[#2] Add methods sign and verify

frostfs_api/client/signer.py

@@ -0,0 +1,15 @@
+import ecdsa
+from hashlib import sha256
+
+
+class Signer:
+    def sign_rfc6979(self, private_key: bytes, message: bytes) -> bytes:
+        if len(private_key) == 0 or private_key is None:
+            raise ValueError(f"Incorrect private_key: {private_key}")
+
+        # SECP256k1 is the Bitcoin elliptic curve
+        sk = ecdsa.SigningKey.from_string(private_key, curve=ecdsa.SECP256k1, hashfunc=sha256)
+
+        signature = sk.sign(message, sigencode=ecdsa.util.sigencode_string)
+
+        return signature

frostfs_api/client/verifier.py

@@ -0,0 +1,18 @@
+import ecdsa
+from hashlib import sha256
+
+
+class Verifier:
+    def verify_rfc6979(self, public_key: bytes, message: bytes, signature: bytes) -> bool:
+        if len(public_key) == 0 or public_key is None:
+            raise ValueError(f"Incorrect public key: {public_key}")
+
+        if message is None or signature is None:
+            return False
+
+        vk = ecdsa.VerifyingKey.from_string(public_key, curve=ecdsa.SECP256k1, hashfunc=sha256)
+
+        try:
+            return vk.verify(signature, message)
+        except ecdsa.BadSignatureError:
+            return False

frostfs_api/crypto/key_extension.py

@@ -1,11 +1,21 @@
 import base58
+import ecdsa
 
 
 class KeyExtension:
-    def get_private_key_from_wif(self, wif: str):
+    def get_private_key_from_wif(self, wif: str) -> bytes:
+        if len(wif) == 0 or wif is None:
+            raise ValueError(f"Empty WIF private key: {wif}")
+
         decoded = base58.b58decode_check(wif)
         if len(decoded) != 34 or decoded[0] != 0x80 or decoded[-1] != 0x01:
-            raise ValueError("Incorrect WIF private key")
+            raise ValueError("Not decode WIF by base58")
 
         private_key = decoded[1:-1]
         return private_key
+
+    def get_public_key(self, private_key: bytes):
+        if len(private_key) == 0 or private_key is None:
+            raise ValueError(f"Empty private key: {private_key}")
+
+        return ecdsa.SigningKey.from_string(private_key, curve=ecdsa.SECP256k1).get_verifying_key().to_string()