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crypto/tls: clarify TLS 1.0/1.1 CertificateRequestInfo.SignatureSchemes

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This CL should not change the logic at all, but it took me a while to
figure out why we use these specific SignatureSchemes, so reformulate
the comment.

Change-Id: If519a58264209e6575417be07668e92ead0e772f
Reviewed-on: https://go-review.googlesource.com/c/go/+/208225
Run-TryBot: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Katie Hockman <katie@golang.org>
This commit is contained in:
Filippo Valsorda 2019-11-21 13:48:38 -05:00
parent 3e4e644433
commit 4045de378b
1 changed files with 15 additions and 15 deletions
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30
src/crypto/tls/handshake_client.go
View file

@ -839,14 +839,6 @@ func (c *Conn) verifyServerCertificate(certificates [][]byte) error {
return nil
}
// tls11SignatureSchemes contains the signature schemes that we synthesise for
// a TLS <= 1.1 connection, based on the supported certificate types.
var (
tls11SignatureSchemes = []SignatureScheme{ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512, PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1}
tls11SignatureSchemesECDSA = tls11SignatureSchemes[:3]
tls11SignatureSchemesRSA = tls11SignatureSchemes[3:]
)
// certificateRequestInfoFromMsg generates a CertificateRequestInfo from a TLS
// <= 1.2 CertificateRequest, making an effort to fill in missing information.
func certificateRequestInfoFromMsg(vers uint16, certReq *certificateRequestMsg) *CertificateRequestInfo {
@ -866,17 +858,25 @@ func certificateRequestInfoFromMsg(vers uint16, certReq *certificateRequestMsg)
}
if !certReq.hasSignatureAlgorithm {
// Prior to TLS 1.2, the signature schemes were not
// included in the certificate request message. In this
// case we use a plausible list based on the acceptable
// certificate types.
// Prior to TLS 1.2, signature schemes did not exist. In this case we
// make up a list based on the acceptable certificate types, to help
// GetClientCertificate and SupportsCertificate select the right certificate.
// The hash part of the SignatureScheme is a lie here, because
// TLS 1.0 and 1.1 always use MD5+SHA1 for RSA and SHA1 for ECDSA.
switch {
case rsaAvail && ecAvail:
cri.SignatureSchemes = tls11SignatureSchemes
cri.SignatureSchemes = []SignatureScheme{
ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512,
PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1,
}
case rsaAvail:
cri.SignatureSchemes = tls11SignatureSchemesRSA
cri.SignatureSchemes = []SignatureScheme{
PKCS1WithSHA256, PKCS1WithSHA384, PKCS1WithSHA512, PKCS1WithSHA1,
}
case ecAvail:
cri.SignatureSchemes = tls11SignatureSchemesECDSA
cri.SignatureSchemes = []SignatureScheme{
ECDSAWithP256AndSHA256, ECDSAWithP384AndSHA384, ECDSAWithP521AndSHA512,
}
}
return cri
}