diff --git a/auth.go b/auth.go
index d595925..c389cd4 100644
--- a/auth.go
+++ b/auth.go
@@ -15,6 +15,8 @@ import (
 	"fmt"
 	"hash"
 	"io"
+
+	"github.com/xtls/reality/fips140tls"
 )
 
 // verifyHandshakeSignature verifies a signature against pre-hashed
@@ -242,7 +244,7 @@ func selectSignatureScheme(vers uint16, c *Certificate, peerAlgs []SignatureSche
 	// Pick signature scheme in the peer's preference order, as our
 	// preference order is not configurable.
 	for _, preferredAlg := range peerAlgs {
-		if needFIPS() && !isSupportedSignatureAlgorithm(preferredAlg, defaultSupportedSignatureAlgorithmsFIPS) {
+		if fips140tls.Required() && !isSupportedSignatureAlgorithm(preferredAlg, defaultSupportedSignatureAlgorithmsFIPS) {
 			continue
 		}
 		if isSupportedSignatureAlgorithm(preferredAlg, supportedAlgs) {
diff --git a/common.go b/common.go
index 895ee85..61381c9 100644
--- a/common.go
+++ b/common.go
@@ -25,6 +25,8 @@ import (
 	"sync"
 	"time"
 	_ "unsafe" // for linkname
+
+	"github.com/xtls/reality/fips140tls"
 )
 
 const (
@@ -1085,12 +1087,12 @@ func (c *Config) time() time.Time {
 
 func (c *Config) cipherSuites() []uint16 {
 	if c.CipherSuites == nil {
-		if needFIPS() {
+		if fips140tls.Required() {
 			return defaultCipherSuitesFIPS
 		}
 		return defaultCipherSuites()
 	}
-	if needFIPS() {
+	if fips140tls.Required() {
 		cipherSuites := slices.Clone(c.CipherSuites)
 		return slices.DeleteFunc(cipherSuites, func(id uint16) bool {
 			return !slices.Contains(defaultCipherSuitesFIPS, id)
@@ -1114,7 +1116,7 @@ const roleServer = false
 func (c *Config) supportedVersions(isClient bool) []uint16 {
 	versions := make([]uint16, 0, len(supportedVersions))
 	for _, v := range supportedVersions {
-		if needFIPS() && !slices.Contains(defaultSupportedVersionsFIPS, v) {
+		if fips140tls.Required() && !slices.Contains(defaultSupportedVersionsFIPS, v) {
 			continue
 		}
 		if (c == nil || c.MinVersion == 0) && v < VersionTLS12 {
@@ -1160,12 +1162,12 @@ func (c *Config) curvePreferences(version uint16) []CurveID {
 	var curvePreferences []CurveID
 	if c != nil && len(c.CurvePreferences) != 0 {
 		curvePreferences = slices.Clone(c.CurvePreferences)
-		if needFIPS() {
+		if fips140tls.Required() {
 			return slices.DeleteFunc(curvePreferences, func(c CurveID) bool {
 				return !slices.Contains(defaultCurvePreferencesFIPS, c)
 			})
 		}
-	} else if needFIPS() {
+	} else if fips140tls.Required() {
 		curvePreferences = slices.Clone(defaultCurvePreferencesFIPS)
 	} else {
 		curvePreferences = defaultCurvePreferences()
@@ -1637,7 +1639,7 @@ func unexpectedMessageError(wanted, got any) error {
 
 // supportedSignatureAlgorithms returns the supported signature algorithms.
 func supportedSignatureAlgorithms() []SignatureScheme {
-	if !needFIPS() {
+	if !fips140tls.Required() {
 		return defaultSupportedSignatureAlgorithms
 	}
 	return defaultSupportedSignatureAlgorithmsFIPS
@@ -1666,3 +1668,56 @@ func (e *CertificateVerificationError) Error() string {
 func (e *CertificateVerificationError) Unwrap() error {
 	return e.Err
 }
+
+// fipsAllowedChains returns chains that are allowed to be used in a TLS connection
+// based on the current fips140tls enforcement setting.
+//
+// If fips140tls is not required, the chains are returned as-is with no processing.
+// Otherwise, the returned chains are filtered to only those allowed by FIPS 140-3.
+// If this results in no chains it returns an error.
+func fipsAllowedChains(chains [][]*x509.Certificate) ([][]*x509.Certificate, error) {
+	if !fips140tls.Required() {
+		return chains, nil
+	}
+
+	permittedChains := make([][]*x509.Certificate, 0, len(chains))
+	for _, chain := range chains {
+		if fipsAllowChain(chain) {
+			permittedChains = append(permittedChains, chain)
+		}
+	}
+
+	if len(permittedChains) == 0 {
+		return nil, errors.New("tls: no FIPS compatible certificate chains found")
+	}
+
+	return permittedChains, nil
+}
+
+func fipsAllowChain(chain []*x509.Certificate) bool {
+	if len(chain) == 0 {
+		return false
+	}
+
+	for _, cert := range chain {
+		if !fipsAllowCert(cert) {
+			return false
+		}
+	}
+
+	return true
+}
+
+func fipsAllowCert(c *x509.Certificate) bool {
+	// The key must be RSA 2048, RSA 3072, RSA 4096,
+	// or ECDSA P-256, P-384, P-521.
+	switch k := c.PublicKey.(type) {
+	case *rsa.PublicKey:
+		size := k.N.BitLen()
+		return size == 2048 || size == 3072 || size == 4096
+	case *ecdsa.PublicKey:
+		return k.Curve == elliptic.P256() || k.Curve == elliptic.P384() || k.Curve == elliptic.P521()
+	}
+
+	return false
+}
\ No newline at end of file
diff --git a/defaults.go b/defaults.go
index 19dc10e..f2d9ff3 100644
--- a/defaults.go
+++ b/defaults.go
@@ -89,7 +89,9 @@ var defaultCipherSuitesTLS13NoAES = []uint16{
 	TLS_AES_256_GCM_SHA384,
 }
 
-// The FIPS-only policies below match BoringSSL's ssl_policy_fips_202205.
+// The FIPS-only policies below match BoringSSL's
+// ssl_compliance_policy_fips_202205, which is based on NIST SP 800-52r2.
+// https://cs.opensource.google/boringssl/boringssl/+/master:ssl/ssl_lib.cc;l=3289;drc=ea7a88fa
 
 var defaultSupportedVersionsFIPS = []uint16{
 	VersionTLS12,
diff --git a/drbg/rand.go b/drbg/rand.go
index 7fe0b57..a3255fe 100644
--- a/drbg/rand.go
+++ b/drbg/rand.go
@@ -14,6 +14,7 @@ import (
 	"github.com/xtls/reality/randutil"
 	// "github.com/xtls/reality/sysrand"
 	
+	"crypto/fips140"
 	"crypto/rand"
 	"io"
 	"sync"
@@ -33,10 +34,10 @@ var drbgs = sync.Pool{
 // 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
-	// }
+	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.
diff --git a/fips140tls/fipstls.go b/fips140tls/fipstls.go
new file mode 100644
index 0000000..3cf9b0f
--- /dev/null
+++ b/fips140tls/fipstls.go
@@ -0,0 +1,37 @@
+// 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 fips140tls controls whether crypto/tls requires FIPS-approved settings.
+package fips140tls
+
+import (
+	"crypto/fips140"
+	"sync/atomic"
+)
+
+var required atomic.Bool
+
+func init() {
+	if fips140.Enabled() {
+		Force()
+	}
+}
+
+// Force forces crypto/tls to restrict TLS configurations to FIPS-approved settings.
+// By design, this call is impossible to undo (except in tests).
+func Force() {
+	required.Store(true)
+}
+
+// Required reports whether FIPS-approved settings are required.
+//
+// Required is true if FIPS 140-3 mode is enabled with GODEBUG=fips140=on, or if
+// the crypto/tls/fipsonly package is imported by a Go+BoringCrypto build.
+func Required() bool {
+	return required.Load()
+}
+
+func TestingOnlyAbandon() {
+	required.Store(false)
+}
\ No newline at end of file
diff --git a/go.mod b/go.mod
index f3e384f..ca25db1 100644
--- a/go.mod
+++ b/go.mod
@@ -1,9 +1,9 @@
 module github.com/xtls/reality
 
-go 1.23
+go 1.24
 
 require (
-	github.com/pires/go-proxyproto v0.7.0
-	golang.org/x/crypto v0.26.0
-	golang.org/x/sys v0.24.0
+	github.com/pires/go-proxyproto v0.8.1
+	golang.org/x/crypto v0.37.0
+	golang.org/x/sys v0.32.0
 )
diff --git a/go.sum b/go.sum
index 68bcfd9..be439aa 100644
--- a/go.sum
+++ b/go.sum
@@ -1,6 +1,12 @@
 github.com/pires/go-proxyproto v0.7.0 h1:IukmRewDQFWC7kfnb66CSomk2q/seBuilHBYFwyq0Hs=
 github.com/pires/go-proxyproto v0.7.0/go.mod h1:Vz/1JPY/OACxWGQNIRY2BeyDmpoaWmEP40O9LbuiFR4=
+github.com/pires/go-proxyproto v0.8.1 h1:9KEixbdJfhrbtjpz/ZwCdWDD2Xem0NZ38qMYaASJgp0=
+github.com/pires/go-proxyproto v0.8.1/go.mod h1:ZKAAyp3cgy5Y5Mo4n9AlScrkCZwUy0g3Jf+slqQVcuU=
 golang.org/x/crypto v0.26.0 h1:RrRspgV4mU+YwB4FYnuBoKsUapNIL5cohGAmSH3azsw=
 golang.org/x/crypto v0.26.0/go.mod h1:GY7jblb9wI+FOo5y8/S2oY4zWP07AkOJ4+jxCqdqn54=
+golang.org/x/crypto v0.37.0 h1:kJNSjF/Xp7kU0iB2Z+9viTPMW4EqqsrywMXLJOOsXSE=
+golang.org/x/crypto v0.37.0/go.mod h1:vg+k43peMZ0pUMhYmVAWysMK35e6ioLh3wB8ZCAfbVc=
 golang.org/x/sys v0.24.0 h1:Twjiwq9dn6R1fQcyiK+wQyHWfaz/BJB+YIpzU/Cv3Xg=
 golang.org/x/sys v0.24.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+golang.org/x/sys v0.32.0 h1:s77OFDvIQeibCmezSnk/q6iAfkdiQaJi4VzroCFrN20=
+golang.org/x/sys v0.32.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
diff --git a/handshake_client.go b/handshake_client.go
index e6a9420..781cfb7 100644
--- a/handshake_client.go
+++ b/handshake_client.go
@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"github.com/xtls/reality/byteorder"
+	"github.com/xtls/reality/fips140tls"
 	"github.com/xtls/reality/hpke"
 	"github.com/xtls/reality/mlkem"
 	"github.com/xtls/reality/tls13"
@@ -142,7 +143,7 @@ func (c *Conn) makeClientHello() (*clientHelloMsg, *keySharePrivateKeys, *echCon
 		if len(hello.supportedVersions) == 1 {
 			hello.cipherSuites = nil
 		}
-		if needFIPS() {
+		if fips140tls.Required() {
 			hello.cipherSuites = append(hello.cipherSuites, defaultCipherSuitesTLS13FIPS...)
 		} else if hasAESGCMHardwareSupport {
 			hello.cipherSuites = append(hello.cipherSuites, defaultCipherSuitesTLS13...)
@@ -1105,8 +1106,13 @@ func (c *Conn) verifyServerCertificate(certificates [][]byte) error {
 			for _, cert := range certs[1:] {
 				opts.Intermediates.AddCert(cert)
 			}
-			var err error
-			c.verifiedChains, err = certs[0].Verify(opts)
+			chains, err := certs[0].Verify(opts)
+			if err != nil {
+				c.sendAlert(alertBadCertificate)
+				return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
+			}
+
+			c.verifiedChains, err = fipsAllowedChains(chains)
 			if err != nil {
 				c.sendAlert(alertBadCertificate)
 				return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
@@ -1123,8 +1129,13 @@ func (c *Conn) verifyServerCertificate(certificates [][]byte) error {
 		for _, cert := range certs[1:] {
 			opts.Intermediates.AddCert(cert)
 		}
-		var err error
-		c.verifiedChains, err = certs[0].Verify(opts)
+		chains, err := certs[0].Verify(opts)
+		if err != nil {
+			c.sendAlert(alertBadCertificate)
+			return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
+		}
+
+		c.verifiedChains, err = fipsAllowedChains(chains)
 		if err != nil {
 			c.sendAlert(alertBadCertificate)
 			return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
diff --git a/handshake_server.go b/handshake_server.go
index 3201520..6958c95 100644
--- a/handshake_server.go
+++ b/handshake_server.go
@@ -910,7 +910,11 @@ func (c *Conn) processCertsFromClient(certificate Certificate) error {
 			return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
 		}
 
-		c.verifiedChains = chains
+		c.verifiedChains, err = fipsAllowedChains(chains)
+		if err != nil {
+			c.sendAlert(alertBadCertificate)
+			return &CertificateVerificationError{UnverifiedCertificates: certs, Err: err}
+		}
 	}
 
 	c.peerCertificates = certs
diff --git a/handshake_server_tls13.go b/handshake_server_tls13.go
index 3f0f465..be75a1f 100644
--- a/handshake_server_tls13.go
+++ b/handshake_server_tls13.go
@@ -22,6 +22,7 @@ import (
 	"time"
 
 	"github.com/xtls/reality/byteorder"
+	"github.com/xtls/reality/fips140tls"
 	"github.com/xtls/reality/mlkem"
 	"github.com/xtls/reality/tls13"
 )
@@ -215,7 +216,7 @@ func (hs *serverHandshakeStateTLS13) processClientHello() error {
 	if !hasAESGCMHardwareSupport || !aesgcmPreferred(hs.clientHello.cipherSuites) {
 		preferenceList = defaultCipherSuitesTLS13NoAES
 	}
-	if needFIPS() {
+	if fips140tls.Required() {
 		preferenceList = defaultCipherSuitesTLS13FIPS
 	}
 	for _, suiteID := range preferenceList {
diff --git a/notboring.go b/notboring.go
deleted file mode 100644
index 5fe954f..0000000
--- a/notboring.go
+++ /dev/null
@@ -1,9 +0,0 @@
-// Copyright 2022 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-Go file.
-
-//go:build !boringcrypto
-
-package reality
-
-func needFIPS() bool { return false }