ssh: support rsa-sha2-256/512 for client certificates
The server-sig-algs logic was not working for certificate algorithms.
Follow-up on CL 392394.
Tested with OpenSSH 8.8 configured with
PubkeyAcceptedKeyTypes -ssh-rsa-cert-v01@openssh.com
Updates golang/go#39885
For golang/go#49952
Change-Id: Ic230dd6f98e96b7938acbd0128ab37d33b70abe5
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/392974
Trust: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
diff --git a/ssh/certs.go b/ssh/certs.go
index c7a4dd0..a69e224 100644
--- a/ssh/certs.go
+++ b/ssh/certs.go
@@ -483,6 +483,17 @@
return algo
}
+// certificateAlgo returns the certificate algorithms that uses the provided
+// underlying signature algorithm.
+func certificateAlgo(algo string) (certAlgo string, ok bool) {
+ for certName, algoName := range certKeyAlgoNames {
+ if algoName == algo {
+ return certName, true
+ }
+ }
+ return "", false
+}
+
func (cert *Certificate) bytesForSigning() []byte {
c2 := *cert
c2.Signature = nil
@@ -526,13 +537,11 @@
// Type returns the certificate algorithm name. It is part of the PublicKey interface.
func (c *Certificate) Type() string {
- keyType := c.Key.Type()
- for certName, keyName := range certKeyAlgoNames {
- if keyName == keyType {
- return certName
- }
+ certName, ok := certificateAlgo(c.Key.Type())
+ if !ok {
+ panic("unknown certificate type for key type " + c.Key.Type())
}
- panic("unknown certificate type for key type " + keyType)
+ return certName
}
// Verify verifies a signature against the certificate's public
diff --git a/ssh/client_auth.go b/ssh/client_auth.go
index a962a67..409b5ea 100644
--- a/ssh/client_auth.go
+++ b/ssh/client_auth.go
@@ -234,7 +234,17 @@
return as, keyFormat
}
+ // The server-sig-algs extension only carries underlying signature
+ // algorithm, but we are trying to select a protocol-level public key
+ // algorithm, which might be a certificate type. Extend the list of server
+ // supported algorithms to include the corresponding certificate algorithms.
serverAlgos := strings.Split(string(extPayload), ",")
+ for _, algo := range serverAlgos {
+ if certAlgo, ok := certificateAlgo(algo); ok {
+ serverAlgos = append(serverAlgos, certAlgo)
+ }
+ }
+
keyAlgos := algorithmsForKeyFormat(keyFormat)
algo, err := findCommon("public key signature algorithm", keyAlgos, serverAlgos)
if err != nil {
