add bech32 key encoding

Author: jeffthibault

nostr/bech32.py

@@ -0,0 +1,137 @@
+# Copyright (c) 2017, 2020 Pieter Wuille
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+
+"""Reference implementation for Bech32/Bech32m and segwit addresses."""
+
+
+from enum import Enum
+
+class Encoding(Enum):
+    """Enumeration type to list the various supported encodings."""
+    BECH32 = 1
+    BECH32M = 2
+
+CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
+BECH32M_CONST = 0x2bc830a3
+
+def bech32_polymod(values):
+    """Internal function that computes the Bech32 checksum."""
+    generator = [0x3b6a57b2, 0x26508e6d, 0x1ea119fa, 0x3d4233dd, 0x2a1462b3]
+    chk = 1
+    for value in values:
+        top = chk >> 25
+        chk = (chk & 0x1ffffff) << 5 ^ value
+        for i in range(5):
+            chk ^= generator[i] if ((top >> i) & 1) else 0
+    return chk
+
+
+def bech32_hrp_expand(hrp):
+    """Expand the HRP into values for checksum computation."""
+    return [ord(x) >> 5 for x in hrp] + [0] + [ord(x) & 31 for x in hrp]
+
+
+def bech32_verify_checksum(hrp, data):
+    """Verify a checksum given HRP and converted data characters."""
+    const = bech32_polymod(bech32_hrp_expand(hrp) + data)
+    if const == 1:
+        return Encoding.BECH32
+    if const == BECH32M_CONST:
+        return Encoding.BECH32M
+    return None
+
+def bech32_create_checksum(hrp, data, spec):
+    """Compute the checksum values given HRP and data."""
+    values = bech32_hrp_expand(hrp) + data
+    const = BECH32M_CONST if spec == Encoding.BECH32M else 1
+    polymod = bech32_polymod(values + [0, 0, 0, 0, 0, 0]) ^ const
+    return [(polymod >> 5 * (5 - i)) & 31 for i in range(6)]
+
+
+def bech32_encode(hrp, data, spec):
+    """Compute a Bech32 string given HRP and data values."""
+    combined = data + bech32_create_checksum(hrp, data, spec)
+    return hrp + '1' + ''.join([CHARSET[d] for d in combined])
+
+def bech32_decode(bech):
+    """Validate a Bech32/Bech32m string, and determine HRP and data."""
+    if ((any(ord(x) < 33 or ord(x) > 126 for x in bech)) or
+            (bech.lower() != bech and bech.upper() != bech)):
+        return (None, None, None)
+    bech = bech.lower()
+    pos = bech.rfind('1')
+    if pos < 1 or pos + 7 > len(bech) or len(bech) > 90:
+        return (None, None, None)
+    if not all(x in CHARSET for x in bech[pos+1:]):
+        return (None, None, None)
+    hrp = bech[:pos]
+    data = [CHARSET.find(x) for x in bech[pos+1:]]
+    spec = bech32_verify_checksum(hrp, data)
+    if spec is None:
+        return (None, None, None)
+    return (hrp, data[:-6], spec)
+
+def convertbits(data, frombits, tobits, pad=True):
+    """General power-of-2 base conversion."""
+    acc = 0
+    bits = 0
+    ret = []
+    maxv = (1 << tobits) - 1
+    max_acc = (1 << (frombits + tobits - 1)) - 1
+    for value in data:
+        if value < 0 or (value >> frombits):
+            return None
+        acc = ((acc << frombits) | value) & max_acc
+        bits += frombits
+        while bits >= tobits:
+            bits -= tobits
+            ret.append((acc >> bits) & maxv)
+    if pad:
+        if bits:
+            ret.append((acc << (tobits - bits)) & maxv)
+    elif bits >= frombits or ((acc << (tobits - bits)) & maxv):
+        return None
+    return ret
+
+
+def decode(hrp, addr):
+    """Decode a segwit address."""
+    hrpgot, data, spec = bech32_decode(addr)
+    if hrpgot != hrp:
+        return (None, None)
+    decoded = convertbits(data[1:], 5, 8, False)
+    if decoded is None or len(decoded) < 2 or len(decoded) > 40:
+        return (None, None)
+    if data[0] > 16:
+        return (None, None)
+    if data[0] == 0 and len(decoded) != 20 and len(decoded) != 32:
+        return (None, None)
+    if data[0] == 0 and spec != Encoding.BECH32 or data[0] != 0 and spec != Encoding.BECH32M:
+        return (None, None)
+    return (data[0], decoded)
+
+
+def encode(hrp, witver, witprog):
+    """Encode a segwit address."""
+    spec = Encoding.BECH32 if witver == 0 else Encoding.BECH32M
+    ret = bech32_encode(hrp, [witver] + convertbits(witprog, 8, 5), spec)
+    if decode(hrp, ret) == (None, None):
+        return None
+    return ret

nostr/key.py

@@ -4,6 +4,7 @@
 from secp256k1 import PrivateKey, PublicKey
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
 from cryptography.hazmat.primitives import padding
+from . import bech32
 
 def generate_private_key() -> str:
     private_key = PrivateKey()
@@ -23,6 +24,22 @@ def get_key_pair() -> tuple:
     public_key = private_key.pubkey.serialize().hex()
     return (private_key.serialize(), public_key[2:])
 
+def bech32_encode_private_key(private_key: str) -> str:
+    converted_bits = bech32.convertbits(bytes.fromhex(private_key), 8, 5)
+    return bech32.bech32_encode("nsec", converted_bits, bech32.Encoding.BECH32)
+
+def bech32_decode_private_key(private_key_bech32: str) -> str:
+    data = bech32.bech32_decode(private_key_bech32)[1]
+    return bytes(bech32.convertbits(data, 5, 8, False)).hex()
+
+def bech32_encode_public_key(public_key: str) -> str:
+    converted_bits = bech32.convertbits(bytes.fromhex(public_key), 8, 5)
+    return bech32.bech32_encode("npub", converted_bits, bech32.Encoding.BECH32)
+
+def bech32_decode_public_key(public_key_bech32: str) -> str:
+    data = bech32.bech32_decode(public_key_bech32)[1]
+    return bytes(bech32.convertbits(data, 5, 8, False)).hex()
+
 def tweak_add_private_key(private_key: str, scalar: bytes) -> str:
     sk = PrivateKey(bytes.fromhex(private_key))
     tweaked_secret = sk.tweak_add(scalar)