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crypto/tls: implement Certificate.SupportedSignatureAlgorithms

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This will let applications stop crypto/tls from using a certificate key
with an algorithm that is not supported by its crypto.Signer, like
hardware backed keys that can't do RSA-PSS.

Fixes #28660

Change-Id: I294cc06bddf813fff35c5107540c4a1788e1dace
Reviewed-on: https://go-review.googlesource.com/c/go/+/205062
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Adam Langley <agl@golang.org>
This commit is contained in:
Filippo Valsorda 2019-11-03 21:04:48 -05:00
parent 0e7f9b3702
commit 555e9b864b
4 changed files with 91 additions and 9 deletions
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37
auth.go
View file

@ -154,7 +154,8 @@ func legacyTypeAndHashFromPublicKey(pub crypto.PublicKey) (sigType uint8, hash c
}
// signatureSchemesForCertificate returns the list of supported SignatureSchemes
// for a given certificate, based on the public key and the protocol version.
// for a given certificate, based on the public key and the protocol version,
// and optionally filtered by its explicit SupportedSignatureAlgorithms.
//
// This function must be kept in sync with supportedSignatureAlgorithms.
func signatureSchemesForCertificate(version uint16, cert *Certificate) []SignatureScheme {
@ -163,31 +164,33 @@ func signatureSchemesForCertificate(version uint16, cert *Certificate) []Signatu
return nil
}
var sigAlgs []SignatureScheme
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{
sigAlgs = []SignatureScheme{
ECDSAWithP256AndSHA256,
ECDSAWithP384AndSHA384,
ECDSAWithP521AndSHA512,
ECDSAWithSHA1,
}
break
}
switch pub.Curve {
case elliptic.P256():
return []SignatureScheme{ECDSAWithP256AndSHA256}
sigAlgs = []SignatureScheme{ECDSAWithP256AndSHA256}
case elliptic.P384():
return []SignatureScheme{ECDSAWithP384AndSHA384}
sigAlgs = []SignatureScheme{ECDSAWithP384AndSHA384}
case elliptic.P521():
return []SignatureScheme{ECDSAWithP521AndSHA512}
sigAlgs = []SignatureScheme{ECDSAWithP521AndSHA512}
default:
return nil
}
case *rsa.PublicKey:
if version != VersionTLS13 {
return []SignatureScheme{
sigAlgs = []SignatureScheme{
// Temporarily disable RSA-PSS in TLS 1.2, see Issue 32425.
// PSSWithSHA256,
// PSSWithSHA384,
@ -197,18 +200,30 @@ func signatureSchemesForCertificate(version uint16, cert *Certificate) []Signatu
PKCS1WithSHA512,
PKCS1WithSHA1,
}
break
}
// TLS 1.3 dropped support for PKCS#1 v1.5 in favor of RSA-PSS.
return []SignatureScheme{
sigAlgs = []SignatureScheme{
PSSWithSHA256,
PSSWithSHA384,
PSSWithSHA512,
}
case ed25519.PublicKey:
return []SignatureScheme{Ed25519}
sigAlgs = []SignatureScheme{Ed25519}
default:
return nil
}
if cert.SupportedSignatureAlgorithms != nil {
var filteredSigAlgs []SignatureScheme
for _, sigAlg := range sigAlgs {
if isSupportedSignatureAlgorithm(sigAlg, cert.SupportedSignatureAlgorithms) {
filteredSigAlgs = append(filteredSigAlgs, sigAlg)
}
}
return filteredSigAlgs
}
return sigAlgs
}
// selectSignatureScheme picks a SignatureScheme from the peer's preference list
@ -216,7 +231,7 @@ func signatureSchemesForCertificate(version uint16, cert *Certificate) []Signatu
// versions that support signature algorithms, so TLS 1.2 and 1.3.
func selectSignatureScheme(vers uint16, c *Certificate, peerAlgs []SignatureScheme) (SignatureScheme, error) {
supportedAlgs := signatureSchemesForCertificate(vers, c)
if supportedAlgs == nil {
if len(supportedAlgs) == 0 {
return 0, unsupportedCertificateError(c)
}
if len(peerAlgs) == 0 && vers == VersionTLS12 {
@ -266,5 +281,9 @@ func unsupportedCertificateError(cert *Certificate) error {
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)
}