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Source file src/crypto/tls/prf.go

Documentation: crypto/tls

  // Copyright 2009 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 tls
  
  import (
  	"crypto"
  	"crypto/hmac"
  	"crypto/md5"
  	"crypto/sha1"
  	"crypto/sha256"
  	"crypto/sha512"
  	"errors"
  	"fmt"
  	"hash"
  )
  
  // 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]
  	s2 = secret[len(secret)/2:]
  	return
  }
  
  // pHash implements the P_hash function, as defined in RFC 4346, section 5.
  func pHash(result, secret, seed []byte, hash func() hash.Hash) {
  	h := hmac.New(hash, secret)
  	h.Write(seed)
  	a := h.Sum(nil)
  
  	j := 0
  	for j < len(result) {
  		h.Reset()
  		h.Write(a)
  		h.Write(seed)
  		b := h.Sum(nil)
  		copy(result[j:], b)
  		j += len(b)
  
  		h.Reset()
  		h.Write(a)
  		a = h.Sum(nil)
  	}
  }
  
  // prf10 implements the TLS 1.0 pseudo-random function, as defined in RFC 2246, section 5.
  func prf10(result, secret, label, seed []byte) {
  	hashSHA1 := sha1.New
  	hashMD5 := md5.New
  
  	labelAndSeed := make([]byte, len(label)+len(seed))
  	copy(labelAndSeed, label)
  	copy(labelAndSeed[len(label):], seed)
  
  	s1, s2 := splitPreMasterSecret(secret)
  	pHash(result, s1, labelAndSeed, hashMD5)
  	result2 := make([]byte, len(result))
  	pHash(result2, s2, labelAndSeed, hashSHA1)
  
  	for i, b := range result2 {
  		result[i] ^= b
  	}
  }
  
  // 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)
  	}
  }
  
  // prf30 implements the SSL 3.0 pseudo-random function, as defined in
  // www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt section 6.
  func prf30(result, secret, label, seed []byte) {
  	hashSHA1 := sha1.New()
  	hashMD5 := md5.New()
  
  	done := 0
  	i := 0
  	// RFC 5246 section 6.3 says that the largest PRF output needed is 128
  	// bytes. Since no more ciphersuites will be added to SSLv3, this will
  	// remain true. Each iteration gives us 16 bytes so 10 iterations will
  	// be sufficient.
  	var b [11]byte
  	for done < len(result) {
  		for j := 0; j <= i; j++ {
  			b[j] = 'A' + byte(i)
  		}
  
  		hashSHA1.Reset()
  		hashSHA1.Write(b[:i+1])
  		hashSHA1.Write(secret)
  		hashSHA1.Write(seed)
  		digest := hashSHA1.Sum(nil)
  
  		hashMD5.Reset()
  		hashMD5.Write(secret)
  		hashMD5.Write(digest)
  
  		done += copy(result[done:], hashMD5.Sum(nil))
  		i++
  	}
  }
  
  const (
  	tlsRandomLength      = 32 // Length of a random nonce in TLS 1.1.
  	masterSecretLength   = 48 // Length of a master secret in TLS 1.1.
  	finishedVerifyLength = 12 // Length of verify_data in a Finished message.
  )
  
  var masterSecretLabel = []byte("master secret")
  var keyExpansionLabel = []byte("key expansion")
  var clientFinishedLabel = []byte("client finished")
  var serverFinishedLabel = []byte("server finished")
  
  func prfAndHashForVersion(version uint16, suite *cipherSuite) (func(result, secret, label, seed []byte), crypto.Hash) {
  	switch version {
  	case VersionSSL30:
  		return prf30, crypto.Hash(0)
  	case VersionTLS10, VersionTLS11:
  		return prf10, crypto.Hash(0)
  	case VersionTLS12:
  		if suite.flags&suiteSHA384 != 0 {
  			return prf12(sha512.New384), crypto.SHA384
  		}
  		return prf12(sha256.New), crypto.SHA256
  	default:
  		panic("unknown version")
  	}
  }
  
  func prfForVersion(version uint16, suite *cipherSuite) func(result, secret, label, seed []byte) {
  	prf, _ := prfAndHashForVersion(version, suite)
  	return prf
  }
  
  // masterFromPreMasterSecret generates the master secret from the pre-master
  // secret. See https://tools.ietf.org/html/rfc5246#section-8.1
  func masterFromPreMasterSecret(version uint16, suite *cipherSuite, preMasterSecret, clientRandom, serverRandom []byte) []byte {
  	seed := make([]byte, 0, len(clientRandom)+len(serverRandom))
  	seed = append(seed, clientRandom...)
  	seed = append(seed, serverRandom...)
  
  	masterSecret := make([]byte, masterSecretLength)
  	prfForVersion(version, suite)(masterSecret, preMasterSecret, masterSecretLabel, seed)
  	return masterSecret
  }
  
  // keysFromMasterSecret generates the connection keys from the master
  // secret, given the lengths of the MAC key, cipher key and IV, as defined in
  // RFC 2246, section 6.3.
  func keysFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte, macLen, keyLen, ivLen int) (clientMAC, serverMAC, clientKey, serverKey, clientIV, serverIV []byte) {
  	seed := make([]byte, 0, len(serverRandom)+len(clientRandom))
  	seed = append(seed, serverRandom...)
  	seed = append(seed, clientRandom...)
  
  	n := 2*macLen + 2*keyLen + 2*ivLen
  	keyMaterial := make([]byte, n)
  	prfForVersion(version, suite)(keyMaterial, masterSecret, keyExpansionLabel, seed)
  	clientMAC = keyMaterial[:macLen]
  	keyMaterial = keyMaterial[macLen:]
  	serverMAC = keyMaterial[:macLen]
  	keyMaterial = keyMaterial[macLen:]
  	clientKey = keyMaterial[:keyLen]
  	keyMaterial = keyMaterial[keyLen:]
  	serverKey = keyMaterial[:keyLen]
  	keyMaterial = keyMaterial[keyLen:]
  	clientIV = keyMaterial[:ivLen]
  	keyMaterial = keyMaterial[ivLen:]
  	serverIV = keyMaterial[:ivLen]
  	return
  }
  
  // lookupTLSHash looks up the corresponding crypto.Hash for a given
  // hash from a TLS SignatureScheme.
  func lookupTLSHash(signatureAlgorithm SignatureScheme) (crypto.Hash, error) {
  	switch signatureAlgorithm {
  	case PKCS1WithSHA1, ECDSAWithSHA1:
  		return crypto.SHA1, nil
  	case PKCS1WithSHA256, PSSWithSHA256, ECDSAWithP256AndSHA256:
  		return crypto.SHA256, nil
  	case PKCS1WithSHA384, PSSWithSHA384, ECDSAWithP384AndSHA384:
  		return crypto.SHA384, nil
  	case PKCS1WithSHA512, PSSWithSHA512, ECDSAWithP521AndSHA512:
  		return crypto.SHA512, nil
  	default:
  		return 0, fmt.Errorf("tls: unsupported signature algorithm: %#04x", signatureAlgorithm)
  	}
  }
  
  func newFinishedHash(version uint16, cipherSuite *cipherSuite) finishedHash {
  	var buffer []byte
  	if version == VersionSSL30 || version >= VersionTLS12 {
  		buffer = []byte{}
  	}
  
  	prf, hash := prfAndHashForVersion(version, cipherSuite)
  	if hash != 0 {
  		return finishedHash{hash.New(), hash.New(), nil, nil, buffer, version, prf}
  	}
  
  	return finishedHash{sha1.New(), sha1.New(), md5.New(), md5.New(), buffer, version, prf}
  }
  
  // A finishedHash calculates the hash of a set of handshake messages suitable
  // for including in a Finished message.
  type finishedHash struct {
  	client hash.Hash
  	server hash.Hash
  
  	// Prior to TLS 1.2, an additional MD5 hash is required.
  	clientMD5 hash.Hash
  	serverMD5 hash.Hash
  
  	// In TLS 1.2, a full buffer is sadly required.
  	buffer []byte
  
  	version uint16
  	prf     func(result, secret, label, seed []byte)
  }
  
  func (h *finishedHash) Write(msg []byte) (n int, err error) {
  	h.client.Write(msg)
  	h.server.Write(msg)
  
  	if h.version < VersionTLS12 {
  		h.clientMD5.Write(msg)
  		h.serverMD5.Write(msg)
  	}
  
  	if h.buffer != nil {
  		h.buffer = append(h.buffer, msg...)
  	}
  
  	return len(msg), nil
  }
  
  func (h finishedHash) Sum() []byte {
  	if h.version >= VersionTLS12 {
  		return h.client.Sum(nil)
  	}
  
  	out := make([]byte, 0, md5.Size+sha1.Size)
  	out = h.clientMD5.Sum(out)
  	return h.client.Sum(out)
  }
  
  // finishedSum30 calculates the contents of the verify_data member of a SSLv3
  // Finished message given the MD5 and SHA1 hashes of a set of handshake
  // messages.
  func finishedSum30(md5, sha1 hash.Hash, masterSecret []byte, magic []byte) []byte {
  	md5.Write(magic)
  	md5.Write(masterSecret)
  	md5.Write(ssl30Pad1[:])
  	md5Digest := md5.Sum(nil)
  
  	md5.Reset()
  	md5.Write(masterSecret)
  	md5.Write(ssl30Pad2[:])
  	md5.Write(md5Digest)
  	md5Digest = md5.Sum(nil)
  
  	sha1.Write(magic)
  	sha1.Write(masterSecret)
  	sha1.Write(ssl30Pad1[:40])
  	sha1Digest := sha1.Sum(nil)
  
  	sha1.Reset()
  	sha1.Write(masterSecret)
  	sha1.Write(ssl30Pad2[:40])
  	sha1.Write(sha1Digest)
  	sha1Digest = sha1.Sum(nil)
  
  	ret := make([]byte, len(md5Digest)+len(sha1Digest))
  	copy(ret, md5Digest)
  	copy(ret[len(md5Digest):], sha1Digest)
  	return ret
  }
  
  var ssl3ClientFinishedMagic = [4]byte{0x43, 0x4c, 0x4e, 0x54}
  var ssl3ServerFinishedMagic = [4]byte{0x53, 0x52, 0x56, 0x52}
  
  // clientSum returns the contents of the verify_data member of a client's
  // Finished message.
  func (h finishedHash) clientSum(masterSecret []byte) []byte {
  	if h.version == VersionSSL30 {
  		return finishedSum30(h.clientMD5, h.client, masterSecret, ssl3ClientFinishedMagic[:])
  	}
  
  	out := make([]byte, finishedVerifyLength)
  	h.prf(out, masterSecret, clientFinishedLabel, h.Sum())
  	return out
  }
  
  // serverSum returns the contents of the verify_data member of a server's
  // Finished message.
  func (h finishedHash) serverSum(masterSecret []byte) []byte {
  	if h.version == VersionSSL30 {
  		return finishedSum30(h.serverMD5, h.server, masterSecret, ssl3ServerFinishedMagic[:])
  	}
  
  	out := make([]byte, finishedVerifyLength)
  	h.prf(out, masterSecret, serverFinishedLabel, h.Sum())
  	return out
  }
  
  // hashForClientCertificate returns a digest over the handshake messages so far,
  // suitable for signing by a TLS client certificate.
  func (h finishedHash) hashForClientCertificate(sigType uint8, hashAlg crypto.Hash, masterSecret []byte) ([]byte, error) {
  	if (h.version == VersionSSL30 || h.version >= VersionTLS12) && h.buffer == nil {
  		panic("a handshake hash for a client-certificate was requested after discarding the handshake buffer")
  	}
  
  	if h.version == VersionSSL30 {
  		if sigType != signaturePKCS1v15 {
  			return nil, errors.New("tls: unsupported signature type for client certificate")
  		}
  
  		md5Hash := md5.New()
  		md5Hash.Write(h.buffer)
  		sha1Hash := sha1.New()
  		sha1Hash.Write(h.buffer)
  		return finishedSum30(md5Hash, sha1Hash, masterSecret, nil), nil
  	}
  	if h.version >= VersionTLS12 {
  		hash := hashAlg.New()
  		hash.Write(h.buffer)
  		return hash.Sum(nil), nil
  	}
  
  	if sigType == signatureECDSA {
  		return h.server.Sum(nil), nil
  	}
  
  	return h.Sum(), nil
  }
  
  // discardHandshakeBuffer is called when there is no more need to
  // buffer the entirety of the handshake messages.
  func (h *finishedHash) discardHandshakeBuffer() {
  	h.buffer = nil
  }
  
  // noExportedKeyingMaterial is used as a value of
  // ConnectionState.ekm when renegotation is enabled and thus
  // we wish to fail all key-material export requests.
  func noExportedKeyingMaterial(label string, context []byte, length int) ([]byte, error) {
  	return nil, errors.New("crypto/tls: ExportKeyingMaterial is unavailable when renegotiation is enabled")
  }
  
  // ekmFromMasterSecret generates exported keying material as defined in
  // https://tools.ietf.org/html/rfc5705.
  func ekmFromMasterSecret(version uint16, suite *cipherSuite, masterSecret, clientRandom, serverRandom []byte) func(string, []byte, int) ([]byte, error) {
  	return func(label string, context []byte, length int) ([]byte, error) {
  		switch label {
  		case "client finished", "server finished", "master secret", "key expansion":
  			// These values are reserved and may not be used.
  			return nil, fmt.Errorf("crypto/tls: reserved ExportKeyingMaterial label: %s", label)
  		}
  
  		seedLen := len(serverRandom) + len(clientRandom)
  		if context != nil {
  			seedLen += 2 + len(context)
  		}
  		seed := make([]byte, 0, seedLen)
  
  		seed = append(seed, clientRandom...)
  		seed = append(seed, serverRandom...)
  
  		if context != nil {
  			if len(context) >= 1<<16 {
  				return nil, fmt.Errorf("crypto/tls: ExportKeyingMaterial context too long")
  			}
  			seed = append(seed, byte(len(context)>>8), byte(len(context)))
  			seed = append(seed, context...)
  		}
  
  		keyMaterial := make([]byte, length)
  		prfForVersion(version, suite)(keyMaterial, masterSecret, []byte(label), seed)
  		return keyMaterial, nil
  	}
  }
  

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