Adding support for OpenSSH ecdsa-sk & ed25519-sk public keys

src/cryptography/hazmat/primitives/serialization/ssh.py

@@ -64,6 +64,10 @@ def _bcrypt_kdf(
 _ECDSA_NISTP521 = b"ecdsa-sha2-nistp521"
 _CERT_SUFFIX = b"-cert-v01@openssh.com"
 
+# U2F application string suffixed pubkey
+_SK_SSH_ED25519 = b"sk-ssh-ed25519@openssh.com"
+_SK_SSH_ECDSA_NISTP256 = b"sk-ecdsa-sha2-nistp256@openssh.com"
+
 # These are not key types, only algorithms, so they cannot appear
 # as a public key type
 _SSH_RSA_SHA256 = b"rsa-sha2-256"
@@ -572,13 +576,65 @@ def encode_private(
         f_priv.put_sshstr(f_keypair)
 
 
+def load_application(data) -> tuple[memoryview, memoryview]:
+    """
+    U2F application strings
+    """
+    application, data = _get_sshstr(data)
+    if not application.tobytes().startswith(b"ssh:"):
+        raise ValueError(
+            "U2F application string does not start with b'ssh:' "
+            f"({application})"
+        )
+    return application, data
+
+
+class _SSHFormatSKEd25519:
+    """
+    The format of a sk-ssh-ed25519@openssh.com public key is:
+
+        string		"sk-ssh-ed25519@openssh.com"
+        string		public key
+        string		application (user-specified, but typically "ssh:")
+    """
+
+    def load_public(
+        self, data: memoryview
+    ) -> tuple[ed25519.Ed25519PublicKey, memoryview]:
+        """Make Ed25519 public key from data."""
+        public_key, data = _lookup_kformat(_SSH_ED25519).load_public(data)
+        application, data = load_application(data)
+        return public_key, data
+
+
+class _SSHFormatSKECDSA:
+    """
+    The format of a sk-ecdsa-sha2-nistp256@openssh.com public key is:
+
+        string		"sk-ecdsa-sha2-nistp256@openssh.com"
+        string		curve name
+        ec_point	Q
+        string		application (user-specified, but typically "ssh:")
+    """
+
+    def load_public(
+        self, data: memoryview
+    ) -> tuple[ec.EllipticCurvePublicKey, memoryview]:
+        """Make Ed25519 public key from data."""
+        public_key, data = _lookup_kformat(_ECDSA_NISTP256).load_public(data)
+        application, data = load_application(data)
+        return public_key, data
+
+
 _KEY_FORMATS = {
     _SSH_RSA: _SSHFormatRSA(),
     _SSH_DSA: _SSHFormatDSA(),
     _SSH_ED25519: _SSHFormatEd25519(),
     _ECDSA_NISTP256: _SSHFormatECDSA(b"nistp256", ec.SECP256R1()),
     _ECDSA_NISTP384: _SSHFormatECDSA(b"nistp384", ec.SECP384R1()),
     _ECDSA_NISTP521: _SSHFormatECDSA(b"nistp521", ec.SECP521R1()),
+    _SK_SSH_ED25519: _SSHFormatSKEd25519(),
+    _SK_SSH_ECDSA_NISTP256: _SSHFormatSKECDSA(),
 }
 
 

tests/hazmat/primitives/test_ssh.py

@@ -55,6 +55,10 @@ class TestOpenSSHSerialization:
             ("ecdsa-nopsw.key.pub", "ecdsa-nopsw.key-cert.pub"),
             ("ed25519-psw.key.pub", None),
             ("ed25519-nopsw.key.pub", "ed25519-nopsw.key-cert.pub"),
+            ("sk-ecdsa-psw.key.pub", None),
+            ("sk-ecdsa-nopsw.key.pub", None),
+            ("sk-ed25519-psw.key.pub", None),
+            ("sk-ed25519-nopsw.key.pub", None),
         ],
     )
     def test_load_ssh_public_key(self, key_file, cert_file, backend):
@@ -80,10 +84,14 @@ def test_load_ssh_public_key(self, key_file, cert_file, backend):
                 )
         else:
             public_key = load_ssh_public_key(pub_data, backend)
-            assert (
-                public_key.public_bytes(Encoding.OpenSSH, PublicFormat.OpenSSH)
-                == nocomment_data
-            )
+            if not key_file.startswith("sk-"):
+                # SK keys do not round-trip
+                assert (
+                    public_key.public_bytes(
+                        Encoding.OpenSSH, PublicFormat.OpenSSH
+                    )
+                    == nocomment_data
+                )
 
         self.run_partial_pubkey(pub_data, backend)
 
@@ -1800,3 +1808,20 @@ def test_sign_and_byte_compare_ed25519(self, monkeypatch, backend):
             b"t8yRa8IRbxvOyA9TZYDGG1dRE3DiR0fuudU20v6vqfTd1gx0S5QyEdECXLl9ZI3"
             b"AwZgc="
         )
+
+
+class TestSSHSK:
+    @staticmethod
+    def ssh_str(application):
+        data = (
+            len(application).to_bytes(length=4, byteorder="big")
+            + application.encode()
+        )
+        return memoryview(data)
+
+    def test_load_application(self):
+        ssh.load_application(self.ssh_str("ssh:test"))
+
+    def test_load_application_valueerror(self):
+        with pytest.raises(ValueError):
+            ssh.load_application(self.ssh_str("hss:test"))

vectors/cryptography_vectors/asymmetric/OpenSSH/gen.sh

@@ -19,10 +19,13 @@ getecbits() {
 genkey() {
     fn="$1"
     args="-f $fn -C $fn"
+    sk="-O application=ssh:the-application-string"
     case "$fn" in
+    sk-ecdsa-*) args="$args -t ecdsa-sk -b $(getecbits) $sk" ;;
     ecdsa-*) args="$args -t ecdsa -b $(getecbits)" ;;
     rsa-*) args="$args -t rsa" ;;
     dsa-*) args="$args -t dsa" ;;
+    sk-ed25519-*) args="$args -t ed25519-sk $sk" ;;
     ed25519-*) args="$args -t ed25519" ;;
     esac
     password=''
@@ -33,12 +36,13 @@ genkey() {
 }
 
 # generate private key files
-for ktype in rsa dsa ecdsa ed25519; do
+for ktype in rsa dsa ecdsa sk-ecdsa ed25519 sk-ed25519; do
     for psw in nopsw psw; do
         genkey "${ktype}-${psw}.key"
     done
 done
 
+
 # generate public key files
 for fn in *.key; do
   ssh-keygen -q -y -f "$fn" > /dev/null

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ecdsa-nopsw.key

@@ -0,0 +1,11 @@
+-----BEGIN OPENSSH PRIVATE KEY-----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+-----END OPENSSH PRIVATE KEY-----

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ecdsa-nopsw.key.pub

@@ -0,0 +1 @@
+sk-ecdsa-sha2-nistp256@openssh.com AAAAInNrLWVjZHNhLXNoYTItbmlzdHAyNTZAb3BlbnNzaC5jb20AAAAIbmlzdHAyNTYAAABBBDte6cjxBF+bJPQ8pYle1oTSUDr4fLkdN8gN8d7GxlXrwAYCPSdjJ/b6YAr+8+nojJUEAsmp3N0liLJ5en/ed4sAAAAac3NoOnRoZS1hcHBsaWNhdGlvbi1zdHJpbmc= sk-ecdsa-nopsw.key

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ecdsa-psw.key

@@ -0,0 +1,12 @@
+-----BEGIN OPENSSH PRIVATE KEY-----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+-----END OPENSSH PRIVATE KEY-----

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ecdsa-psw.key.pub

@@ -0,0 +1 @@
+sk-ecdsa-sha2-nistp256@openssh.com AAAAInNrLWVjZHNhLXNoYTItbmlzdHAyNTZAb3BlbnNzaC5jb20AAAAIbmlzdHAyNTYAAABBBACdJuKxgDLk+a1NeeCtRqCropd0hXume/cTdOvV/B4lmupr9viNQsUT09wbKRflnOc9jxPAiQOzZbXTkmnV8kkAAAAac3NoOnRoZS1hcHBsaWNhdGlvbi1zdHJpbmc= sk-ecdsa-psw.key

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ed25519-nopsw.key

@@ -0,0 +1,10 @@
+-----BEGIN OPENSSH PRIVATE KEY-----
+b3BlbnNzaC1rZXktdjEAAAAABG5vbmUAAAAEbm9uZQAAAAAAAAABAAAAYAAAABpzay1zc2
+gtZWQyNTUxOUBvcGVuc3NoLmNvbQAAACB6auRr7BwVOqTawgDOxUpaUFcN8SZ7SWzoR2Vs
+ubbk3wAAABpzc2g6dGhlLWFwcGxpY2F0aW9uLXN0cmluZwAAARCWIPLyliDy8gAAABpzay
+1zc2gtZWQyNTUxOUBvcGVuc3NoLmNvbQAAACB6auRr7BwVOqTawgDOxUpaUFcN8SZ7SWzo
+R2Vsubbk3wAAABpzc2g6dGhlLWFwcGxpY2F0aW9uLXN0cmluZwEAAACAQPv/aY2F3YN1kD
+1FHPa1HpEHOGAbsYj/2b6h8Rn+N4pU6hdTD5v19Efdz5jlt8Y84c61+8HKDPCI/g5Cbcvd
+3uuGHuFUdgiarOZqKyuwBj3Kll9Whb/yV4wGo/NVXtCHa2SnWr2wjYtRTGPNNCgGPsLU05
+/KTNCStsNhEcsNDjEAAAAAAAAAFHNrLWVkMjU1MTktbm9wc3cua2V5AQIDBAUGBw==
+-----END OPENSSH PRIVATE KEY-----

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ed25519-nopsw.key.pub

@@ -0,0 +1 @@
+sk-ssh-ed25519@openssh.com AAAAGnNrLXNzaC1lZDI1NTE5QG9wZW5zc2guY29tAAAAIHpq5GvsHBU6pNrCAM7FSlpQVw3xJntJbOhHZWy5tuTfAAAAGnNzaDp0aGUtYXBwbGljYXRpb24tc3RyaW5n sk-ed25519-nopsw.key

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ed25519-psw.key

@@ -0,0 +1,11 @@
+-----BEGIN OPENSSH PRIVATE KEY-----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+-----END OPENSSH PRIVATE KEY-----

vectors/cryptography_vectors/asymmetric/OpenSSH/sk-ed25519-psw.key.pub

@@ -0,0 +1 @@
+sk-ssh-ed25519@openssh.com AAAAGnNrLXNzaC1lZDI1NTE5QG9wZW5zc2guY29tAAAAIHf0iiNQTiR7NNAbeAwY+READVx9G0mP6idSAZ7bPTrMAAAAGnNzaDp0aGUtYXBwbGljYXRpb24tc3RyaW5n sk-ed25519-psw.key