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// Copyright 2017 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/rsa"
"encoding/asn1"
"errors"
"fmt"
"hash"
"io"
)
// pickSignatureAlgorithm selects a signature algorithm that is compatible with
// the given public key and the list of algorithms from the peer and this side.
// The lists of signature algorithms (peerSigAlgs and ourSigAlgs) are ignored
// for tlsVersion < VersionTLS12.
//
// The returned SignatureScheme codepoint is only meaningful for TLS 1.2,
// previous TLS versions have a fixed hash function.
func pickSignatureAlgorithm(pubkey crypto.PublicKey, peerSigAlgs, ourSigAlgs []SignatureScheme, tlsVersion uint16) (sigAlg SignatureScheme, sigType uint8, hashFunc crypto.Hash, err error) {
if tlsVersion < VersionTLS12 || len(peerSigAlgs) == 0 {
// For TLS 1.1 and before, the signature algorithm could not be
// negotiated and the hash is fixed based on the signature type. For TLS
// 1.2, if the client didn't send signature_algorithms extension then we
// can assume that it supports SHA1. See RFC 5246, Section 7.4.1.4.1.
switch pubkey.(type) {
case *rsa.PublicKey:
if tlsVersion < VersionTLS12 {
return 0, signaturePKCS1v15, crypto.MD5SHA1, nil
} else {
return PKCS1WithSHA1, signaturePKCS1v15, crypto.SHA1, nil
}
case *ecdsa.PublicKey:
return ECDSAWithSHA1, signatureECDSA, crypto.SHA1, nil
default:
return 0, 0, 0, fmt.Errorf("tls: unsupported public key: %T", pubkey)
}
}
for _, sigAlg := range peerSigAlgs {
if !isSupportedSignatureAlgorithm(sigAlg, ourSigAlgs) {
continue
}
hashAlg, err := hashFromSignatureScheme(sigAlg)
if err != nil {
panic("tls: supported signature algorithm has an unknown hash function")
}
sigType := signatureFromSignatureScheme(sigAlg)
switch pubkey.(type) {
case *rsa.PublicKey:
if sigType == signaturePKCS1v15 || sigType == signatureRSAPSS {
return sigAlg, sigType, hashAlg, nil
}
case *ecdsa.PublicKey:
if sigType == signatureECDSA {
return sigAlg, sigType, hashAlg, nil
}
default:
return 0, 0, 0, fmt.Errorf("tls: unsupported public key: %T", pubkey)
}
}
return 0, 0, 0, errors.New("tls: peer doesn't support any common signature algorithms")
}
// verifyHandshakeSignature verifies a signature against pre-hashed handshake
// contents.
func verifyHandshakeSignature(sigType uint8, pubkey crypto.PublicKey, hashFunc crypto.Hash, digest, sig []byte) error {
switch sigType {
case signatureECDSA:
pubKey, ok := pubkey.(*ecdsa.PublicKey)
if !ok {
return errors.New("tls: ECDSA signing requires a ECDSA 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("tls: ECDSA signature contained zero or negative values")
}
if !ecdsa.Verify(pubKey, digest, ecdsaSig.R, ecdsaSig.S) {
return errors.New("tls: ECDSA verification failure")
}
case signaturePKCS1v15:
pubKey, ok := pubkey.(*rsa.PublicKey)
if !ok {
return errors.New("tls: RSA signing requires a RSA public key")
}
if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, digest, sig); err != nil {
return err
}
case signatureRSAPSS:
pubKey, ok := pubkey.(*rsa.PublicKey)
if !ok {
return errors.New("tls: RSA signing requires a RSA public key")
}
signOpts := &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash}
if err := rsa.VerifyPSS(pubKey, hashFunc, digest, sig, signOpts); err != nil {
return err
}
default:
return errors.New("tls: unknown signature algorithm")
}
return nil
}
const (
serverSignatureContext = "TLS 1.3, server CertificateVerify\x00"
clientSignatureContext = "TLS 1.3, client CertificateVerify\x00"
)
var signaturePadding = []byte{
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
}
// writeSignedMessage writes the content to be signed by certificate keys in TLS
// 1.3 to sigHash. See RFC 8446, Section 4.4.3.
func writeSignedMessage(sigHash io.Writer, context string, transcript hash.Hash) {
sigHash.Write(signaturePadding)
io.WriteString(sigHash, context)
sigHash.Write(transcript.Sum(nil))
}
// signatureSchemesForCertificate returns the list of supported SignatureSchemes
// for a given certificate, based on the public key and the protocol version. It
// does not support the crypto.Decrypter interface, so shouldn't be used on the
// server side in TLS 1.2 and earlier.
func signatureSchemesForCertificate(version uint16, cert *Certificate) []SignatureScheme {
priv, ok := cert.PrivateKey.(crypto.Signer)
if !ok {
return nil
}
switch pub := priv.Public().(type) {
case *ecdsa.PublicKey:
if version != VersionTLS13 {
// In TLS 1.2 and earlier, ECDSA algorithms are not
// constrained to a single curve.
return []SignatureScheme{
ECDSAWithP256AndSHA256,
ECDSAWithP384AndSHA384,
ECDSAWithP521AndSHA512,
ECDSAWithSHA1,
}
}
switch pub.Curve {
case elliptic.P256():
return []SignatureScheme{ECDSAWithP256AndSHA256}
case elliptic.P384():
return []SignatureScheme{ECDSAWithP384AndSHA384}
case elliptic.P521():
return []SignatureScheme{ECDSAWithP521AndSHA512}
default:
return nil
}
case *rsa.PublicKey:
if version != VersionTLS13 {
return []SignatureScheme{
PSSWithSHA256,
PSSWithSHA384,
PSSWithSHA512,
PKCS1WithSHA256,
PKCS1WithSHA384,
PKCS1WithSHA512,
PKCS1WithSHA1,
}
}
// RSA keys with RSA-PSS OID are not supported by crypto/x509.
return []SignatureScheme{
PSSWithSHA256,
PSSWithSHA384,
PSSWithSHA512,
}
default:
return nil
}
}
// unsupportedCertificateError returns a helpful error for certificates with
// an unsupported private key.
func unsupportedCertificateError(cert *Certificate) error {
switch cert.PrivateKey.(type) {
case rsa.PrivateKey, ecdsa.PrivateKey:
return fmt.Errorf("tls: unsupported certificate: private key is %T, expected *%T",
cert.PrivateKey, cert.PrivateKey)
}
signer, ok := cert.PrivateKey.(crypto.Signer)
if !ok {
return fmt.Errorf("tls: certificate private key (%T) does not implement crypto.Signer",
cert.PrivateKey)
}
switch pub := signer.Public().(type) {
case *ecdsa.PublicKey:
switch pub.Curve {
case elliptic.P256():
case elliptic.P384():
case elliptic.P521():
default:
return fmt.Errorf("tls: unsupported certificate curve (%s)", pub.Curve.Params().Name)
}
case *rsa.PublicKey:
default:
return fmt.Errorf("tls: unsupported certificate key (%T)", pub)
}
return fmt.Errorf("tls: internal error: unsupported key (%T)", cert.PrivateKey)
}
