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scripts: fix compute_authenticode_hash for unsigned PEs #440

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scripts: fix compute_authenticode_hash for unsigned PEs #440

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15 changes: 11 additions & 4 deletions scripts/authenticode_transplant.py
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Original file line number Diff line number Diff line change
Expand Up @@ -447,10 +447,17 @@ def compute_authenticode_hash(pe_data: bytes, hash_algorithm: Optional[object] =
hash_data = (
pe_data[:checksum_offset] + pe_data[checksum_offset + 0x04 : certificate_table_offset]
)
hash_data += (
pe_data[certificate_table_offset + 0x08 : certificate_virtual_addr]
+ pe_data[certificate_virtual_addr + certificate_size :]
)
if certificate_virtual_addr == 0:
# Unsigned PE: the security data directory is empty (VirtualAddress == 0,
# Size == 0). The naive slice pe_data[0 + 0:] would re-append the entire
# file, producing a wrong digest. Instead, hash only the bytes that follow
# the 8-byte cert-dir data-directory entry.
hash_data += pe_data[certificate_table_offset + 0x08 :]
else:
hash_data += (
pe_data[certificate_table_offset + 0x08 : certificate_virtual_addr]
+ pe_data[certificate_virtual_addr + certificate_size :]
)

# Map cryptography hash algorithm to hashlib
if isinstance(hash_algorithm, crypto_hashes.SHA256):
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