add from npub to publickey (#22)

nostr/key.py

@@ -21,6 +21,14 @@ class PublicKey:
         pk = secp256k1.PublicKey(b"\x02" + self.raw_bytes, True)
         return pk.schnorr_verify(bytes.fromhex(hash), bytes.fromhex(sig), None, True)
 
+    @classmethod
+    def from_npub(cls, npub: str):
+        """ Load a PublicKey from its bech32/npub form """
+        hrp, data, spec = bech32.bech32_decode(npub)
+        raw_public_key = bech32.convertbits(data, 5, 8)[:-1]
+        return cls(bytes(raw_public_key))
+
+
 class PrivateKey:
     def __init__(self, raw_secret: bytes=None) -> None:
         if not raw_secret is None:
@@ -85,7 +93,7 @@ class PrivateKey:
         sk = secp256k1.PrivateKey(self.raw_secret)
         sig = sk.schnorr_sign(hash, None, raw=True)
         return sig.hex()
-    
+
     def __eq__(self, other):
         return self.raw_secret == other.raw_secret
 
@@ -94,4 +102,4 @@ ffi = FFI()
 @ffi.callback("int (unsigned char *, const unsigned char *, const unsigned char *, void *)")
 def copy_x(output, x32, y32, data):
     ffi.memmove(output, x32, 32)
-    return 1
+    return 1