 + 32
)
// A DecapsulationKey is the secret key used to decapsulate a shared key from a
// ciphertext. It includes various precomputed values.
type DecapsulationKey struct {
dk [DecapsulationKeySize]byte
encryptionKey
decryptionKey
}
// Bytes returns the extended encoding of the decapsulation key, according to
// FIPS 203 (DRAFT).
func (dk *DecapsulationKey) Bytes() []byte {
var b [DecapsulationKeySize]byte
copy(b[:], dk.dk[:])
return b[:]
}
// EncapsulationKey returns the public encapsulation key necessary to produce
// ciphertexts.
func (dk *DecapsulationKey) EncapsulationKey() []byte {
var b [EncapsulationKeySize]byte
copy(b[:], dk.dk[decryptionKeySize:])
return b[:]
}
// encryptionKey is the parsed and expanded form of a PKE encryption key.
type encryptionKey struct {
t [k]nttElement // ByteDecode₁₂(ek[:384k])
A [k * k]nttElement // A[i*k+j] = sampleNTT(ρ, j, i)
}
// decryptionKey is the parsed and expanded form of a PKE decryption key.
type decryptionKey struct {
s [k]nttElement // ByteDecode₁₂(dk[:decryptionKeySize])
}
// GenerateKey generates a new decapsulation key, drawing random bytes from
// crypto/rand. The decapsulation key must be kept secret.
func GenerateKey() (*DecapsulationKey, error) {
// The actual logic is in a separate function to outline this allocation.
dk := &DecapsulationKey{}
return generateKey(dk)
}
func generateKey(dk *DecapsulationKey) (*DecapsulationKey, error) {
var d [32]byte
if _, err := rand.Read(d[:]); err != nil {
return nil, errors.New("mlkem768: crypto/rand Read failed: " + err.Error())
}
var z [32]byte
if _, err := rand.Read(z[:]); err != nil {
return nil, errors.New("mlkem768: crypto/rand Read failed: " + err.Error())
}
return kemKeyGen(dk, &d, &z), nil
}
// NewKeyFromSeed deterministically generates a decapsulation key from a 64-byte
// seed in the "d || z" form. The seed must be uniformly random.
func NewKeyFromSeed(seed []byte) (*DecapsulationKey, error) {
// The actual logic is in a separate function to outline this allocation.
dk := &DecapsulationKey{}
return newKeyFromSeed(dk, seed)
}
func newKeyFromSeed(dk *DecapsulationKey, seed []byte) (*DecapsulationKey, error) {
if len(seed) != SeedSize {
return nil, errors.New("mlkem768: invalid seed length")
}
d := (*[32]byte)(seed[:32])
z := (*[32]byte)(seed[32:])
return kemKeyGen(dk, d, z), nil
}
// NewKeyFromExtendedEncoding parses a decapsulation key from its FIPS 203
// (DRAFT) extended encoding.
func NewKeyFromExtendedEncoding(decapsulationKey []byte) (*DecapsulationKey, error) {
// The actual logic is in a separate function to outline this allocation.
dk := &DecapsulationKey{}
return newKeyFromExtendedEncoding(dk, decapsulationKey)
}
func newKeyFromExtendedEncoding(dk *DecapsulationKey, dkBytes []byte) (*DecapsulationKey, error) {
if len(dkBytes) != DecapsulationKeySize {
return nil, errors.New("mlkem768: invalid decapsulation key length")
}
// Note that we don't check that H(ek) matches ekPKE, as that's not
// specified in FIPS 203 (DRAFT). This is one reason to prefer the seed
// private key format.
dk.dk = [DecapsulationKeySize]byte(dkBytes)
dkPKE := dkBytes[:decryptionKeySize]
if err := parseDK(&dk.decryptionKey, dkPKE); err != nil {
return nil, err
}
ekPKE := dkBytes[decryptionKeySize : decryptionKeySize+encryptionKeySize]
if err := parseEK(&dk.encryptionKey, ekPKE); err != nil {
return nil, err
}
return dk, nil
}
// kemKeyGen generates a decapsulation key.
//
// It implements ML-KEM.KeyGen according to FIPS 203 (DRAFT), Algorithm 15, and
// K-PKE.KeyGen according to FIPS 203 (DRAFT), Algorithm 12. The two are merged
// to save copies and allocations.
func kemKeyGen(dk *DecapsulationKey, d, z *[32]byte) *DecapsulationKey {
if dk == nil {
dk = &DecapsulationKey{}
}
G := sha3.Sum512(d[:])
ρ, σ := G[:32], G[32:]
A := &dk.A
for i := byte(0); i < k; i++ {
for j := byte(0); j < k; j++ {
// Note that this is consistent with Kyber round 3, rather than with
// the initial draft of FIPS 203, because NIST signaled that the
// change was involuntary and will be reverted.
A[i*k+j] = sampleNTT(ρ, j, i)
}
}
var N byte
s := &dk.s
for i := range s {
s[i] = ntt(samplePolyCBD(σ, N))
N++
}
e := make([]nttElement, k)
for i := range e {
e[i] = ntt(samplePolyCBD(σ, N))
N++
}
t := &dk.t
for i := range t { // t = A ◦ s + e
t[i] = e[i]
for j := range s {
t[i] = polyAdd(t[i], nttMul(A[i*k+j], s[j]))
}
}
// dkPKE ← ByteEncode₁₂(s)
// ekPKE ← ByteEncode₁₂(t) || ρ
// ek ← ekPKE
// dk ← dkPKE || ek || H(ek) || z
dkB := dk.dk[:0]
for i := range s {
dkB = polyByteEncode(dkB, s[i])
}
for i := range t {
dkB = polyByteEncode(dkB, t[i])
}
dkB = append(dkB, ρ...)
H := sha3.New256()
H.Write(dkB[decryptionKeySize:])
dkB = H.Sum(dkB)
dkB = append(dkB, z[:]...)
if len(dkB) != len(dk.dk) {
panic("mlkem768: internal error: invalid decapsulation key size")
}
return dk
}
// Encapsulate generates a shared key and an associated ciphertext from an
// encapsulation key, drawing random bytes from crypto/rand.
// If the encapsulation key is not valid, Encapsulate returns an error.
//
// The shared key must be kept secret.
func Encapsulate(encapsulationKey []byte) (ciphertext, sharedKey []byte, err error) {
// The actual logic is in a separate function to outline this allocation.
var cc [CiphertextSize]byte
return encapsulate(&cc, encapsulationKey)
}
func encapsulate(cc *[CiphertextSize]byte, encapsulationKey []byte) (ciphertext, sharedKey []byte, err error) {
if len(encapsulationKey) != EncapsulationKeySize {
return nil, nil, errors.New("mlkem768: invalid encapsulation key length")
}
var m [messageSize]byte
if _, err := rand.Read(m[:]); err != nil {
return nil, nil, errors.New("mlkem768: crypto/rand Read failed: " + err.Error())
}
return kemEncaps(cc, encapsulationKey, &m)
}
// kemEncaps generates a shared key and an associated ciphertext.
//
// It implements ML-KEM.Encaps according to FIPS 203 (DRAFT), Algorithm 16.
func kemEncaps(cc *[CiphertextSize]byte, ek []byte, m *[messageSize]byte) (c, K []byte, err error) {
if cc == nil {
cc = &[CiphertextSize]byte{}
}
H := sha3.Sum256(ek[:])
g := sha3.New512()
g.Write(m[:])
g.Write(H[:])
G := g.Sum(nil)
K, r := G[:SharedKeySize], G[SharedKeySize:]
var ex encryptionKey
if err := parseEK(&ex, ek[:]); err != nil {
return nil, nil, err
}
c = pkeEncrypt(cc, &ex, m, r)
return c, K, nil
}
// parseEK parses an encryption key from its encoded form.
//
// It implements the initial stages of K-PKE.Encrypt according to FIPS 203
// (DRAFT), Algorithm 13.
func parseEK(ex *encryptionKey, ekPKE []byte) error {
if len(ekPKE) != encryptionKeySize {
return errors.New("mlkem768: invalid encryption key length")
}
for i := range ex.t {
var err error
ex.t[i], err = polyByteDecode[nttElement](ekPKE[:encodingSize12])
if err != nil {
return err
}
ekPKE = ekPKE[encodingSize12:]
}
ρ := ekPKE
for i := byte(0); i < k; i++ {
for j := byte(0); j < k; j++ {
// See the note in pkeKeyGen about the order of the indices being
// consistent with Kyber round 3.
ex.A[i*k+j] = sampleNTT(ρ, j, i)
}
}
return nil
}
// pkeEncrypt encrypt a plaintext message.
//
// It implements K-PKE.Encrypt according to FIPS 203 (DRAFT), Algorithm 13,
// although the computation of t and AT is done in parseEK.
func pkeEncrypt(cc *[CiphertextSize]byte, ex *encryptionKey, m *[messageSize]byte, rnd []byte) []byte {
var N byte
r, e1 := make([]nttElement, k), make([]ringElement, k)
for i := range r {
r[i] = ntt(samplePolyCBD(rnd, N))
N++
}
for i := range e1 {
e1[i] = samplePolyCBD(rnd, N)
N++
}
e2 := samplePolyCBD(rnd, N)
u := make([]ringElement, k) // NTT⁻¹(AT ◦ r) + e1
for i := range u {
u[i] = e1[i]
for j := range r {
// Note that i and j are inverted, as we need the transposed of A.
u[i] = polyAdd(u[i], inverseNTT(nttMul(ex.A[j*k+i], r[j])))
}
}
μ := ringDecodeAndDecompress1(m)
var vNTT nttElement // t⊺ ◦ r
for i := range ex.t {
vNTT = polyAdd(vNTT, nttMul(ex.t[i], r[i]))
}
v := polyAdd(polyAdd(inverseNTT(vNTT), e2), μ)
c := cc[:0]
for _, f := range u {
c = ringCompressAndEncode10(c, f)
}
c = ringCompressAndEncode4(c, v)
return c
}
// Decapsulate generates a shared key from a ciphertext and a decapsulation key.
// If the ciphertext is not valid, Decapsulate returns an error.
//
// The shared key must be kept secret.
func Decapsulate(dk *DecapsulationKey, ciphertext []byte) (sharedKey []byte, err error) {
if len(ciphertext) != CiphertextSize {
return nil, errors.New("mlkem768: invalid ciphertext length")
}
c := (*[CiphertextSize]byte)(ciphertext)
return kemDecaps(dk, c), nil
}
// kemDecaps produces a shared key from a ciphertext.
//
// It implements ML-KEM.Decaps according to FIPS 203 (DRAFT), Algorithm 17.
func kemDecaps(dk *DecapsulationKey, c *[CiphertextSize]byte) (K []byte) {
h := dk.dk[decryptionKeySize+encryptionKeySize : decryptionKeySize+encryptionKeySize+32]
z := dk.dk[decryptionKeySize+encryptionKeySize+32:]
m := pkeDecrypt(&dk.decryptionKey, c)
g := sha3.New512()
g.Write(m[:])
g.Write(h)
G := g.Sum(nil)
Kprime, r := G[:SharedKeySize], G[SharedKeySize:]
J := sha3.NewShake256()
J.Write(z)
J.Write(c[:])
Kout := make([]byte, SharedKeySize)
J.Read(Kout)
var cc [CiphertextSize]byte
c1 := pkeEncrypt(&cc, &dk.encryptionKey, (*[32]byte)(m), r)
subtle.ConstantTimeCopy(subtle.ConstantTimeCompare(c[:], c1), Kout, Kprime)
return Kout
}
// parseDK parses a decryption key from its encoded form.
//
// It implements the computation of s from K-PKE.Decrypt according to FIPS 203
// (DRAFT), Algorithm 14.
func parseDK(dx *decryptionKey, dkPKE []byte) error {
if len(dkPKE) != decryptionKeySize {
return errors.New("mlkem768: invalid decryption key length")
}
for i := range dx.s {
f, err := polyByteDecode[nttElement](dkPKE[:encodingSize12])
if err != nil {
return err
}
dx.s[i] = f
dkPKE = dkPKE[encodingSize12:]
}
return nil
}
// pkeDecrypt decrypts a ciphertext.
//
// It implements K-PKE.Decrypt according to FIPS 203 (DRAFT), Algorithm 14,
// although the computation of s is done in parseDK.
func pkeDecrypt(dx *decryptionKey, c *[CiphertextSize]byte) []byte {
u := make([]ringElement, k)
for i := range u {
b := (*[encodingSize10]byte)(c[encodingSize10*i : encodingSize10*(i+1)])
u[i] = ringDecodeAndDecompress10(b)
}
b := (*[encodingSize4]byte)(c[encodingSize10*k:])
v := ringDecodeAndDecompress4(b)
var mask nttElement // s⊺ ◦ NTT(u)
for i := range dx.s {
mask = polyAdd(mask, nttMul(dx.s[i], ntt(u[i])))
}
w := polySub(v, inverseNTT(mask))
return ringCompressAndEncode1(nil, w)
}
// fieldElement is an integer modulo q, an element of ℤ_q. It is always reduced.
type fieldElement uint16
// fieldCheckReduced checks that a value a is < q.
func fieldCheckReduced(a uint16) (fieldElement, error) {
if a >= q {
return 0, errors.New("unreduced field element")
}
return fieldElement(a), nil
}
// fieldReduceOnce reduces a value a < 2q.
func fieldReduceOnce(a uint16) fieldElement {
x := a - q
// If x underflowed, then x >= 2¹⁶ - q > 2¹⁵, so the top bit is set.
x += (x >> 15) * q
return fieldElement(x)
}
func fieldAdd(a, b fieldElement) fieldElement {
x := uint16(a + b)
return fieldReduceOnce(x)
}
func fieldSub(a, b fieldElement) fieldElement {
x := uint16(a - b + q)
return fieldReduceOnce(x)
}
const (
barrettMultiplier = 5039 // 2¹² * 2¹² / q
barrettShift = 24 // log₂(2¹² * 2¹²)
)
// fieldReduce reduces a value a < 2q² using Barrett reduction, to avoid
// potentially variable-time division.
func fieldReduce(a uint32) fieldElement {
quotient := uint32((uint64(a) * barrettMultiplier) >> barrettShift)
return fieldReduceOnce(uint16(a - quotient*q))
}
func fieldMul(a, b fieldElement) fieldElement {
x := uint32(a) * uint32(b)
return fieldReduce(x)
}
// fieldMulSub returns a * (b - c). This operation is fused to save a
// fieldReduceOnce after the subtraction.
func fieldMulSub(a, b, c fieldElement) fieldElement {
x := uint32(a) * uint32(b-c+q)
return fieldReduce(x)
}
// fieldAddMul returns a * b + c * d. This operation is fused to save a
// fieldReduceOnce and a fieldReduce.
func fieldAddMul(a, b, c, d fieldElement) fieldElement {
x := uint32(a) * uint32(b)
x += uint32(c) * uint32(d)
return fieldReduce(x)
}
// compress maps a field element uniformly to the range 0 to 2ᵈ-1, according to
// FIPS 203 (DRAFT), Definition 4.5.
func compress(x fieldElement, d uint8) uint16 {
// We want to compute (x * 2ᵈ) / q, rounded to nearest integer, with 1/2
// rounding up (see FIPS 203 (DRAFT), Section 2.3).
// Barrett reduction produces a quotient and a remainder in the range [0, 2q),
// such that dividend = quotient * q + remainder.
dividend := uint32(x) << d // x * 2ᵈ
quotient := uint32(uint64(dividend) * barrettMultiplier >> barrettShift)
remainder := dividend - quotient*q
// Since the remainder is in the range [0, 2q), not [0, q), we need to
// portion it into three spans for rounding.
//
// [ 0, q/2 ) -> round to 0
// [ q/2, q + q/2 ) -> round to 1
// [ q + q/2, 2q ) -> round to 2
//
// We can convert that to the following logic: add 1 if remainder > q/2,
// then add 1 again if remainder > q + q/2.
//
// Note that if remainder > x, then ⌊x⌋ - remainder underflows, and the top
// bit of the difference will be set.
quotient += (q/2 - remainder) >> 31 & 1
quotient += (q + q/2 - remainder) >> 31 & 1
// quotient might have overflowed at this point, so reduce it by masking.
var mask uint32 = (1 << d) - 1
return uint16(quotient & mask)
}
// decompress maps a number x between 0 and 2ᵈ-1 uniformly to the full range of
// field elements, according to FIPS 203 (DRAFT), Definition 4.6.
func decompress(y uint16, d uint8) fieldElement {
// We want to compute (y * q) / 2ᵈ, rounded to nearest integer, with 1/2
// rounding up (see FIPS 203 (DRAFT), Section 2.3).
dividend := uint32(y) * q
quotient := dividend >> d // (y * q) / 2ᵈ
// The d'th least-significant bit of the dividend (the most significant bit
// of the remainder) is 1 for the top half of the values that divide to the
// same quotient, which are the ones that round up.
quotient += dividend >> (d - 1) & 1
// quotient is at most (2¹¹-1) * q / 2¹¹ + 1 = 3328, so it didn't overflow.
return fieldElement(quotient)
}
// ringElement is a polynomial, an element of R_q, represented as an array
// according to FIPS 203 (DRAFT), Section 2.4.
type ringElement [n]fieldElement
// polyAdd adds two ringElements or nttElements.
func polyAdd[T ~[n]fieldElement](a, b T) (s T) {
for i := range s {
s[i] = fieldAdd(a[i], b[i])
}
return s
}
// polySub subtracts two ringElements or nttElements.
func polySub[T ~[n]fieldElement](a, b T) (s T) {
for i := range s {
s[i] = fieldSub(a[i], b[i])
}
return s
}
// polyByteEncode appends the 384-byte encoding of f to b.
//
// It implements ByteEncode₁₂, according to FIPS 203 (DRAFT), Algorithm 4.
func polyByteEncode[T ~[n]fieldElement](b []byte, f T) []byte {
out, B := sliceForAppend(b, encodingSize12)
for i := 0; i < n; i += 2 {
x := uint32(f[i]) | uint32(f[i+1])<<12
B[0] = uint8(x)
B[1] = uint8(x >> 8)
B[2] = uint8(x >> 16)
B = B[3:]
}
return out
}
// polyByteDecode decodes the 384-byte encoding of a polynomial, checking that
// all the coefficients are properly reduced. This achieves the "Modulus check"
// step of ML-KEM Encapsulation Input Validation.
//
// polyByteDecode is also used in ML-KEM Decapsulation, where the input
// validation is not required, but implicitly allowed by the specification.
//
// It implements ByteDecode₁₂, according to FIPS 203 (DRAFT), Algorithm 5.
func polyByteDecode[T ~[n]fieldElement](b []byte) (T, error) {
if len(b) != encodingSize12 {
return T{}, errors.New("mlkem768: invalid encoding length")
}
var f T
for i := 0; i < n; i += 2 {
d := uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16
const mask12 = 0b1111_1111_1111
var err error
if f[i], err = fieldCheckReduced(uint16(d & mask12)); err != nil {
return T{}, errors.New("mlkem768: invalid polynomial encoding")
}
if f[i+1], err = fieldCheckReduced(uint16(d >> 12)); err != nil {
return T{}, errors.New("mlkem768: invalid polynomial encoding")
}
b = b[3:]
}
return f, nil
}
// sliceForAppend takes a slice and a requested number of bytes. It returns a
// slice with the contents of the given slice followed by that many bytes and a
// second slice that aliases into it and contains only the extra bytes. If the
// original slice has sufficient capacity then no allocation is performed.
func sliceForAppend(in []byte, n int) (head, tail []byte) {
if total := len(in) + n; cap(in) >= total {
head = in[:total]
} else {
head = make([]byte, total)
copy(head, in)
}
tail = head[len(in):]
return
}
// ringCompressAndEncode1 appends a 32-byte encoding of a ring element to s,
// compressing one coefficients per bit.
//
// It implements Compress₁, according to FIPS 203 (DRAFT), Definition 4.5,
// followed by ByteEncode₁, according to FIPS 203 (DRAFT), Algorithm 4.
func ringCompressAndEncode1(s []byte, f ringElement) []byte {
s, b := sliceForAppend(s, encodingSize1)
for i := range b {
b[i] = 0
}
for i := range f {
b[i/8] |= uint8(compress(f[i], 1) << (i % 8))
}
return s
}
// ringDecodeAndDecompress1 decodes a 32-byte slice to a ring element where each
// bit is mapped to 0 or ⌈q/2⌋.
//
// It implements ByteDecode₁, according to FIPS 203 (DRAFT), Algorithm 5,
// followed by Decompress₁, according to FIPS 203 (DRAFT), Definition 4.6.
func ringDecodeAndDecompress1(b *[encodingSize1]byte) ringElement {
var f ringElement
for i := range f {
b_i := b[i/8] >> (i % 8) & 1
const halfQ = (q + 1) / 2 // ⌈q/2⌋, rounded up per FIPS 203 (DRAFT), Section 2.3
f[i] = fieldElement(b_i) * halfQ // 0 decompresses to 0, and 1 to ⌈q/2⌋
}
return f
}
// ringCompressAndEncode4 appends a 128-byte encoding of a ring element to s,
// compressing two coefficients per byte.
//
// It implements Compress₄, according to FIPS 203 (DRAFT), Definition 4.5,
// followed by ByteEncode₄, according to FIPS 203 (DRAFT), Algorithm 4.
func ringCompressAndEncode4(s []byte, f ringElement) []byte {
s, b := sliceForAppend(s, encodingSize4)
for i := 0; i < n; i += 2 {
b[i/2] = uint8(compress(f[i], 4) | compress(f[i+1], 4)<<4)
}
return s
}
// ringDecodeAndDecompress4 decodes a 128-byte encoding of a ring element where
// each four bits are mapped to an equidistant distribution.
//
// It implements ByteDecode₄, according to FIPS 203 (DRAFT), Algorithm 5,
// followed by Decompress₄, according to FIPS 203 (DRAFT), Definition 4.6.
func ringDecodeAndDecompress4(b *[encodingSize4]byte) ringElement {
var f ringElement
for i := 0; i < n; i += 2 {
f[i] = fieldElement(decompress(uint16(b[i/2]&0b1111), 4))
f[i+1] = fieldElement(decompress(uint16(b[i/2]>>4), 4))
}
return f
}
// ringCompressAndEncode10 appends a 320-byte encoding of a ring element to s,
// compressing four coefficients per five bytes.
//
// It implements Compress₁₀, according to FIPS 203 (DRAFT), Definition 4.5,
// followed by ByteEncode₁₀, according to FIPS 203 (DRAFT), Algorithm 4.
func ringCompressAndEncode10(s []byte, f ringElement) []byte {
s, b := sliceForAppend(s, encodingSize10)
for i := 0; i < n; i += 4 {
var x uint64
x |= uint64(compress(f[i+0], 10))
x |= uint64(compress(f[i+1], 10)) << 10
x |= uint64(compress(f[i+2], 10)) << 20
x |= uint64(compress(f[i+3], 10)) << 30
b[0] = uint8(x)
b[1] = uint8(x >> 8)
b[2] = uint8(x >> 16)
b[3] = uint8(x >> 24)
b[4] = uint8(x >> 32)
b = b[5:]
}
return s
}
// ringDecodeAndDecompress10 decodes a 320-byte encoding of a ring element where
// each ten bits are mapped to an equidistant distribution.
//
// It implements ByteDecode₁₀, according to FIPS 203 (DRAFT), Algorithm 5,
// followed by Decompress₁₀, according to FIPS 203 (DRAFT), Definition 4.6.
func ringDecodeAndDecompress10(bb *[encodingSize10]byte) ringElement {
b := bb[:]
var f ringElement
for i := 0; i < n; i += 4 {
x := uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 | uint64(b[4])<<32
b = b[5:]
f[i] = fieldElement(decompress(uint16(x>>0&0b11_1111_1111), 10))
f[i+1] = fieldElement(decompress(uint16(x>>10&0b11_1111_1111), 10))
f[i+2] = fieldElement(decompress(uint16(x>>20&0b11_1111_1111), 10))
f[i+3] = fieldElement(decompress(uint16(x>>30&0b11_1111_1111), 10))
}
return f
}
// samplePolyCBD draws a ringElement from the special Dη distribution given a
// stream of random bytes generated by the PRF function, according to FIPS 203
// (DRAFT), Algorithm 7 and Definition 4.1.
func samplePolyCBD(s []byte, b byte) ringElement {
prf := sha3.NewShake256()
prf.Write(s)
prf.Write([]byte{b})
B := make([]byte, 128)
prf.Read(B)
// SamplePolyCBD simply draws four (2η) bits for each coefficient, and adds
// the first two and subtracts the last two.
var f ringElement
for i := 0; i < n; i += 2 {
b := B[i/2]
b_7, b_6, b_5, b_4 := b>>7, b>>6&1, b>>5&1, b>>4&1
b_3, b_2, b_1, b_0 := b>>3&1, b>>2&1, b>>1&1, b&1
f[i] = fieldSub(fieldElement(b_0+b_1), fieldElement(b_2+b_3))
f[i+1] = fieldSub(fieldElement(b_4+b_5), fieldElement(b_6+b_7))
}
return f
}
// nttElement is an NTT representation, an element of T_q, represented as an
// array according to FIPS 203 (DRAFT), Section 2.4.
type nttElement [n]fieldElement
// gammas are the values ζ^2BitRev7(i)+1 mod q for each index i.
var gammas = [128]fieldElement{17, 3312, 2761, 568, 583, 2746, 2649, 680, 1637, 1692, 723, 2606, 2288, 1041, 1100, 2229, 1409, 1920, 2662, 667, 3281, 48, 233, 3096, 756, 2573, 2156, 1173, 3015, 314, 3050, 279, 1703, 1626, 1651, 1678, 2789, 540, 1789, 1540, 1847, 1482, 952, 2377, 1461, 1868, 2687, 642, 939, 2390, 2308, 1021, 2437, 892, 2388, 941, 733, 2596, 2337, 992, 268, 3061, 641, 2688, 1584, 1745, 2298, 1031, 2037, 1292, 3220, 109, 375, 2954, 2549, 780, 2090, 1239, 1645, 1684, 1063, 2266, 319, 3010, 2773, 556, 757, 2572, 2099, 1230, 561, 2768, 2466, 863, 2594, 735, 2804, 525, 1092, 2237, 403, 2926, 1026, 2303, 1143, 2186, 2150, 1179, 2775, 554, 886, 2443, 1722, 1607, 1212, 2117, 1874, 1455, 1029, 2300, 2110, 1219, 2935, 394, 885, 2444, 2154, 1175}
// nttMul multiplies two nttElements.
//
// It implements MultiplyNTTs, according to FIPS 203 (DRAFT), Algorithm 10.
func nttMul(f, g nttElement) nttElement {
var h nttElement
// We use i += 2 for bounds check elimination. See https://go.dev/issue/66826.
for i := 0; i < 256; i += 2 {
a0, a1 := f[i], f[i+1]
b0, b1 := g[i], g[i+1]
h[i] = fieldAddMul(a0, b0, fieldMul(a1, b1), gammas[i/2])
h[i+1] = fieldAddMul(a0, b1, a1, b0)
}
return h
}
// zetas are the values ζ^BitRev7(k) mod q for each index k.
var zetas = [128]fieldElement{1, 1729, 2580, 3289, 2642, 630, 1897, 848, 1062, 1919, 193, 797, 2786, 3260, 569, 1746, 296, 2447, 1339, 1476, 3046, 56, 2240, 1333, 1426, 2094, 535, 2882, 2393, 2879, 1974, 821, 289, 331, 3253, 1756, 1197, 2304, 2277, 2055, 650, 1977, 2513, 632, 2865, 33, 1320, 1915, 2319, 1435, 807, 452, 1438, 2868, 1534, 2402, 2647, 2617, 1481, 648, 2474, 3110, 1227, 910, 17, 2761, 583, 2649, 1637, 723, 2288, 1100, 1409, 2662, 3281, 233, 756, 2156, 3015, 3050, 1703, 1651, 2789, 1789, 1847, 952, 1461, 2687, 939, 2308, 2437, 2388, 733, 2337, 268, 641, 1584, 2298, 2037, 3220, 375, 2549, 2090, 1645, 1063, 319, 2773, 757, 2099, 561, 2466, 2594, 2804, 1092, 403, 1026, 1143, 2150, 2775, 886, 1722, 1212, 1874, 1029, 2110, 2935, 885, 2154}
// ntt maps a ringElement to its nttElement representation.
//
// It implements NTT, according to FIPS 203 (DRAFT), Algorithm 8.
func ntt(f ringElement) nttElement {
k := 1
for len := 128; len >= 2; len /= 2 {
for start := 0; start < 256; start += 2 * len {
zeta := zetas[k]
k++
// Bounds check elimination hint.
f, flen := f[start:start+len], f[start+len:start+len+len]
for j := 0; j < len; j++ {
t := fieldMul(zeta, flen[j])
flen[j] = fieldSub(f[j], t)
f[j] = fieldAdd(f[j], t)
}
}
}
return nttElement(f)
}
// inverseNTT maps a nttElement back to the ringElement it represents.
//
// It implements NTT⁻¹, according to FIPS 203 (DRAFT), Algorithm 9.
func inverseNTT(f nttElement) ringElement {
k := 127
for len := 2; len <= 128; len *= 2 {
for start := 0; start < 256; start += 2 * len {
zeta := zetas[k]
k--
// Bounds check elimination hint.
f, flen := f[start:start+len], f[start+len:start+len+len]
for j := 0; j < len; j++ {
t := f[j]
f[j] = fieldAdd(t, flen[j])
flen[j] = fieldMulSub(zeta, flen[j], t)
}
}
}
for i := range f {
f[i] = fieldMul(f[i], 3303) // 3303 = 128⁻¹ mod q
}
return ringElement(f)
}
// sampleNTT draws a uniformly random nttElement from a stream of uniformly
// random bytes generated by the XOF function, according to FIPS 203 (DRAFT),
// Algorithm 6 and Definition 4.2.
func sampleNTT(rho []byte, ii, jj byte) nttElement {
B := sha3.NewShake128()
B.Write(rho)
B.Write([]byte{ii, jj})
// SampleNTT essentially draws 12 bits at a time from r, interprets them in
// little-endian, and rejects values higher than q, until it drew 256
// values. (The rejection rate is approximately 19%.)
//
// To do this from a bytes stream, it draws three bytes at a time, and
// splits them into two uint16 appropriately masked.
//
// r₀ r₁ r₂
// |- - - - - - - -|- - - - - - - -|- - - - - - - -|
//
// Uint16(r₀ || r₁)
// |- - - - - - - - - - - - - - - -|
// |- - - - - - - - - - - -|
// d₁
//
// Uint16(r₁ || r₂)
// |- - - - - - - - - - - - - - - -|
// |- - - - - - - - - - - -|
// d₂
//
// Note that in little-endian, the rightmost bits are the most significant
// bits (dropped with a mask) and the leftmost bits are the least
// significant bits (dropped with a right shift).
var a nttElement
var j int // index into a
var buf [24]byte // buffered reads from B
off := len(buf) // index into buf, starts in a "buffer fully consumed" state
for {
if off >= len(buf) {
B.Read(buf[:])
off = 0
}
d1 := binary.LittleEndian.Uint16(buf[off:]) & 0b1111_1111_1111
d2 := binary.LittleEndian.Uint16(buf[off+1:]) >> 4
off += 3
if d1 < q {
a[j] = fieldElement(d1)
j++
}
if j >= len(a) {
break
}
if d2 < q {
a[j] = fieldElement(d2)
j++
}
if j >= len(a) {
break
}
}
return a
}

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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package randutil contains internal randomness utilities for various
// crypto packages.
package randutil
import (
"io"
"math/rand/v2"
)
// MaybeReadByte reads a single byte from r with 50% probability. This is used
// to ensure that callers do not depend on non-guaranteed behaviour, e.g.
// assuming that rsa.GenerateKey is deterministic w.r.t. a given random stream.
//
// This does not affect tests that pass a stream of fixed bytes as the random
// source (e.g. a zeroReader).
func MaybeReadByte(r io.Reader) {
if rand.Uint64()&1 == 1 {
return
}
var buf [1]byte
r.Read(buf[:])
}

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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package sha3
import (
"bytes"
//"crypto/internal/fips140"
"github.com/xtls/reality/byteorder"
"errors"
"math/bits"
)
type SHAKE struct {
d Digest // SHA-3 state context and Read/Write operations
// initBlock is the cSHAKE specific initialization set of bytes. It is initialized
// by newCShake function and stores concatenation of N followed by S, encoded
// by the method specified in 3.3 of [1].
// It is stored here in order for Reset() to be able to put context into
// initial state.
initBlock []byte
}
func bytepad(data []byte, rate int) []byte {
out := make([]byte, 0, 9+len(data)+rate-1)
out = append(out, leftEncode(uint64(rate))...)
out = append(out, data...)
if padlen := rate - len(out)%rate; padlen < rate {
out = append(out, make([]byte, padlen)...)
}
return out
}
func leftEncode(x uint64) []byte {
// Let n be the smallest positive integer for which 2^(8n) > x.
n := (bits.Len64(x) + 7) / 8
if n == 0 {
n = 1
}
// Return n || x with n as a byte and x an n bytes in big-endian order.
b := make([]byte, 9)
byteorder.BEPutUint64(b[1:], x)
b = b[9-n-1:]
b[0] = byte(n)
return b
}
func newCShake(N, S []byte, rate, outputLen int, dsbyte byte) *SHAKE {
c := &SHAKE{d: Digest{rate: rate, outputLen: outputLen, dsbyte: dsbyte}}
c.initBlock = make([]byte, 0, 9+len(N)+9+len(S)) // leftEncode returns max 9 bytes
c.initBlock = append(c.initBlock, leftEncode(uint64(len(N))*8)...)
c.initBlock = append(c.initBlock, N...)
c.initBlock = append(c.initBlock, leftEncode(uint64(len(S))*8)...)
c.initBlock = append(c.initBlock, S...)
c.Write(bytepad(c.initBlock, c.d.rate))
return c
}
func (s *SHAKE) BlockSize() int { return s.d.BlockSize() }
func (s *SHAKE) Size() int { return s.d.Size() }
// Sum appends a portion of output to b and returns the resulting slice. The
// output length is selected to provide full-strength generic security: 32 bytes
// for SHAKE128 and 64 bytes for SHAKE256. It does not change the underlying
// state. It panics if any output has already been read.
func (s *SHAKE) Sum(in []byte) []byte { return s.d.Sum(in) }
// Write absorbs more data into the hash's state.
// It panics if any output has already been read.
func (s *SHAKE) Write(p []byte) (n int, err error) { return s.d.Write(p) }
func (s *SHAKE) Read(out []byte) (n int, err error) {
//fips140.RecordApproved()
// Note that read is not exposed on Digest since SHA-3 does not offer
// variable output length. It is only used internally by Sum.
return s.d.read(out)
}
// Reset resets the hash to initial state.
func (s *SHAKE) Reset() {
s.d.Reset()
if len(s.initBlock) != 0 {
s.Write(bytepad(s.initBlock, s.d.rate))
}
}
// Clone returns a copy of the SHAKE context in its current state.
func (s *SHAKE) Clone() *SHAKE {
ret := *s
return &ret
}
func (s *SHAKE) MarshalBinary() ([]byte, error) {
return s.AppendBinary(make([]byte, 0, marshaledSize+len(s.initBlock)))
}
func (s *SHAKE) AppendBinary(b []byte) ([]byte, error) {
b, err := s.d.AppendBinary(b)
if err != nil {
return nil, err
}
b = append(b, s.initBlock...)
return b, nil
}
func (s *SHAKE) UnmarshalBinary(b []byte) error {
if len(b) < marshaledSize {
return errors.New("sha3: invalid hash state")
}
if err := s.d.UnmarshalBinary(b[:marshaledSize]); err != nil {
return err
}
s.initBlock = bytes.Clone(b[marshaledSize:])
return nil
}
// NewShake128 creates a new SHAKE128 XOF.
func NewShake128() *SHAKE {
return &SHAKE{d: Digest{rate: rateK256, outputLen: 32, dsbyte: dsbyteShake}}
}
// NewShake256 creates a new SHAKE256 XOF.
func NewShake256() *SHAKE {
return &SHAKE{d: Digest{rate: rateK512, outputLen: 64, dsbyte: dsbyteShake}}
}
// NewCShake128 creates a new cSHAKE128 XOF.
//
// N is used to define functions based on cSHAKE, it can be empty when plain
// cSHAKE is desired. S is a customization byte string used for domain
// separation. When N and S are both empty, this is equivalent to NewShake128.
func NewCShake128(N, S []byte) *SHAKE {
if len(N) == 0 && len(S) == 0 {
return NewShake128()
}
return newCShake(N, S, rateK256, 32, dsbyteCShake)
}
// NewCShake256 creates a new cSHAKE256 XOF.
//
// N is used to define functions based on cSHAKE, it can be empty when plain
// cSHAKE is desired. S is a customization byte string used for domain
// separation. When N and S are both empty, this is equivalent to NewShake256.
func NewCShake256(N, S []byte) *SHAKE {
if len(N) == 0 && len(S) == 0 {
return NewShake256()
}
return newCShake(N, S, rateK512, 64, dsbyteCShake)
}