mylesmarkevich/ops-xld_logchecker.py
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Added some more comments describing the algorithm

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puddly
2018-08-05 18:25:39 -04:00
parent 3ec6f762c3
commit 63b088915b
1 changed files with 20 additions and 21 deletions
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xld.py
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@@ -16,10 +16,11 @@ def rotate_right(n, k):
def sha256(data, initial_state):
# Non-standard initial state
state = initial_state
# Standard round constants
round_constants = (0x428A2F98, 0x71374491, 0xB5C0FBCF, 0xE9B5DBA5, 0x3956C25B, 0x59F111F1, 0x923F82A4, 0xAB1C5ED5, 0xD807AA98, 0x12835B01, 0x243185BE, 0x550C7DC3, 0x72BE5D74, 0x80DEB1FE, 0x9BDC06A7, 0xC19BF174, 0xE49B69C1, 0xEFBE4786, 0x0FC19DC6, 0x240CA1CC, 0x2DE92C6F, 0x4A7484AA, 0x5CB0A9DC, 0x76F988DA, 0x983E5152, 0xA831C66D, 0xB00327C8, 0xBF597FC7, 0xC6E00BF3, 0xD5A79147, 0x06CA6351, 0x14292967, 0x27B70A85, 0x2E1B2138, 0x4D2C6DFC, 0x53380D13, 0x650A7354, 0x766A0ABB, 0x81C2C92E, 0x92722C85, 0xA2BFE8A1, 0xA81A664B, 0xC24B8B70, 0xC76C51A3, 0xD192E819, 0xD6990624, 0xF40E3585, 0x106AA070, 0x19A4C116, 0x1E376C08, 0x2748774C, 0x34B0BCB5, 0x391C0CB3, 0x4ED8AA4A, 0x5B9CCA4F, 0x682E6FF3, 0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208, 0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2)
ROUND_CONSTANTS = (0x428A2F98, 0x71374491, 0xB5C0FBCF, 0xE9B5DBA5, 0x3956C25B, 0x59F111F1, 0x923F82A4, 0xAB1C5ED5, 0xD807AA98, 0x12835B01, 0x243185BE, 0x550C7DC3, 0x72BE5D74, 0x80DEB1FE, 0x9BDC06A7, 0xC19BF174, 0xE49B69C1, 0xEFBE4786, 0x0FC19DC6, 0x240CA1CC, 0x2DE92C6F, 0x4A7484AA, 0x5CB0A9DC, 0x76F988DA, 0x983E5152, 0xA831C66D, 0xB00327C8, 0xBF597FC7, 0xC6E00BF3, 0xD5A79147, 0x06CA6351, 0x14292967, 0x27B70A85, 0x2E1B2138, 0x4D2C6DFC, 0x53380D13, 0x650A7354, 0x766A0ABB, 0x81C2C92E, 0x92722C85, 0xA2BFE8A1, 0xA81A664B, 0xC24B8B70, 0xC76C51A3, 0xD192E819, 0xD6990624, 0xF40E3585, 0x106AA070, 0x19A4C116, 0x1E376C08, 0x2748774C, 0x34B0BCB5, 0x391C0CB3, 0x4ED8AA4A, 0x5B9CCA4F, 0x682E6FF3, 0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208, 0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2)
# Pad the data with a single 1 bit, enough zeroes, and the original message bit length
L = 8 * len(data)
@@ -30,17 +31,14 @@ def sha256(data, initial_state):
for start in range(0, len(data), 64):
# Process chunks of 64 bytes
chunk = data[start:start + 64]
round_state = [0] * 64
for i in range(0, len(chunk), 4):
round_state[i // 4] = int.from_bytes(chunk[i:i + 4], 'big')
round_state = 4 * [int.from_bytes(chunk[i:i + 4], 'big') for i in range(0, len(chunk), 4)]
for i in range(16, 64):
s0 = rotate_right(round_state[i - 15], 7) ^ rotate_right(round_state[i - 15], 18) ^ (round_state[i - 15] >> 3)
s1 = rotate_right(round_state[i - 2], 17) ^ rotate_right(round_state[i - 2], 19) ^ (round_state[i - 2] >> 10)
round_state[i] = (round_state[i - 16] + s0 + round_state[i - 7] + s1) & 0xFFFFFFFF
a, b, c, d, e, f, g, h = state
for i in range(64):
@@ -50,7 +48,7 @@ def sha256(data, initial_state):
s1 = rotate_right(e, 6) ^ rotate_right(e, 11) ^ rotate_right(e, 25)
ch = (e & f) ^ ((~e) & g)
t1 = h + s1 + ch + round_constants[i] + round_state[i]
t1 = h + s1 + ch + ROUND_CONSTANTS[i] + round_state[i]
h = g
g = f
@@ -67,7 +65,7 @@ def sha256(data, initial_state):
def scramble(data):
MAGIC_CONSTANTS = [0x99036946, 0xe99db8e7, 0xe3ae2fa7, 0xa339740, 0xf06eb6a9, 0x92ff9b65, 0x28f7873, 0x9070e316]
MAGIC_CONSTANTS = [0x99036946, 0xE99DB8E7, 0xE3AE2FA7, 0xA339740, 0xF06EB6A9, 0x92FF9B65, 0x28F7873, 0x9070E316]
# Split off the unaligned part
unpadded_chunk = b''
@@ -82,8 +80,8 @@ def scramble(data):
output = []
# Magic initial state
X = 0x6479b873
Y = 0x48853afc
X = 0x6479B873
Y = 0x48853AFC
for offset in range(0, len(data), 8):
# Read off two 32-bit integers
@@ -127,15 +125,11 @@ def scramble(data):
return b''.join(output)
def encode(data):
def nonstandard_base64_encode(data, alphabet):
# Non-standard base64 alphabet
mapping = str.maketrans(
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/',
'0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz._'
)
mapping = str.maketrans('ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/', alphabet)
# Output has no padding bytes
return base64.b64encode(data).decode('ascii').translate(mapping).rstrip('=')
return base64.b64encode(data).decode('ascii').translate(mapping)
def extract_info(data):
@@ -158,11 +152,16 @@ def extract_info(data):
def xld_verify(data):
data, version, old_signature = extract_info(data)
initial_state = (0x1D95E3A4, 0x06520EF5, 0x3A9CFB75, 0x6104BCAE, 0x09CEDA82, 0xBA55E60B, 0xEAEC16C6, 0xEB19AF15)
hashed_data = (sha256(data.encode('utf-8'), initial_state) + '\nVersion=0001').encode('ascii')
INITIAL_STATE = (0x1D95E3A4, 0x06520EF5, 0x3A9CFB75, 0x6104BCAE, 0x09CEDA82, 0xBA55E60B, 0xEAEC16C6, 0xEB19AF15)
scrambled_data = scramble(hashed_data)
signature = encode(scrambled_data)
# SHA256 with a different initial state
checksum = sha256(data.encode('utf-8'), INITIAL_STATE).encode('ascii')
# A fixed version string is appended to the the hex digest of the log text
scrambled = scramble(checksum + b'\nVersion=0001')
# No padding bytes
signature = nonstandard_base64_encode(scrambled, '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz._').rstrip('=')
return data, version, old_signature, signature