112 lines
3 KiB
Python
112 lines
3 KiB
Python
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import hashlib
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def sha256(x):
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""" Simple wrapper of hashlib sha256. """
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return hashlib.sha256(x).digest()
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def double_sha256(x):
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""" SHA-256 of SHA-256, as used extensively in bitcoin. """
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return sha256(sha256(x))
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class Base58Error(Exception):
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""" Exception used for Base58 errors. """
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_CHARS = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
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def _iter_encode(be_bytes: bytes):
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value = int.from_bytes(be_bytes, 'big')
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while value:
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value, mod = divmod(value, 58)
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yield _CHARS[mod]
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for byte in be_bytes:
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if byte != 0:
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break
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yield '1'
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def b58_encode(be_bytes: bytes):
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return ''.join(_iter_encode(be_bytes))[::-1]
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class Base58:
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""" Class providing base 58 functionality. """
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chars = '123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz'
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assert len(chars) == 58
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char_map = {c: n for n, c in enumerate(chars)}
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@classmethod
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def char_value(cls, c):
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val = cls.char_map.get(c)
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if val is None:
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raise Base58Error(f'invalid base 58 character "{c}"')
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return val
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@classmethod
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def decode(cls, txt):
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""" Decodes txt into a big-endian bytearray. """
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if isinstance(txt, memoryview):
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txt = str(txt)
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if isinstance(txt, bytes):
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txt = txt.decode()
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if not isinstance(txt, str):
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raise TypeError(f'a string is required, got {type(txt).__name__}')
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if not txt:
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raise Base58Error('string cannot be empty')
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value = 0
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for c in txt:
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value = value * 58 + cls.char_value(c)
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result = value.to_bytes((value.bit_length() + 7) // 8, 'big')
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# Prepend leading zero bytes if necessary
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count = 0
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for c in txt:
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if c != '1':
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break
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count += 1
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if count:
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result = bytes((0,)) * count + result
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return result
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@classmethod
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def _iter_encode(cls, be_bytes: bytes):
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value = int.from_bytes(be_bytes, 'big')
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while value:
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value, mod = divmod(value, 58)
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yield cls.chars[mod]
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for byte in be_bytes:
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if byte != 0:
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break
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yield '1'
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@classmethod
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def encode(cls, be_bytes):
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return ''.join(cls._iter_encode(be_bytes))[::-1]
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@classmethod
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def decode_check(cls, txt, hash_fn=double_sha256):
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""" Decodes a Base58Check-encoded string to a payload. The version prefixes it. """
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be_bytes = cls.decode(txt)
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result, check = be_bytes[:-4], be_bytes[-4:]
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if check != hash_fn(result)[:4]:
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raise Base58Error(f'invalid base 58 checksum for {txt}')
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return result
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@classmethod
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def encode_check(cls, payload, hash_fn=double_sha256):
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""" Encodes a payload bytearray (which includes the version byte(s))
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into a Base58Check string."""
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be_bytes = payload + hash_fn(payload)[:4]
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return b58_encode(be_bytes)
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