[#2] Add methods sign and verify

Signed-off-by: ilyas585 <niyazov2023@gmail.com>

frostfs_api/cryptography/key_extension.py

@@ -0,0 +1,45 @@
+import base58
+import ecdsa
+from hashlib import sha256
+
+
+class KeyExtension:
+    def get_private_key_from_wif(self, wif: str) -> bytes:
+        """
+        Converts a WIF private key to a byte array.
+
+        :param wif: WIF private key in string format.
+        :return: Private key in byte format (32 bytes).
+        :raises ValueError: If the WIF key is incorrect.
+        """
+        assert not self.is_empty(wif)
+
+        decoded = base58.b58decode_check(wif)
+        if len(decoded) != 34 or decoded[0] != 0x80 or decoded[-1] != 0x01:
+            raise ValueError("Incorrect WIF private key")
+
+        private_key = decoded[1:-1]
+        return private_key
+
+    def get_public_key(self, private_key: bytes) -> bytes:
+        """
+        Extract public key from Private key
+
+        :param private_key: Private key in byte format (32 bytes).
+        :return: compressed public key in byte format (33 bytes).
+        :raises ValueError: If the private_key key is empty or null.
+        """
+        assert not self.is_empty(private_key)
+
+        if len(private_key) != 32:
+            raise ValueError(f"Incorrect len of private key, Expected: 32, Actual: {len(private_key)}")
+
+        public_key = ecdsa.SigningKey.from_string(private_key, curve=ecdsa.NIST256p).get_verifying_key()
+        compressed_public_key = public_key.to_string("compressed")
+        return compressed_public_key
+
+    @staticmethod
+    def is_empty(sequence_symbols: bytes | str):
+        if len(sequence_symbols) == 0 or sequence_symbols is None:
+            raise ValueError(f"Empty sequence symbols of key: {sequence_symbols}")
+        return False