// 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 (
"bytes"
"crypto"
"crypto/ecdsa"
"crypto/ed25519"
"crypto/elliptic"
"crypto/rsa"
"errors"
"fmt"
"hash"
"io"
"slices"
)
// verifyHandshakeSignature verifies a signature against pre-hashed
// (if required) handshake contents.
func verifyHandshakeSignature(sigType uint8, pubkey crypto.PublicKey, hashFunc crypto.Hash, signed, sig []byte) error {
switch sigType {
case signatureECDSA:
pubKey, ok := pubkey.(*ecdsa.PublicKey)
if !ok {
return fmt.Errorf("expected an ECDSA public key, got %T", pubkey)
}
if !ecdsa.VerifyASN1(pubKey, signed, sig) {
return errors.New("ECDSA verification failure")
}
case signatureEd25519:
pubKey, ok := pubkey.(ed25519.PublicKey)
if !ok {
return fmt.Errorf("expected an Ed25519 public key, got %T", pubkey)
}
if !ed25519.Verify(pubKey, signed, sig) {
return errors.New("Ed25519 verification failure")
}
case signaturePKCS1v15:
pubKey, ok := pubkey.(*rsa.PublicKey)
if !ok {
return fmt.Errorf("expected an RSA public key, got %T", pubkey)
}
if err := rsa.VerifyPKCS1v15(pubKey, hashFunc, signed, sig); err != nil {
return err
}
case signatureRSAPSS:
pubKey, ok := pubkey.(*rsa.PublicKey)
if !ok {
return fmt.Errorf("expected an RSA public key, got %T", pubkey)
}
signOpts := &rsa.PSSOptions{SaltLength: rsa.PSSSaltLengthEqualsHash}
if err := rsa.VerifyPSS(pubKey, hashFunc, signed, sig, signOpts); err != nil {
return err
}
default:
return errors.New("internal error: unknown signature type")
}
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,
}
// signedMessage returns the pre-hashed (if necessary) message to be signed by
// certificate keys in TLS 1.3. See RFC 8446, Section 4.4.3.
func signedMessage(sigHash crypto.Hash, context string, transcript hash.Hash) []byte {
if sigHash == directSigning {
b := &bytes.Buffer{}
b.Write(signaturePadding)
io.WriteString(b, context)
b.Write(transcript.Sum(nil))
return b.Bytes()
}
h := sigHash.New()
h.Write(signaturePadding)
io.WriteString(h, context)
h.Write(transcript.Sum(nil))
return h.Sum(nil)
}
// typeAndHashFromSignatureScheme returns the corresponding signature type and
// crypto.Hash for a given TLS SignatureScheme.
func typeAndHashFromSignatureScheme(signatureAlgorithm SignatureScheme) (sigType uint8, hash crypto.Hash, err error) {
switch signatureAlgorithm {
case PKCS1WithSHA1, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512:
sigType = signaturePKCS1v15
case PSSWithSHA256, PSSWithSHA384, PSSWithSHA512:
sigType = signatureRSAPSS
case ECDSAWithSHA1, ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512:
sigType = signatureECDSA
case Ed25519:
sigType = signatureEd25519
default:
return 0, 0, fmt.Errorf("unsupported signature algorithm: %v", signatureAlgorithm)
}
switch signatureAlgorithm {
case PKCS1WithSHA1, ECDSAWithSHA1:
hash = crypto.SHA1
case PKCS1WithSHA256, PSSWithSHA256, ECDSAWithP256AndSHA256:
hash = crypto.SHA256
case PKCS1WithSHA384, PSSWithSHA384, ECDSAWithP384AndSHA384:
hash = crypto.SHA384
case PKCS1WithSHA512, PSSWithSHA512, ECDSAWithP521AndSHA512:
hash = crypto.SHA512
case Ed25519:
hash = directSigning
default:
return 0, 0, fmt.Errorf("unsupported signature algorithm: %v", signatureAlgorithm)
}
return sigType, hash, nil
}
// legacyTypeAndHashFromPublicKey returns the fixed signature type and crypto.Hash for
// a given public key used with TLS 1.0 and 1.1, before the introduction of
// signature algorithm negotiation.
func legacyTypeAndHashFromPublicKey(pub crypto.PublicKey) (sigType uint8, hash crypto.Hash, err error) {
switch pub.(type) {
case *rsa.PublicKey:
return signaturePKCS1v15, crypto.MD5SHA1, nil
case *ecdsa.PublicKey:
return signatureECDSA, crypto.SHA1, nil
case ed25519.PublicKey:
// RFC 8422 specifies support for Ed25519 in TLS 1.0 and 1.1,
// but it requires holding on to a handshake transcript to do a
// full signature, and not even OpenSSL bothers with the
// complexity, so we can't even test it properly.
return 0, 0, fmt.Errorf("tls: Ed25519 public keys are not supported before TLS 1.2")
default:
return 0, 0, fmt.Errorf("tls: unsupported public key: %T", pub)
}
}
var rsaSignatureSchemes = []struct {
scheme SignatureScheme
minModulusBytes int
}{
// RSA-PSS is used with PSSSaltLengthEqualsHash, and requires
// emLen >= hLen + sLen + 2
{PSSWithSHA256, crypto.SHA256.Size()*2 + 2},
{PSSWithSHA384, crypto.SHA384.Size()*2 + 2},
{PSSWithSHA512, crypto.SHA512.Size()*2 + 2},
// PKCS #1 v1.5 uses prefixes from hashPrefixes in crypto/rsa, and requires
// emLen >= len(prefix) + hLen + 11
{PKCS1WithSHA256, 19 + crypto.SHA256.Size() + 11},
{PKCS1WithSHA384, 19 + crypto.SHA384.Size() + 11},
{PKCS1WithSHA512, 19 + crypto.SHA512.Size() + 11},
{PKCS1WithSHA1, 15 + crypto.SHA1.Size() + 11},
}
func signatureSchemesForPublicKey(version uint16, pub crypto.PublicKey) []SignatureScheme {
switch pub := pub.(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:
size := pub.Size()
sigAlgs := make([]SignatureScheme, 0, len(rsaSignatureSchemes))
for _, candidate := range rsaSignatureSchemes {
if size >= candidate.minModulusBytes {
sigAlgs = append(sigAlgs, candidate.scheme)
}
}
return sigAlgs
case ed25519.PublicKey:
return []SignatureScheme{Ed25519}
default:
return nil
}
}
// selectSignatureScheme picks a SignatureScheme from the peer's preference list
// that works with the selected certificate. It's only called for protocol
// versions that support signature algorithms, so TLS 1.2 and 1.3.
func selectSignatureScheme(vers uint16, c *Certificate, peerAlgs []SignatureScheme) (SignatureScheme, error) {
priv, ok := c.PrivateKey.(crypto.Signer)
if !ok {
return 0, unsupportedCertificateError(c)
}
supportedAlgs := signatureSchemesForPublicKey(vers, priv.Public())
if c.SupportedSignatureAlgorithms != nil {
supportedAlgs = slices.DeleteFunc(supportedAlgs, func(sigAlg SignatureScheme) bool {
return !isSupportedSignatureAlgorithm(sigAlg, c.SupportedSignatureAlgorithms)
})
}
// Filter out any unsupported signature algorithms, for example due to
// FIPS 140-3 policy, tlssha1=0, or protocol version.
supportedAlgs = slices.DeleteFunc(supportedAlgs, func(sigAlg SignatureScheme) bool {
return isDisabledSignatureAlgorithm(vers, sigAlg, false)
})
if len(supportedAlgs) == 0 {
return 0, unsupportedCertificateError(c)
}
if len(peerAlgs) == 0 && vers == VersionTLS12 {
// For TLS 1.2, if the client didn't send signature_algorithms then we
// can assume that it supports SHA1. See RFC 5246, Section 7.4.1.4.1.
// RFC 9155 made signature_algorithms mandatory in TLS 1.2, and we gated
// it behind the tlssha1 GODEBUG setting.
if tlssha1.Value() != "1" {
return 0, errors.New("tls: missing signature_algorithms from TLS 1.2 peer")
}
peerAlgs = []SignatureScheme{PKCS1WithSHA1, ECDSAWithSHA1}
}
// Pick signature scheme in the peer's preference order, as our
// preference order is not configurable.
for _, preferredAlg := range peerAlgs {
if isSupportedSignatureAlgorithm(preferredAlg, supportedAlgs) {
return preferredAlg, nil
}
}
return 0, errors.New("tls: peer doesn't support any of the certificate's signature algorithms")
}
// 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)
case *ed25519.PrivateKey:
return fmt.Errorf("tls: unsupported certificate: private key is *ed25519.PrivateKey, expected ed25519.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:
return fmt.Errorf("tls: certificate RSA key size too small for supported signature algorithms")
case ed25519.PublicKey:
default:
return fmt.Errorf("tls: unsupported certificate key (%T)", pub)
}
if cert.SupportedSignatureAlgorithms != nil {
return fmt.Errorf("tls: peer doesn't support the certificate custom signature algorithms")
}
return fmt.Errorf("tls: internal error: unsupported key (%T)", cert.PrivateKey)
}
