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ssh: add MultiAlgorithmSigner

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MultiAlgorithmSigner allows to restrict client-side, server-side and
certificate signing algorithms.

Fixes golang/go#52132
Fixes golang/go#36261

Change-Id: I295092f1bba647327aaaf294f110e9157d294159
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/508398
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Run-TryBot: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
This commit is contained in:
Nicola Murino
2023-09-20 18:10:30 +00:00
committed by Gopher Robot
parent 3f0842a464
commit 28c53ff63c
9 changed files with 554 additions and 66 deletions
Download Patch File Download Diff File Expand all files Collapse all files
ssh/certs.go
+30 -8
View File
@@ -16,8 +16,9 @@ import (
// Certificate algorithm names from [PROTOCOL.certkeys]. These values can appear
// in Certificate.Type, PublicKey.Type, and ClientConfig.HostKeyAlgorithms.
// Unlike key algorithm names, these are not passed to AlgorithmSigner and don't
// appear in the Signature.Format field.
// Unlike key algorithm names, these are not passed to AlgorithmSigner nor
// returned by MultiAlgorithmSigner and don't appear in the Signature.Format
// field.
const (
CertAlgoRSAv01 = "ssh-rsa-cert-v01@openssh.com"
CertAlgoDSAv01 = "ssh-dss-cert-v01@openssh.com"
@@ -255,10 +256,17 @@ func NewCertSigner(cert *Certificate, signer Signer) (Signer, error) {
return nil, errors.New("ssh: signer and cert have different public key")
}
if algorithmSigner, ok := signer.(AlgorithmSigner); ok {
switch s := signer.(type) {
case MultiAlgorithmSigner:
return &multiAlgorithmSigner{
AlgorithmSigner: &algorithmOpenSSHCertSigner{
&openSSHCertSigner{cert, signer}, s},
supportedAlgorithms: s.Algorithms(),
}, nil
case AlgorithmSigner:
return &algorithmOpenSSHCertSigner{
&openSSHCertSigner{cert, signer}, algorithmSigner}, nil
} else {
&openSSHCertSigner{cert, signer}, s}, nil
default:
return &openSSHCertSigner{cert, signer}, nil
}
}
@@ -432,7 +440,9 @@ func (c *CertChecker) CheckCert(principal string, cert *Certificate) error {
}
// SignCert signs the certificate with an authority, setting the Nonce,
// SignatureKey, and Signature fields.
// SignatureKey, and Signature fields. If the authority implements the
// MultiAlgorithmSigner interface the first algorithm in the list is used. This
// is useful if you want to sign with a specific algorithm.
func (c *Certificate) SignCert(rand io.Reader, authority Signer) error {
c.Nonce = make([]byte, 32)
if _, err := io.ReadFull(rand, c.Nonce); err != nil {
@@ -440,8 +450,20 @@ func (c *Certificate) SignCert(rand io.Reader, authority Signer) error {
}
c.SignatureKey = authority.PublicKey()
// Default to KeyAlgoRSASHA512 for ssh-rsa signers.
if v, ok := authority.(AlgorithmSigner); ok && v.PublicKey().Type() == KeyAlgoRSA {
if v, ok := authority.(MultiAlgorithmSigner); ok {
if len(v.Algorithms()) == 0 {
return errors.New("the provided authority has no signature algorithm")
}
// Use the first algorithm in the list.
sig, err := v.SignWithAlgorithm(rand, c.bytesForSigning(), v.Algorithms()[0])
if err != nil {
return err
}
c.Signature = sig
return nil
} else if v, ok := authority.(AlgorithmSigner); ok && v.PublicKey().Type() == KeyAlgoRSA {
// Default to KeyAlgoRSASHA512 for ssh-rsa signers.
// TODO: consider using KeyAlgoRSASHA256 as default.
sig, err := v.SignWithAlgorithm(rand, c.bytesForSigning(), KeyAlgoRSASHA512)
if err != nil {
return err