Add support for ssh commit signing (#17743)

* Add support for ssh commit signing

* Split out ssh verification to separate file

* Show ssh key fingerprint on commit page

* Update sshsig lib

* Make sure we verify against correct namespace

* Add ssh public key verification via ssh signatures

When adding a public ssh key also validate that this user actually
owns the key by signing a token with the private key.

* Remove some gpg references and make verify key optional

* Fix spaces indentation

* Update options/locale/locale_en-US.ini

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update templates/user/settings/keys_ssh.tmpl

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update options/locale/locale_en-US.ini

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update options/locale/locale_en-US.ini

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Update models/ssh_key_commit_verification.go

Co-authored-by: Gusted <williamzijl7@hotmail.com>

* Reword ssh/gpg_key_success message

* Change Badsignature to NoKeyFound

* Add sign/verify tests

* Fix upstream api changes to user_model User

* Match exact on SSH signature

* Fix code review remarks

Co-authored-by: Gusted <williamzijl7@hotmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

vendor/golang.org/x/crypto/ssh/certs.go

@@ -14,7 +14,7 @@ import (
 	"time"
 )
 
-// These constants from [PROTOCOL.certkeys] represent the algorithm names
+// These constants from [PROTOCOL.certkeys] represent the key algorithm names
 // for certificate types supported by this package.
 const (
 	CertAlgoRSAv01        = "ssh-rsa-cert-v01@openssh.com"
@@ -27,6 +27,14 @@ const (
 	CertAlgoSKED25519v01  = "sk-ssh-ed25519-cert-v01@openssh.com"
 )
 
+// These constants from [PROTOCOL.certkeys] represent additional signature
+// algorithm names for certificate types supported by this package.
+const (
+	CertSigAlgoRSAv01        = "ssh-rsa-cert-v01@openssh.com"
+	CertSigAlgoRSASHA2256v01 = "rsa-sha2-256-cert-v01@openssh.com"
+	CertSigAlgoRSASHA2512v01 = "rsa-sha2-512-cert-v01@openssh.com"
+)
+
 // Certificate types distinguish between host and user
 // certificates. The values can be set in the CertType field of
 // Certificate.
@@ -423,6 +431,12 @@ func (c *Certificate) SignCert(rand io.Reader, authority Signer) error {
 	}
 	c.SignatureKey = authority.PublicKey()
 
+	if v, ok := authority.(AlgorithmSigner); ok {
+		if v.PublicKey().Type() == KeyAlgoRSA {
+			authority = &rsaSigner{v, SigAlgoRSASHA2512}
+		}
+	}
+
 	sig, err := authority.Sign(rand, c.bytesForSigning())
 	if err != nil {
 		return err
@@ -431,8 +445,14 @@ func (c *Certificate) SignCert(rand io.Reader, authority Signer) error {
 	return nil
 }
 
+// certAlgoNames includes a mapping from signature algorithms to the
+// corresponding certificate signature algorithm. When a key type (such
+// as ED25516) is associated with only one algorithm, the KeyAlgo
+// constant is used instead of the SigAlgo.
 var certAlgoNames = map[string]string{
-	KeyAlgoRSA:        CertAlgoRSAv01,
+	SigAlgoRSA:        CertSigAlgoRSAv01,
+	SigAlgoRSASHA2256: CertSigAlgoRSASHA2256v01,
+	SigAlgoRSASHA2512: CertSigAlgoRSASHA2512v01,
 	KeyAlgoDSA:        CertAlgoDSAv01,
 	KeyAlgoECDSA256:   CertAlgoECDSA256v01,
 	KeyAlgoECDSA384:   CertAlgoECDSA384v01,

vendor/golang.org/x/crypto/ssh/cipher.go

@@ -18,7 +18,7 @@ import (
 	"io/ioutil"
 
 	"golang.org/x/crypto/chacha20"
-	"golang.org/x/crypto/poly1305"
+	"golang.org/x/crypto/internal/poly1305"
 )
 
 const (

vendor/golang.org/x/crypto/ssh/client.go

@@ -115,12 +115,25 @@ func (c *connection) clientHandshake(dialAddress string, config *ClientConfig) e
 
 // verifyHostKeySignature verifies the host key obtained in the key
 // exchange.
-func verifyHostKeySignature(hostKey PublicKey, result *kexResult) error {
+func verifyHostKeySignature(hostKey PublicKey, algo string, result *kexResult) error {
 	sig, rest, ok := parseSignatureBody(result.Signature)
 	if len(rest) > 0 || !ok {
 		return errors.New("ssh: signature parse error")
 	}
 
+	// For keys, underlyingAlgo is exactly algo. For certificates,
+	// we have to look up the underlying key algorithm that SSH
+	// uses to evaluate signatures.
+	underlyingAlgo := algo
+	for sigAlgo, certAlgo := range certAlgoNames {
+		if certAlgo == algo {
+			underlyingAlgo = sigAlgo
+		}
+	}
+	if sig.Format != underlyingAlgo {
+		return fmt.Errorf("ssh: invalid signature algorithm %q, expected %q", sig.Format, underlyingAlgo)
+	}
+
 	return hostKey.Verify(result.H, sig)
 }
 

vendor/golang.org/x/crypto/ssh/common.go

@@ -69,11 +69,13 @@ var preferredKexAlgos = []string{
 // supportedHostKeyAlgos specifies the supported host-key algorithms (i.e. methods
 // of authenticating servers) in preference order.
 var supportedHostKeyAlgos = []string{
-	CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01,
+	CertSigAlgoRSASHA2512v01, CertSigAlgoRSASHA2256v01,
+	CertSigAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01,
 	CertAlgoECDSA384v01, CertAlgoECDSA521v01, CertAlgoED25519v01,
 
 	KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521,
-	KeyAlgoRSA, KeyAlgoDSA,
+	SigAlgoRSASHA2512, SigAlgoRSASHA2256,
+	SigAlgoRSA, KeyAlgoDSA,
 
 	KeyAlgoED25519,
 }
@@ -90,16 +92,20 @@ var supportedCompressions = []string{compressionNone}
 // hashFuncs keeps the mapping of supported algorithms to their respective
 // hashes needed for signature verification.
 var hashFuncs = map[string]crypto.Hash{
-	KeyAlgoRSA:          crypto.SHA1,
-	KeyAlgoDSA:          crypto.SHA1,
-	KeyAlgoECDSA256:     crypto.SHA256,
-	KeyAlgoECDSA384:     crypto.SHA384,
-	KeyAlgoECDSA521:     crypto.SHA512,
-	CertAlgoRSAv01:      crypto.SHA1,
-	CertAlgoDSAv01:      crypto.SHA1,
-	CertAlgoECDSA256v01: crypto.SHA256,
-	CertAlgoECDSA384v01: crypto.SHA384,
-	CertAlgoECDSA521v01: crypto.SHA512,
+	SigAlgoRSA:               crypto.SHA1,
+	SigAlgoRSASHA2256:        crypto.SHA256,
+	SigAlgoRSASHA2512:        crypto.SHA512,
+	KeyAlgoDSA:               crypto.SHA1,
+	KeyAlgoECDSA256:          crypto.SHA256,
+	KeyAlgoECDSA384:          crypto.SHA384,
+	KeyAlgoECDSA521:          crypto.SHA512,
+	CertSigAlgoRSAv01:        crypto.SHA1,
+	CertSigAlgoRSASHA2256v01: crypto.SHA256,
+	CertSigAlgoRSASHA2512v01: crypto.SHA512,
+	CertAlgoDSAv01:           crypto.SHA1,
+	CertAlgoECDSA256v01:      crypto.SHA256,
+	CertAlgoECDSA384v01:      crypto.SHA384,
+	CertAlgoECDSA521v01:      crypto.SHA512,
 }
 
 // unexpectedMessageError results when the SSH message that we received didn't

vendor/golang.org/x/crypto/ssh/handshake.go

@@ -457,8 +457,15 @@ func (t *handshakeTransport) sendKexInit() error {
 
 	if len(t.hostKeys) > 0 {
 		for _, k := range t.hostKeys {
-			msg.ServerHostKeyAlgos = append(
-				msg.ServerHostKeyAlgos, k.PublicKey().Type())
+			algo := k.PublicKey().Type()
+			switch algo {
+			case KeyAlgoRSA:
+				msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, []string{SigAlgoRSASHA2512, SigAlgoRSASHA2256, SigAlgoRSA}...)
+			case CertAlgoRSAv01:
+				msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, []string{CertSigAlgoRSASHA2512v01, CertSigAlgoRSASHA2256v01, CertSigAlgoRSAv01}...)
+			default:
+				msg.ServerHostKeyAlgos = append(msg.ServerHostKeyAlgos, algo)
+			}
 		}
 	} else {
 		msg.ServerHostKeyAlgos = t.hostKeyAlgorithms
@@ -614,8 +621,22 @@ func (t *handshakeTransport) enterKeyExchange(otherInitPacket []byte) error {
 func (t *handshakeTransport) server(kex kexAlgorithm, algs *algorithms, magics *handshakeMagics) (*kexResult, error) {
 	var hostKey Signer
 	for _, k := range t.hostKeys {
-		if algs.hostKey == k.PublicKey().Type() {
+		kt := k.PublicKey().Type()
+		if kt == algs.hostKey {
 			hostKey = k
+		} else if signer, ok := k.(AlgorithmSigner); ok {
+			// Some signature algorithms don't show up as key types
+			// so we have to manually check for a compatible host key.
+			switch kt {
+			case KeyAlgoRSA:
+				if algs.hostKey == SigAlgoRSASHA2256 || algs.hostKey == SigAlgoRSASHA2512 {
+					hostKey = &rsaSigner{signer, algs.hostKey}
+				}
+			case CertAlgoRSAv01:
+				if algs.hostKey == CertSigAlgoRSASHA2256v01 || algs.hostKey == CertSigAlgoRSASHA2512v01 {
+					hostKey = &rsaSigner{signer, certToPrivAlgo(algs.hostKey)}
+				}
+			}
 		}
 	}
 
@@ -634,7 +655,7 @@ func (t *handshakeTransport) client(kex kexAlgorithm, algs *algorithms, magics *
 		return nil, err
 	}
 
-	if err := verifyHostKeySignature(hostKey, result); err != nil {
+	if err := verifyHostKeySignature(hostKey, algs.hostKey, result); err != nil {
 		return nil, err
 	}
 

vendor/golang.org/x/crypto/ssh/keys.go

@@ -939,6 +939,15 @@ func newDSAPrivateKey(key *dsa.PrivateKey) (Signer, error) {
 	return &dsaPrivateKey{key}, nil
 }
 
+type rsaSigner struct {
+	AlgorithmSigner
+	defaultAlgorithm string
+}
+
+func (s *rsaSigner) Sign(rand io.Reader, data []byte) (*Signature, error) {
+	return s.AlgorithmSigner.SignWithAlgorithm(rand, data, s.defaultAlgorithm)
+}
+
 type wrappedSigner struct {
 	signer crypto.Signer
 	pubKey PublicKey

vendor/golang.org/x/crypto/ssh/server.go

@@ -284,7 +284,7 @@ func (s *connection) serverHandshake(config *ServerConfig) (*Permissions, error)
 
 func isAcceptableAlgo(algo string) bool {
 	switch algo {
-	case KeyAlgoRSA, KeyAlgoDSA, KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521, KeyAlgoSKECDSA256, KeyAlgoED25519, KeyAlgoSKED25519,
+	case SigAlgoRSA, SigAlgoRSASHA2256, SigAlgoRSASHA2512, KeyAlgoDSA, KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521, KeyAlgoSKECDSA256, KeyAlgoED25519, KeyAlgoSKED25519,
 		CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01, CertAlgoECDSA384v01, CertAlgoECDSA521v01, CertAlgoSKECDSA256v01, CertAlgoED25519v01, CertAlgoSKED25519v01:
 		return true
 	}