126 lines
5.4 KiB
Python
126 lines
5.4 KiB
Python
"""Export public APK signing information and verify continuity. No private keys."""
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import argparse
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import hashlib
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import json
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import struct
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import zipfile
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from pathlib import Path
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from cryptography.hazmat.primitives import serialization
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from cryptography.hazmat.primitives.serialization import pkcs7
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from cryptography import x509
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def length_prefixed(data, offset=0):
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size = struct.unpack_from('<I', data, offset)[0]
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end = offset + 4 + size
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if end > len(data):
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raise ValueError('Malformed APK signing record.')
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return data[offset + 4:end], end
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def modern_certificate(apk):
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# APK v2/v3 certificates live before the ZIP central directory, not META-INF.
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with open(apk, 'rb') as stream:
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stream.seek(0, 2)
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size = stream.tell()
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stream.seek(max(0, size - 65557))
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tail = stream.read()
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eocd = tail.rfind(b'PK\x05\x06')
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if eocd < 0:
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raise ValueError('Missing ZIP directory.')
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central = struct.unpack_from('<I', tail, eocd + 16)[0]
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stream.seek(central - 24)
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footer = stream.read(24)
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if footer[8:] != b'APK Sig Block 42':
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return None
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block_size = struct.unpack_from('<Q', footer)[0]
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if block_size < 24 or block_size + 8 > central:
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raise ValueError('Malformed APK signing block.')
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stream.seek(central - block_size - 8)
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block = stream.read(block_size + 8)
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if struct.unpack_from('<Q', block)[0] != block_size:
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raise ValueError('APK signing block sizes differ.')
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offset = 8
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while offset < len(block) - 24:
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pair_size = struct.unpack_from('<Q', block, offset)[0]
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offset += 8
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pair = block[offset:offset + pair_size]
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if pair_size < 4 or len(pair) != pair_size:
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raise ValueError('Malformed APK signer pair.')
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scheme = struct.unpack_from('<I', pair)[0]
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if scheme in (0x7109871A, 0xF05368C0, 0x1B93AD61):
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signers, _ = length_prefixed(pair[4:])
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signer, signer_end = length_prefixed(signers)
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if signer_end != len(signers):
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raise ValueError('Multiple APK signers are not supported by this report.')
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signed_data, _ = length_prefixed(signer)
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_, digest_end = length_prefixed(signed_data)
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certificates, _ = length_prefixed(signed_data, digest_end)
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cert_der, _ = length_prefixed(certificates)
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return x509.load_der_x509_certificate(cert_der)
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offset += pair_size
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return None
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def certificate(apk):
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modern = modern_certificate(apk)
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if modern is not None:
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return modern
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with zipfile.ZipFile(apk) as archive:
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blocks = [name for name in archive.namelist()
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if name.upper().startswith('META-INF/')
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and name.upper().endswith(('.RSA', '.EC', '.DSA'))]
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if len(blocks) != 1:
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raise ValueError('Expected one v1 signing certificate block; verify APK with apksigner.')
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certificates = pkcs7.load_der_pkcs7_certificates(archive.read(blocks[0]))
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if len(certificates) != 1:
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raise ValueError('Expected one signing certificate, not a certificate chain.')
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return certificates[0]
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def main():
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parser = argparse.ArgumentParser()
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parser.add_argument('--previous', required=True)
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parser.add_argument('--current', required=True)
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parser.add_argument('--output-dir', required=True)
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args = parser.parse_args()
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previous = certificate(args.previous)
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current = certificate(args.current)
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old_der = previous.public_bytes(serialization.Encoding.DER)
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der = current.public_bytes(serialization.Encoding.DER)
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public = current.public_key().public_bytes(
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serialization.Encoding.DER, serialization.PublicFormat.SubjectPublicKeyInfo)
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if old_der != der:
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raise ValueError('Signing certificate changed. Existing signing material must be preserved.')
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output = Path(args.output_dir)
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output.mkdir(parents=True, exist_ok=True)
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details = {
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'appName': 'TPSchedule',
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'applicationId': 'com.tpschedule.app',
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'certificateUnchanged': True,
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'subject': current.subject.rfc4514_string(),
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'certificateSHA256': hashlib.sha256(der).hexdigest().upper(),
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'certificateSHA1': hashlib.sha1(der).hexdigest().upper(),
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'certificateMD5': hashlib.md5(der).hexdigest().upper(),
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'publicKeySHA256': hashlib.sha256(public).hexdigest().upper(),
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'publicKeyMD5': hashlib.md5(public).hexdigest().upper(),
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'publicKeySPKIHex': public.hex().upper(),
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'publicKeyBits': current.public_key().key_size,
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'certificateNote': 'Existing Android Debug certificate preserved; store/filing acceptance must be checked.',
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}
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(output / 'TPSchedule-signing-info.json').write_text(
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json.dumps(details, ensure_ascii=False, indent=2), encoding='utf-8')
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(output / 'TPSchedule-signing-certificate.pem').write_bytes(
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current.public_bytes(serialization.Encoding.PEM))
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(output / 'TPSchedule-public-key.pem').write_bytes(
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current.public_key().public_bytes(serialization.Encoding.PEM,
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serialization.PublicFormat.SubjectPublicKeyInfo))
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print(json.dumps({'certificateUnchanged': True,
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'certificateSHA256': details['certificateSHA256'],
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'publicFiles': str(output)}, ensure_ascii=True))
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if __name__ == '__main__':
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main()
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