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Add keyUsage digitalSignature validation for signer certificate #477

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Add keyUsage digitalSignature validation for signer certificate #477

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e0b3a17
Add keyUsage digitalSignature validation for signer certificate
olszomal Dec 16, 2025
074ec47
tests: add digitalSignature keyUsage to leaf certificate
olszomal Dec 16, 2025
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12 changes: 10 additions & 2 deletions osslsigncode.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2535,9 +2535,17 @@ static int verify_authenticode(FILE_FORMAT_CTX *ctx, PKCS7 *p7, time_t time, X50
if (!crlok)
goto out;
}
/* check extended key usage flag XKU_CODE_SIGN */
/*
* Verify that:
* - extendedKeyUsage, if present, permits codeSigning (RFC 5280 section 4.2.1.12)
* - keyUsage, if present, permits digitalSignature (RFC 5280 section 4.2.1.3)
*/
if (!(X509_get_extended_key_usage(signer) & XKU_CODE_SIGN)) {
fprintf(stderr, "Unsupported Signer's certificate purpose XKU_CODE_SIGN\n");
fprintf(stderr, "Signer certificate rejected: extendedKeyUsage does not permit codeSigning\n");
goto out;
}
if (!(X509_get_key_usage(signer) & X509v3_KU_DIGITAL_SIGNATURE)) {
fprintf(stderr, "Signer certificate rejected: keyUsage does not permit digitalSignature\n");
goto out;
}

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12 changes: 12 additions & 0 deletions tests/make_certificates.py
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Original file line number Diff line number Diff line change
Expand Up @@ -338,6 +338,17 @@ def make_cert(self, public_key, not_before, days) -> Certificate:
authority_key = AuthorityKeyIdentifier.from_issuer_subject_key_identifier(
self.issuer_cert.extensions.get_extension_for_class(SubjectKeyIdentifier).value
)
key_usage = KeyUsage(
digital_signature=True,
content_commitment=False,
key_encipherment=False,
data_encipherment=False,
key_agreement=False,
key_cert_sign=False,
crl_sign=False,
encipher_only=False,
decipher_only=False
)
extended_key_usage = ExtendedKeyUsage(
[ExtendedKeyUsageOID.CODE_SIGNING]
)
Expand All @@ -352,6 +363,7 @@ def make_cert(self, public_key, not_before, days) -> Certificate:
.add_extension(BasicConstraints(ca=False, path_length=None), critical=False)
.add_extension(SubjectKeyIdentifier.from_public_key(public_key), critical=False)
.add_extension(authority_key, critical=False)
.add_extension(key_usage, critical=False)
.add_extension(extended_key_usage, critical=False)
.add_extension(self.create_x509_crldp(), critical=False)
.sign(self.issuer_key, SHA256())
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