1 files changed, 413 insertions, 0 deletions
diff --git a/src/crypto/tls/key_agreement.go b/src/crypto/tls/key_agreement.go
new file mode 100644
index 000000000..0974fc6e0
--- /dev/null
+++ b/src/crypto/tls/key_agreement.go
@@ -0,0 +1,413 @@
+// Copyright 2010 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/ecdsa"
+	"crypto/elliptic"
+	"crypto/md5"
+	"crypto/rsa"
+	"crypto/sha1"
+	"crypto/sha256"
+	"crypto/x509"
+	"encoding/asn1"
+	"errors"
+	"io"
+	"math/big"
+)
+
+var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message")
+var errServerKeyExchange = errors.New("tls: invalid ServerKeyExchange message")
+
+// rsaKeyAgreement implements the standard TLS key agreement where the client
+// encrypts the pre-master secret to the server's public key.
+type rsaKeyAgreement struct{}
+
+func (ka rsaKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
+	return nil, nil
+}
+
+func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
+	preMasterSecret := make([]byte, 48)
+	_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
+	if err != nil {
+		return nil, err
+	}
+
+	if len(ckx.ciphertext) < 2 {
+		return nil, errClientKeyExchange
+	}
+
+	ciphertext := ckx.ciphertext
+	if version != VersionSSL30 {
+		ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1])
+		if ciphertextLen != len(ckx.ciphertext)-2 {
+			return nil, errClientKeyExchange
+		}
+		ciphertext = ckx.ciphertext[2:]
+	}
+
+	err = rsa.DecryptPKCS1v15SessionKey(config.rand(), cert.PrivateKey.(*rsa.PrivateKey), ciphertext, preMasterSecret)
+	if err != nil {
+		return nil, err
+	}
+	// We don't check the version number in the premaster secret.  For one,
+	// by checking it, we would leak information about the validity of the
+	// encrypted pre-master secret. Secondly, it provides only a small
+	// benefit against a downgrade attack and some implementations send the
+	// wrong version anyway. See the discussion at the end of section
+	// 7.4.7.1 of RFC 4346.
+	return preMasterSecret, nil
+}
+
+func (ka rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
+	return errors.New("tls: unexpected ServerKeyExchange")
+}
+
+func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
+	preMasterSecret := make([]byte, 48)
+	preMasterSecret[0] = byte(clientHello.vers >> 8)
+	preMasterSecret[1] = byte(clientHello.vers)
+	_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
+	if err != nil {
+		return nil, nil, err
+	}
+
+	encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret)
+	if err != nil {
+		return nil, nil, err
+	}
+	ckx := new(clientKeyExchangeMsg)
+	ckx.ciphertext = make([]byte, len(encrypted)+2)
+	ckx.ciphertext[0] = byte(len(encrypted) >> 8)
+	ckx.ciphertext[1] = byte(len(encrypted))
+	copy(ckx.ciphertext[2:], encrypted)
+	return preMasterSecret, ckx, nil
+}
+
+// sha1Hash calculates a SHA1 hash over the given byte slices.
+func sha1Hash(slices [][]byte) []byte {
+	hsha1 := sha1.New()
+	for _, slice := range slices {
+		hsha1.Write(slice)
+	}
+	return hsha1.Sum(nil)
+}
+
+// md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the
+// concatenation of an MD5 and SHA1 hash.
+func md5SHA1Hash(slices [][]byte) []byte {
+	md5sha1 := make([]byte, md5.Size+sha1.Size)
+	hmd5 := md5.New()
+	for _, slice := range slices {
+		hmd5.Write(slice)
+	}
+	copy(md5sha1, hmd5.Sum(nil))
+	copy(md5sha1[md5.Size:], sha1Hash(slices))
+	return md5sha1
+}
+
+// sha256Hash implements TLS 1.2's hash function.
+func sha256Hash(slices [][]byte) []byte {
+	h := sha256.New()
+	for _, slice := range slices {
+		h.Write(slice)
+	}
+	return h.Sum(nil)
+}
+
+// hashForServerKeyExchange hashes the given slices and returns their digest
+// and the identifier of the hash function used. The hashFunc argument is only
+// used for >= TLS 1.2 and precisely identifies the hash function to use.
+func hashForServerKeyExchange(sigType, hashFunc uint8, version uint16, slices ...[]byte) ([]byte, crypto.Hash, error) {
+	if version >= VersionTLS12 {
+		switch hashFunc {
+		case hashSHA256:
+			return sha256Hash(slices), crypto.SHA256, nil
+		case hashSHA1:
+			return sha1Hash(slices), crypto.SHA1, nil
+		default:
+			return nil, crypto.Hash(0), errors.New("tls: unknown hash function used by peer")
+		}
+	}
+	if sigType == signatureECDSA {
+		return sha1Hash(slices), crypto.SHA1, nil
+	}
+	return md5SHA1Hash(slices), crypto.MD5SHA1, nil
+}
+
+// pickTLS12HashForSignature returns a TLS 1.2 hash identifier for signing a
+// ServerKeyExchange given the signature type being used and the client's
+// advertised list of supported signature and hash combinations.
+func pickTLS12HashForSignature(sigType uint8, clientSignatureAndHashes []signatureAndHash) (uint8, error) {
+	if len(clientSignatureAndHashes) == 0 {
+		// If the client didn't specify any signature_algorithms
+		// extension then we can assume that it supports SHA1. See
+		// http://tools.ietf.org/html/rfc5246#section-7.4.1.4.1
+		return hashSHA1, nil
+	}
+
+	for _, sigAndHash := range clientSignatureAndHashes {
+		if sigAndHash.signature != sigType {
+			continue
+		}
+		switch sigAndHash.hash {
+		case hashSHA1, hashSHA256:
+			return sigAndHash.hash, nil
+		}
+	}
+
+	return 0, errors.New("tls: client doesn't support any common hash functions")
+}
+
+func curveForCurveID(id CurveID) (elliptic.Curve, bool) {
+	switch id {
+	case CurveP256:
+		return elliptic.P256(), true
+	case CurveP384:
+		return elliptic.P384(), true
+	case CurveP521:
+		return elliptic.P521(), true
+	default:
+		return nil, false
+	}
+
+}
+
+// ecdheRSAKeyAgreement implements a TLS key agreement where the server
+// generates a ephemeral EC public/private key pair and signs it. The
+// pre-master secret is then calculated using ECDH. The signature may
+// either be ECDSA or RSA.
+type ecdheKeyAgreement struct {
+	version    uint16
+	sigType    uint8
+	privateKey []byte
+	curve      elliptic.Curve
+	x, y       *big.Int
+}
+
+func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
+	var curveid CurveID
+	preferredCurves := config.curvePreferences()
+
+NextCandidate:
+	for _, candidate := range preferredCurves {
+		for _, c := range clientHello.supportedCurves {
+			if candidate == c {
+				curveid = c
+				break NextCandidate
+			}
+		}
+	}
+
+	if curveid == 0 {
+		return nil, errors.New("tls: no supported elliptic curves offered")
+	}
+
+	var ok bool
+	if ka.curve, ok = curveForCurveID(curveid); !ok {
+		return nil, errors.New("tls: preferredCurves includes unsupported curve")
+	}
+
+	var x, y *big.Int
+	var err error
+	ka.privateKey, x, y, err = elliptic.GenerateKey(ka.curve, config.rand())
+	if err != nil {
+		return nil, err
+	}
+	ecdhePublic := elliptic.Marshal(ka.curve, x, y)
+
+	// http://tools.ietf.org/html/rfc4492#section-5.4
+	serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
+	serverECDHParams[0] = 3 // named curve
+	serverECDHParams[1] = byte(curveid >> 8)
+	serverECDHParams[2] = byte(curveid)
+	serverECDHParams[3] = byte(len(ecdhePublic))
+	copy(serverECDHParams[4:], ecdhePublic)
+
+	var tls12HashId uint8
+	if ka.version >= VersionTLS12 {
+		if tls12HashId, err = pickTLS12HashForSignature(ka.sigType, clientHello.signatureAndHashes); err != nil {
+			return nil, err
+		}
+	}
+
+	digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, hello.random, serverECDHParams)
+	if err != nil {
+		return nil, err
+	}
+	var sig []byte
+	switch ka.sigType {
+	case signatureECDSA:
+		privKey, ok := cert.PrivateKey.(*ecdsa.PrivateKey)
+		if !ok {
+			return nil, errors.New("ECDHE ECDSA requires an ECDSA server private key")
+		}
+		r, s, err := ecdsa.Sign(config.rand(), privKey, digest)
+		if err != nil {
+			return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
+		}
+		sig, err = asn1.Marshal(ecdsaSignature{r, s})
+	case signatureRSA:
+		privKey, ok := cert.PrivateKey.(*rsa.PrivateKey)
+		if !ok {
+			return nil, errors.New("ECDHE RSA requires a RSA server private key")
+		}
+		sig, err = rsa.SignPKCS1v15(config.rand(), privKey, hashFunc, digest)
+		if err != nil {
+			return nil, errors.New("failed to sign ECDHE parameters: " + err.Error())
+		}
+	default:
+		return nil, errors.New("unknown ECDHE signature algorithm")
+	}
+
+	skx := new(serverKeyExchangeMsg)
+	sigAndHashLen := 0
+	if ka.version >= VersionTLS12 {
+		sigAndHashLen = 2
+	}
+	skx.key = make([]byte, len(serverECDHParams)+sigAndHashLen+2+len(sig))
+	copy(skx.key, serverECDHParams)
+	k := skx.key[len(serverECDHParams):]
+	if ka.version >= VersionTLS12 {
+		k[0] = tls12HashId
+		k[1] = ka.sigType
+		k = k[2:]
+	}
+	k[0] = byte(len(sig) >> 8)
+	k[1] = byte(len(sig))
+	copy(k[2:], sig)
+
+	return skx, nil
+}
+
+func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Certificate, ckx *clientKeyExchangeMsg, version uint16) ([]byte, error) {
+	if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
+		return nil, errClientKeyExchange
+	}
+	x, y := elliptic.Unmarshal(ka.curve, ckx.ciphertext[1:])
+	if x == nil {
+		return nil, errClientKeyExchange
+	}
+	if !ka.curve.IsOnCurve(x, y) {
+		return nil, errClientKeyExchange
+	}
+	x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
+	preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
+	xBytes := x.Bytes()
+	copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
+
+	return preMasterSecret, nil
+}
+
+func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) error {
+	if len(skx.key) < 4 {
+		return errServerKeyExchange
+	}
+	if skx.key[0] != 3 { // named curve
+		return errors.New("tls: server selected unsupported curve")
+	}
+	curveid := CurveID(skx.key[1])<<8 | CurveID(skx.key[2])
+
+	var ok bool
+	if ka.curve, ok = curveForCurveID(curveid); !ok {
+		return errors.New("tls: server selected unsupported curve")
+	}
+
+	publicLen := int(skx.key[3])
+	if publicLen+4 > len(skx.key) {
+		return errServerKeyExchange
+	}
+	ka.x, ka.y = elliptic.Unmarshal(ka.curve, skx.key[4:4+publicLen])
+	if ka.x == nil {
+		return errServerKeyExchange
+	}
+	if !ka.curve.IsOnCurve(ka.x, ka.y) {
+		return errServerKeyExchange
+	}
+	serverECDHParams := skx.key[:4+publicLen]
+
+	sig := skx.key[4+publicLen:]
+	if len(sig) < 2 {
+		return errServerKeyExchange
+	}
+
+	var tls12HashId uint8
+	if ka.version >= VersionTLS12 {
+		// handle SignatureAndHashAlgorithm
+		var sigAndHash []uint8
+		sigAndHash, sig = sig[:2], sig[2:]
+		if sigAndHash[1] != ka.sigType {
+			return errServerKeyExchange
+		}
+		tls12HashId = sigAndHash[0]
+		if len(sig) < 2 {
+			return errServerKeyExchange
+		}
+	}
+	sigLen := int(sig[0])<<8 | int(sig[1])
+	if sigLen+2 != len(sig) {
+		return errServerKeyExchange
+	}
+	sig = sig[2:]
+
+	digest, hashFunc, err := hashForServerKeyExchange(ka.sigType, tls12HashId, ka.version, clientHello.random, serverHello.random, serverECDHParams)
+	if err != nil {
+		return err
+	}
+	switch ka.sigType {
+	case signatureECDSA:
+		pubKey, ok := cert.PublicKey.(*ecdsa.PublicKey)
+		if !ok {
+			return errors.New("ECDHE ECDSA requires a ECDSA server public key")
+		}
+		ecdsaSig := new(ecdsaSignature)
+		if _, err := asn1.Unmarshal(sig, ecdsaSig); err != nil {
+			return err
+		}
+		if ecdsaSig.R.Sign() <= 0 || ecdsaSig.S.Sign() <= 0 {
+			return errors.New("ECDSA signature contained zero or negative values")
+		}
+		if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) {
+			return errors.New("ECDSA verification failure")
+		}
+	case signatureRSA:
+		pubKey, ok := cert.PublicKey.(*rsa.PublicKey)
+		if !ok {
+			return errors.New("ECDHE RSA requires a RSA server public key")
+		}
+		if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil {
+			return err
+		}
+	default:
+		return errors.New("unknown ECDHE signature algorithm")
+	}
+
+	return nil
+}
+
+func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
+	if ka.curve == nil {
+		return nil, nil, errors.New("missing ServerKeyExchange message")
+	}
+	priv, mx, my, err := elliptic.GenerateKey(ka.curve, config.rand())
+	if err != nil {
+		return nil, nil, err
+	}
+	x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
+	preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
+	xBytes := x.Bytes()
+	copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
+
+	serialized := elliptic.Marshal(ka.curve, mx, my)
+
+	ckx := new(clientKeyExchangeMsg)
+	ckx.ciphertext = make([]byte, 1+len(serialized))
+	ckx.ciphertext[0] = byte(len(serialized))
+	copy(ckx.ciphertext[1:], serialized)
+
+	return preMasterSecret, ckx, nil
+}