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crypto/tls: support X25519.
X25519 (RFC 7748) is now commonly used for key agreement in TLS connections, as specified in https://tools.ietf.org/html/draft-ietf-tls-curve25519-01. This change adds support for that in crypto/tls, but does not enabled it by default so that there's less test noise. A future change will enable it by default and will update all the test data at the same time. Change-Id: I91802ecd776d73aae5c65bcb653d12e23c413ed4 Reviewed-on: https://go-review.googlesource.com/30824 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Adam Langley
parent
ef11ee4062
commit
6bcda018f7
6 changed files with 302 additions and 44 deletions
156
key_agreement.go
156
key_agreement.go
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@ -16,6 +16,8 @@ import (
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"errors"
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"io"
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"math/big"
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"golang_org/x/crypto/curve25519"
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)
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var errClientKeyExchange = errors.New("tls: invalid ClientKeyExchange message")
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@ -177,52 +179,71 @@ type ecdheKeyAgreement struct {
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version uint16
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sigType uint8
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privateKey []byte
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curve elliptic.Curve
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x, y *big.Int
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curveid CurveID
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// publicKey is used to store the peer's public value when X25519 is
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// being used.
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publicKey []byte
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// x and y are used to store the peer's public value when one of the
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// NIST curves is being used.
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x, y *big.Int
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}
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func (ka *ecdheKeyAgreement) generateServerKeyExchange(config *Config, cert *Certificate, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, error) {
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var curveid CurveID
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preferredCurves := config.curvePreferences()
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NextCandidate:
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for _, candidate := range preferredCurves {
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for _, c := range clientHello.supportedCurves {
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if candidate == c {
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curveid = c
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ka.curveid = c
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break NextCandidate
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}
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}
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}
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if curveid == 0 {
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if ka.curveid == 0 {
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return nil, errors.New("tls: no supported elliptic curves offered")
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}
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var ok bool
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if ka.curve, ok = curveForCurveID(curveid); !ok {
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return nil, errors.New("tls: preferredCurves includes unsupported curve")
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}
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var ecdhePublic []byte
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var x, y *big.Int
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var err error
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ka.privateKey, x, y, err = elliptic.GenerateKey(ka.curve, config.rand())
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if err != nil {
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return nil, err
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if ka.curveid == X25519 {
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var scalar, public [32]byte
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if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil {
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return nil, err
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}
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curve25519.ScalarBaseMult(&public, &scalar)
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ka.privateKey = scalar[:]
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ecdhePublic = public[:]
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} else {
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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return nil, errors.New("tls: preferredCurves includes unsupported curve")
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}
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var x, y *big.Int
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var err error
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ka.privateKey, x, y, err = elliptic.GenerateKey(curve, config.rand())
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if err != nil {
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return nil, err
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}
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ecdhePublic = elliptic.Marshal(curve, x, y)
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}
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ecdhePublic := elliptic.Marshal(ka.curve, x, y)
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// http://tools.ietf.org/html/rfc4492#section-5.4
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serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
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serverECDHParams[0] = 3 // named curve
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serverECDHParams[1] = byte(curveid >> 8)
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serverECDHParams[2] = byte(curveid)
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serverECDHParams[1] = byte(ka.curveid >> 8)
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serverECDHParams[2] = byte(ka.curveid)
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serverECDHParams[3] = byte(len(ecdhePublic))
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copy(serverECDHParams[4:], ecdhePublic)
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sigAndHash := signatureAndHash{signature: ka.sigType}
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if ka.version >= VersionTLS12 {
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var err error
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if sigAndHash.hash, err = pickTLS12HashForSignature(ka.sigType, clientHello.signatureAndHashes); err != nil {
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return nil, err
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}
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@ -281,15 +302,32 @@ func (ka *ecdheKeyAgreement) processClientKeyExchange(config *Config, cert *Cert
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if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
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return nil, errClientKeyExchange
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}
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x, y := elliptic.Unmarshal(ka.curve, ckx.ciphertext[1:])
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if ka.curveid == X25519 {
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if len(ckx.ciphertext) != 1+32 {
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return nil, errClientKeyExchange
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}
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var theirPublic, sharedKey, scalar [32]byte
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copy(theirPublic[:], ckx.ciphertext[1:])
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copy(scalar[:], ka.privateKey)
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curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic)
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return sharedKey[:], nil
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}
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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panic("internal error")
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}
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x, y := elliptic.Unmarshal(curve, ckx.ciphertext[1:])
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if x == nil {
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return nil, errClientKeyExchange
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}
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if !ka.curve.IsOnCurve(x, y) {
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if !curve.IsOnCurve(x, y) {
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return nil, errClientKeyExchange
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}
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x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
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preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
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x, _ = curve.ScalarMult(x, y, ka.privateKey)
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preMasterSecret := make([]byte, (curve.Params().BitSize+7)>>3)
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xBytes := x.Bytes()
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copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
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@ -303,31 +341,40 @@ func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHell
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if skx.key[0] != 3 { // named curve
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return errors.New("tls: server selected unsupported curve")
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}
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curveid := CurveID(skx.key[1])<<8 | CurveID(skx.key[2])
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var ok bool
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if ka.curve, ok = curveForCurveID(curveid); !ok {
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return errors.New("tls: server selected unsupported curve")
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}
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ka.curveid = CurveID(skx.key[1])<<8 | CurveID(skx.key[2])
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publicLen := int(skx.key[3])
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if publicLen+4 > len(skx.key) {
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return errServerKeyExchange
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}
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ka.x, ka.y = elliptic.Unmarshal(ka.curve, skx.key[4:4+publicLen])
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if ka.x == nil {
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return errServerKeyExchange
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}
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if !ka.curve.IsOnCurve(ka.x, ka.y) {
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return errServerKeyExchange
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}
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serverECDHParams := skx.key[:4+publicLen]
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publicKey := serverECDHParams[4:]
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sig := skx.key[4+publicLen:]
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if len(sig) < 2 {
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return errServerKeyExchange
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}
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if ka.curveid == X25519 {
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if len(publicKey) != 32 {
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return errors.New("tls: bad X25519 public value")
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}
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ka.publicKey = publicKey
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} else {
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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return errors.New("tls: server selected unsupported curve")
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}
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ka.x, ka.y = elliptic.Unmarshal(curve, publicKey)
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if ka.x == nil {
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return errServerKeyExchange
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}
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if !curve.IsOnCurve(ka.x, ka.y) {
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return errServerKeyExchange
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}
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}
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sigAndHash := signatureAndHash{signature: ka.sigType}
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if ka.version >= VersionTLS12 {
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// handle SignatureAndHashAlgorithm
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@ -382,19 +429,40 @@ func (ka *ecdheKeyAgreement) processServerKeyExchange(config *Config, clientHell
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}
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func (ka *ecdheKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, error) {
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if ka.curve == nil {
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if ka.curveid == 0 {
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return nil, nil, errors.New("tls: missing ServerKeyExchange message")
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}
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priv, mx, my, err := elliptic.GenerateKey(ka.curve, config.rand())
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if err != nil {
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return nil, nil, err
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}
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x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
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preMasterSecret := make([]byte, (ka.curve.Params().BitSize+7)>>3)
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xBytes := x.Bytes()
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copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
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serialized := elliptic.Marshal(ka.curve, mx, my)
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var serialized, preMasterSecret []byte
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if ka.curveid == X25519 {
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var ourPublic, theirPublic, sharedKey, scalar [32]byte
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if _, err := io.ReadFull(config.rand(), scalar[:]); err != nil {
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return nil, nil, err
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}
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copy(theirPublic[:], ka.publicKey)
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curve25519.ScalarBaseMult(&ourPublic, &scalar)
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curve25519.ScalarMult(&sharedKey, &scalar, &theirPublic)
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serialized = ourPublic[:]
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preMasterSecret = sharedKey[:]
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} else {
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curve, ok := curveForCurveID(ka.curveid)
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if !ok {
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panic("internal error")
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}
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priv, mx, my, err := elliptic.GenerateKey(curve, config.rand())
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if err != nil {
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return nil, nil, err
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}
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x, _ := curve.ScalarMult(ka.x, ka.y, priv)
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preMasterSecret = make([]byte, (curve.Params().BitSize+7)>>3)
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xBytes := x.Bytes()
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copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
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serialized = elliptic.Marshal(curve, mx, my)
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}
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ckx := new(clientKeyExchangeMsg)
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ckx.ciphertext = make([]byte, 1+len(serialized))
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