add secp256k1 key pair type

Author: kenta-wakasa

cryptography/lib/src/cryptography/key_pair_type.dart

@@ -35,6 +35,15 @@ class KeyPairType<S extends KeyPairData, P extends PublicKey> {
     webCryptoCurve: 'P-256',
   );
 
+  /// Key pair type for [Ecdh] and [Ecdsa] with P-256 curve.
+  ///
+  /// Keys of this type can be generated with [EcKeyPairGenerator].
+  static const KeyPairType p256k = KeyPairType<EcKeyPairData, EcPublicKey>._(
+    name: 'p256k',
+    ellipticBits: 256,
+    webCryptoCurve: 'P-256K',
+  );
+
   /// Key pair type for [Ecdh] and [Ecdsa] with P-384 curve.
   ///
   /// Keys of this type can be generated with [EcKeyPairGenerator].

jwk/lib/jwk.dart

@@ -606,6 +606,7 @@ class Jwk {
     if (publicKey is EcPublicKey) {
       final crv = const <KeyPairType, String>{
         KeyPairType.p256: 'P-256',
+        KeyPairType.p256k: 'secp256k1',
         KeyPairType.p384: 'P-384',
         KeyPairType.p521: 'P-521',
       }[publicKey.type];