verify JAR signature file using signature block file [WARNING: does not verify the actual file hashes!!!]

verify-jar-sf-with-sbf.py

#!/usr/bin/python3

import sys

from asn1crypto.x509 import Certificate as X509Cert
from cryptography.exceptions import InvalidSignature
from cryptography.hazmat.primitives.asymmetric.ec import ECDSA
from cryptography.hazmat.primitives.asymmetric.padding import PKCS1v15
from cryptography.hazmat.primitives.hashes import SHA1, SHA224, SHA256, SHA384, SHA512
from cryptography.hazmat.primitives.serialization import Encoding
from cryptography.hazmat.primitives.serialization.pkcs7 import load_der_pkcs7_certificates
from pyasn1.codec.der.decoder import decode as pyasn1_decode
from pyasn1_modules import rfc5480

HASHERS = {
    rfc5480.id_sha1: SHA1,
    rfc5480.id_sha224: SHA224,
    rfc5480.id_sha256: SHA256,
    rfc5480.id_sha384: SHA384,
    rfc5480.id_sha512: SHA512,
}

for key in sys.argv[1:]:
    print(key)
    with open(key.rsplit(".", 1)[0] + ".SF", "rb") as fh:
        sf = fh.read()
    with open(key, "rb") as fh:
        sbf = fh.read()
    asn = pyasn1_decode(sbf)
    sig = asn[0][-1][-1][-1][-1].asOctets()
    hsh = asn[0][-1][-1][-1][-3][0]
    alg = HASHERS[hsh]
    if alg is SHA1:
        print("WARNING: SHA1")
    for cert in load_der_pkcs7_certificates(sbf):
        c = X509Cert.load(cert.public_bytes(Encoding.DER))
        print(c.subject.human_friendly)
        pk = cert.public_key()
        try:
            if key.endswith("RSA"):
                pk.verify(sig, sf, PKCS1v15(), alg())
            elif key.endswith("EC"):
                pk.verify(sig, sf, ECDSA(alg()))
            else:
                pk.verify(sig, sf, alg())
        except InvalidSignature:
            print("FAILED")
        else:
            print("OK")
        print()