From 882fb2f3c972e67303dd65873f05b8f3d58724e1 Mon Sep 17 00:00:00 2001 From: Chris O <46587501+ChrisO345@users.noreply.github.com> Date: Sun, 24 Sep 2023 20:36:06 +1300 Subject: [PATCH] Rewrite of base85.py algorithm (#9069) * rewrite of base85.py * changed maps to list comprehension * Apply suggestions from code review Co-authored-by: Tianyi Zheng --------- Co-authored-by: Tianyi Zheng --- ciphers/base85.py | 57 ++++++++++++++++++++++++++++++++++------------- 1 file changed, 41 insertions(+), 16 deletions(-) diff --git a/ciphers/base85.py b/ciphers/base85.py index afd1aff79..f0228e505 100644 --- a/ciphers/base85.py +++ b/ciphers/base85.py @@ -1,30 +1,55 @@ -import base64 +""" +Base85 (Ascii85) encoding and decoding + +https://en.wikipedia.org/wiki/Ascii85 +""" -def base85_encode(string: str) -> bytes: +def _base10_to_85(d: int) -> str: + return "".join(chr(d % 85 + 33)) + _base10_to_85(d // 85) if d > 0 else "" + + +def _base85_to_10(digits: list) -> int: + return sum(char * 85**i for i, char in enumerate(reversed(digits))) + + +def ascii85_encode(data: bytes) -> bytes: """ - >>> base85_encode("") + >>> ascii85_encode(b"") b'' - >>> base85_encode("12345") + >>> ascii85_encode(b"12345") b'0etOA2#' - >>> base85_encode("base 85") + >>> ascii85_encode(b"base 85") b'@UX=h+?24' """ - # encoded the input to a bytes-like object and then a85encode that - return base64.a85encode(string.encode("utf-8")) + binary_data = "".join(bin(ord(d))[2:].zfill(8) for d in data.decode("utf-8")) + null_values = (32 * ((len(binary_data) // 32) + 1) - len(binary_data)) // 8 + binary_data = binary_data.ljust(32 * ((len(binary_data) // 32) + 1), "0") + b85_chunks = [int(_s, 2) for _s in map("".join, zip(*[iter(binary_data)] * 32))] + result = "".join(_base10_to_85(chunk)[::-1] for chunk in b85_chunks) + return bytes(result[:-null_values] if null_values % 4 != 0 else result, "utf-8") -def base85_decode(a85encoded: bytes) -> str: +def ascii85_decode(data: bytes) -> bytes: """ - >>> base85_decode(b"") - '' - >>> base85_decode(b"0etOA2#") - '12345' - >>> base85_decode(b"@UX=h+?24") - 'base 85' + >>> ascii85_decode(b"") + b'' + >>> ascii85_decode(b"0etOA2#") + b'12345' + >>> ascii85_decode(b"@UX=h+?24") + b'base 85' """ - # a85decode the input into bytes and decode that into a human readable string - return base64.a85decode(a85encoded).decode("utf-8") + null_values = 5 * ((len(data) // 5) + 1) - len(data) + binary_data = data.decode("utf-8") + "u" * null_values + b85_chunks = map("".join, zip(*[iter(binary_data)] * 5)) + b85_segments = [[ord(_s) - 33 for _s in chunk] for chunk in b85_chunks] + results = [bin(_base85_to_10(chunk))[2::].zfill(32) for chunk in b85_segments] + char_chunks = [ + [chr(int(_s, 2)) for _s in map("".join, zip(*[iter(r)] * 8))] for r in results + ] + result = "".join("".join(char) for char in char_chunks) + offset = int(null_values % 5 == 0) + return bytes(result[: offset - null_values], "utf-8") if __name__ == "__main__":