crypto/internal/fips/tls12: implement TLS 1.2 KDF

For #69536

Change-Id: If2477c5249a7c7db45c1af05e715ae0b61e7d940
Reviewed-on: https://go-review.googlesource.com/c/go/+/626837
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Daniel McCarney <daniel@binaryparadox.net>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>

src/crypto/internal/fips/cast_external_test.go

@@ -18,6 +18,7 @@ import (
 	_ "crypto/internal/fips/sha256"
 	_ "crypto/internal/fips/sha3"
 	_ "crypto/internal/fips/sha512"
+	_ "crypto/internal/fips/tls12"
 	_ "crypto/internal/fips/tls13"
 )
 

src/crypto/internal/fips/tls12/cast.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 tls12
+
+import (
+	"bytes"
+	"crypto/internal/fips"
+	"crypto/internal/fips/sha256"
+	"errors"
+)
+
+func init() {
+	fips.CAST("TLSv1.2-SHA2-256", func() error {
+		input := []byte{
+			0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+			0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, 0x10,
+		}
+		transcript := []byte{
+			0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
+			0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, 0x20,
+		}
+		want := []byte{
+			0x8c, 0x3e, 0xed, 0xa7, 0x1c, 0x1b, 0x4c, 0xc0,
+			0xa0, 0x44, 0x90, 0x75, 0xa8, 0x8e, 0xbc, 0x7c,
+			0x5e, 0x1c, 0x4b, 0x1e, 0x4f, 0xe3, 0xc1, 0x06,
+			0xeb, 0xdc, 0xc0, 0x5d, 0xc0, 0xc8, 0xec, 0xf3,
+			0xe2, 0xb9, 0xd1, 0x03, 0x5e, 0xb2, 0x60, 0x5d,
+			0x12, 0x68, 0x4f, 0x49, 0xdf, 0xa9, 0x9d, 0xcc,
+		}
+		if got := MasterSecret(sha256.New, input, transcript); !bytes.Equal(got, want) {
+			return errors.New("unexpected result")
+		}
+		return nil
+	})
+}

src/crypto/internal/fips/tls12/tls12.go

@@ -0,0 +1,69 @@
+// 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 tls12
+
+import (
+	"crypto/internal/fips"
+	"crypto/internal/fips/hmac"
+	"crypto/internal/fips/sha256"
+	"crypto/internal/fips/sha512"
+)
+
+// PRF implements the TLS 1.2 pseudo-random function, as defined in RFC 5246,
+// Section 5 and allowed by SP 800-135, Revision 1, Section 4.2.2.
+func PRF[H fips.Hash](hash func() H, secret []byte, label string, seed []byte, keyLen int) []byte {
+	labelAndSeed := make([]byte, len(label)+len(seed))
+	copy(labelAndSeed, label)
+	copy(labelAndSeed[len(label):], seed)
+
+	result := make([]byte, keyLen)
+	pHash(hash, result, secret, labelAndSeed)
+	return result
+}
+
+// pHash implements the P_hash function, as defined in RFC 5246, Section 5.
+func pHash[H fips.Hash](hash func() H, result, secret, seed []byte) {
+	h := hmac.New(hash, secret)
+	h.Write(seed)
+	a := h.Sum(nil)
+
+	for len(result) > 0 {
+		h.Reset()
+		h.Write(a)
+		h.Write(seed)
+		b := h.Sum(nil)
+		n := copy(result, b)
+		result = result[n:]
+
+		h.Reset()
+		h.Write(a)
+		a = h.Sum(nil)
+	}
+}
+
+const masterSecretLength = 48
+const extendedMasterSecretLabel = "extended master secret"
+
+// MasterSecret implements the TLS 1.2 extended master secret derivation, as
+// defined in RFC 7627 and allowed by SP 800-135, Revision 1, Section 4.2.2.
+func MasterSecret[H fips.Hash](hash func() H, preMasterSecret, transcript []byte) []byte {
+	// "The TLS 1.2 KDF is an approved KDF when the following conditions are
+	// satisfied: [...] (3) P_HASH uses either SHA-256, SHA-384 or SHA-512."
+	h := hash()
+	switch any(h).(type) {
+	case *sha256.Digest:
+		if h.Size() != 32 {
+			fips.RecordNonApproved()
+		}
+	case *sha512.Digest:
+		if h.Size() != 46 && h.Size() != 64 {
+			fips.RecordNonApproved()
+		}
+	default:
+		fips.RecordNonApproved()
+	}
+
+	return PRF(hash, preMasterSecret, extendedMasterSecretLabel, transcript, masterSecretLength)
+}

src/crypto/tls/prf.go

@@ -7,6 +7,7 @@ package tls
 import (
 	"crypto"
 	"crypto/hmac"
+	"crypto/internal/fips/tls12"
 	"crypto/md5"
 	"crypto/sha1"
 	"crypto/sha256"
@@ -16,6 +17,8 @@ import (
 	"hash"
 )
 
+type prfFunc func(secret []byte, label string, seed []byte, keyLen int) []byte
+
 // Split a premaster secret in two as specified in RFC 4346, Section 5.
 func splitPreMasterSecret(secret []byte) (s1, s2 []byte) {
 	s1 = secret[0 : (len(secret)+1)/2]
@@ -45,7 +48,8 @@ func pHash(result, secret, seed []byte, hash func() hash.Hash) {
 }
 
 // prf10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, Section 5.
-func prf10(result, secret, label, seed []byte) {
+func prf10(secret []byte, label string, seed []byte, keyLen int) []byte {
+	result := make([]byte, keyLen)
 	hashSHA1 := sha1.New
 	hashMD5 := md5.New
 
@@ -61,16 +65,14 @@ func prf10(result, secret, label, seed []byte) {
 	for i, b := range result2 {
 		result[i] ^= b
 	}
+
+	return result
 }
 
 // prf12 implements the TLS 1.2 pseudo-random function, as defined in RFC 5246, Section 5.
-func prf12(hashFunc func() hash.Hash) func(result, secret, label, seed []byte) {
-	return func(result, secret, label, seed []byte) {
-		labelAndSeed := make([]byte, len(label)+len(seed))
-		copy(labelAndSeed, label)
-		copy(labelAndSeed[len(label):], seed)
-
-		pHash(result, secret, labelAndSeed, hashFunc)
+func prf12(hashFunc func() hash.Hash) prfFunc {
+	return func(secret []byte, label string, seed []byte, keyLen int) []byte {
+		return tls12.PRF(hashFunc, secret, label, seed, keyLen)
 	}
 }
 
@@ -79,13 +81,13 @@ const (
 	finishedVerifyLength = 12 // Length of verify_data in a Finished message.
 )
 
-var masterSecretLabel = []byte("master secret")
-var extendedMasterSecretLabel = []byte("extended master secret")
-var keyExpansionLabel = []byte("key expansion")
-var clientFinishedLabel = []byte("client finished")
-var serverFinishedLabel = []byte("server finished")
+const masterSecretLabel = "master secret"
+const extendedMasterSecretLabel = "extended master secret"
+const keyExpansionLabel = "key expansion"
+const clientFinishedLabel = "client finished"
+const serverFinishedLabel = "server finished"
 
-func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secret, label, seed []byte), crypto.Hash) {
+func prfAndHashForVersion(version uint16, suite *cipherSuite) (prfFunc, crypto.Hash) {
 	switch version {
 	case VersionTLS10, VersionTLS11:
 		return prf10, crypto.Hash(0)
@@ -99,7 +101,7 @@ func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secr
 	}
 }
 
-func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
+func prfForVersion(version uint16, suite *cipherSuite) prfFunc {
 	prf, _ := prfAndHashForVersion(version, suite)
 	return prf
 }
@@ -111,17 +113,19 @@ func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecr
 	seed = append(seed, clientRandom...)
 	seed = append(seed, serverRandom...)
 
-	masterSecret := make([]byte, masterSecretLength)
-	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed)
-	return masterSecret
+	return prfForVersion(version, suite)(preMasterSecret, masterSecretLabel, seed, masterSecretLength)
 }
 
 // extMasterFromPreMasterSecret generates the extended master secret from the
 // pre-master secret. See RFC 7627.
 func extMasterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, transcript []byte) []byte {
-	masterSecret := make([]byte, masterSecretLength)
-	prfForVersion(version, suite)(masterSecret, preMasterSecret, extendedMasterSecretLabel, transcript)
-	return masterSecret
+	prf, hash := prfAndHashForVersion(version, suite)
+	if version == VersionTLS12 {
+		// Use the FIPS 140-3 module only for TLS 1.2 with EMS, which is the
+		// only TLS 1.0-1.2 approved mode per IG D.Q.
+		return tls12.MasterSecret(hash.New, preMasterSecret, transcript)
+	}
+	return prf(preMasterSecret, extendedMasterSecretLabel, transcript, masterSecretLength)
 }
 
 // keysFromMasterSecret generates the connection keys from the master
@@ -133,8 +137,7 @@ func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clie
 	seed = append(seed, clientRandom...)
 
 	n := 2*macLen + 2*keyLen + 2*ivLen
-	keyMaterial := make([]byte, n)
-	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed)
+	keyMaterial := prfForVersion(version, suite)(masterSecret, keyExpansionLabel, seed, n)
 	clientMAC = keyMaterial[:macLen]
 	keyMaterial = keyMaterial[macLen:]
 	serverMAC = keyMaterial[:macLen]
@@ -177,7 +180,7 @@ type finishedHash struct {
 	buffer []byte
 
 	version uint16
-	prf     func(result, secret, label, seed []byte)
+	prf     prfFunc
 }
 
 func (h *finishedHash) Write(msg []byte) (n int, err error) {
@@ -209,17 +212,13 @@ func (h finishedHash) Sum() []byte {
 // clientSum returns the contents of the verify_data member of a client's
 // Finished message.
 func (h finishedHash) clientSum(masterSecret []byte) []byte {
-	out := make([]byte, finishedVerifyLength)
-	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
-	return out
+	return h.prf(masterSecret, clientFinishedLabel, h.Sum(), finishedVerifyLength)
 }
 
 // serverSum returns the contents of the verify_data member of a server's
 // Finished message.
 func (h finishedHash) serverSum(masterSecret []byte) []byte {
-	out := make([]byte, finishedVerifyLength)
-	h.prf(out, masterSecret, serverFinishedLabel, h.Sum())
-	return out
+	return h.prf(masterSecret, serverFinishedLabel, h.Sum(), finishedVerifyLength)
 }
 
 // hashForClientCertificate returns the handshake messages so far, pre-hashed if
@@ -292,8 +291,6 @@ func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clien
 			seed = append(seed, context...)
 		}
 
-		keyMaterial := make([]byte, length)
-		prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
-		return keyMaterial, nil
+		return prfForVersion(version, suite)(masterSecret, label, seed, length), nil
 	}
 }

src/go/build/deps_test.go

@@ -462,6 +462,7 @@ var depsRules = `
 	< crypto/internal/fips/hmac
 	< crypto/internal/fips/check
 	< crypto/internal/fips/hkdf
+	< crypto/internal/fips/tls12
 	< crypto/internal/fips/tls13
 	< FIPS;