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Fix ASN.1 issues in PKCS#7 and S/MIME signing (#10373) #10442

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Feb 21, 2024
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9 changes: 9 additions & 0 deletions CHANGELOG.rst
Original file line number Diff line number Diff line change
@@ -1,6 +1,15 @@
Changelog
=========

.. _v42-0-4:

42.0.4 - 2024-02-20
~~~~~~~~~~~~~~~~~~~

* Fixed ASN.1 encoding for PKCS7/SMIME signed messages. The fields ``SMIMECapabilities``
and ``SignatureAlgorithmIdentifier`` should now be correctly encoded according to the
definitions in :rfc:`2633` :rfc:`3370`.

.. _v42-0-3:

42.0.3 - 2024-02-15
Expand Down
28 changes: 24 additions & 4 deletions src/rust/src/pkcs7.rs
Original file line number Diff line number Diff line change
Expand Up @@ -104,9 +104,9 @@ fn sign_and_serialize<'p>(
// Subset of values OpenSSL provides:
// https://github.com/openssl/openssl/blob/667a8501f0b6e5705fd611d5bb3ca24848b07154/crypto/pkcs7/pk7_smime.c#L150
// removing all the ones that are bad cryptography
AES_256_CBC_OID,
AES_192_CBC_OID,
AES_128_CBC_OID,
&asn1::SequenceOfWriter::new([AES_256_CBC_OID]),
&asn1::SequenceOfWriter::new([AES_192_CBC_OID]),
&asn1::SequenceOfWriter::new([AES_128_CBC_OID]),
]))?;

let py_signers: Vec<(
Expand Down Expand Up @@ -205,7 +205,7 @@ fn sign_and_serialize<'p>(
},
digest_algorithm: digest_alg,
authenticated_attributes: authenticated_attrs,
digest_encryption_algorithm: x509::sign::compute_signature_algorithm(
digest_encryption_algorithm: compute_pkcs7_signature_algorithm(
py,
py_private_key,
py_hash_alg,
Expand Down Expand Up @@ -262,6 +262,26 @@ fn sign_and_serialize<'p>(
}
}

fn compute_pkcs7_signature_algorithm<'p>(
py: pyo3::Python<'p>,
private_key: &'p pyo3::PyAny,
hash_algorithm: &'p pyo3::PyAny,
rsa_padding: &'p pyo3::PyAny,
) -> pyo3::PyResult<common::AlgorithmIdentifier<'static>> {
let key_type = x509::sign::identify_key_type(py, private_key)?;
let has_pss_padding = rsa_padding.is_instance(types::PSS.get(py)?)?;
// For RSA signatures (with no PSS padding), the OID is always the same no matter the
// digest algorithm. See RFC 3370 (section 3.2).
if key_type == x509::sign::KeyType::Rsa && !has_pss_padding {
Ok(common::AlgorithmIdentifier {
oid: asn1::DefinedByMarker::marker(),
params: common::AlgorithmParameters::Rsa(Some(())),
})
} else {
x509::sign::compute_signature_algorithm(py, private_key, hash_algorithm, rsa_padding)
}
}

fn smime_canonicalize(data: &[u8], text_mode: bool) -> (Cow<'_, [u8]>, Cow<'_, [u8]>) {
let mut new_data_with_header = vec![];
let mut new_data_without_header = vec![];
Expand Down
5 changes: 4 additions & 1 deletion src/rust/src/x509/sign.rs
Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,10 @@ enum HashType {
Sha3_512,
}

fn identify_key_type(py: pyo3::Python<'_>, private_key: &pyo3::PyAny) -> pyo3::PyResult<KeyType> {
pub(crate) fn identify_key_type(
py: pyo3::Python<'_>,
private_key: &pyo3::PyAny,
) -> pyo3::PyResult<KeyType> {
if private_key.is_instance(types::RSA_PRIVATE_KEY.get(py)?)? {
Ok(KeyType::Rsa)
} else if private_key.is_instance(types::DSA_PRIVATE_KEY.get(py)?)? {
Expand Down
54 changes: 52 additions & 2 deletions tests/hazmat/primitives/test_pkcs7.py
Original file line number Diff line number Diff line change
Expand Up @@ -557,6 +557,50 @@ def test_sign_text(self, backend):
backend,
)

def test_smime_capabilities(self, backend):
data = b"hello world"
cert, key = _load_cert_key()
builder = (
pkcs7.PKCS7SignatureBuilder()
.set_data(data)
.add_signer(cert, key, hashes.SHA256())
)

sig_binary = builder.sign(serialization.Encoding.DER, [])

# 1.2.840.113549.1.9.15 (SMIMECapabilities) as an ASN.1 DER encoded OID
assert b"\x06\t*\x86H\x86\xf7\r\x01\t\x0f" in sig_binary

# 2.16.840.1.101.3.4.1.42 (aes256-CBC-PAD) as an ASN.1 DER encoded OID
aes256_cbc_pad_oid = b"\x06\x09\x60\x86\x48\x01\x65\x03\x04\x01\x2A"
# 2.16.840.1.101.3.4.1.22 (aes192-CBC-PAD) as an ASN.1 DER encoded OID
aes192_cbc_pad_oid = b"\x06\x09\x60\x86\x48\x01\x65\x03\x04\x01\x16"
# 2.16.840.1.101.3.4.1.2 (aes128-CBC-PAD) as an ASN.1 DER encoded OID
aes128_cbc_pad_oid = b"\x06\x09\x60\x86\x48\x01\x65\x03\x04\x01\x02"

# Each algorithm in SMIMECapabilities should be inside its own
# SEQUENCE.
# This is encoded as SEQUENCE_IDENTIFIER + LENGTH + ALGORITHM_OID.
# This tests that each algorithm is indeed encoded inside its own
# sequence. See RFC 2633, Appendix A for more details.
sequence_identifier = b"\x30"
for oid in [
aes256_cbc_pad_oid,
aes192_cbc_pad_oid,
aes128_cbc_pad_oid,
]:
len_oid = len(oid).to_bytes(length=1, byteorder="big")
assert sequence_identifier + len_oid + oid in sig_binary

_pkcs7_verify(
serialization.Encoding.DER,
sig_binary,
None,
[cert],
[],
backend,
)

def test_sign_no_capabilities(self, backend):
data = b"hello world"
cert, key = _load_cert_key()
Expand Down Expand Up @@ -677,9 +721,15 @@ def test_rsa_pkcs_padding_options(self, pad, backend):
sig.count(b"\x06\x09\x2a\x86\x48\x86\xf7\x0d\x01\x01\x08") == 1
)
else:
# This should be a pkcs1 sha512 signature
# This should be a pkcs1 RSA signature, which uses the
# `rsaEncryption` OID (1.2.840.113549.1.1.1) no matter which
# digest algorithm is used.
# See RFC 3370 section 3.2 for more details.
# This OID appears twice, once in the certificate itself and
# another in the SignerInfo data structure in the
# `digest_encryption_algorithm` field.
assert (
sig.count(b"\x06\x09\x2A\x86\x48\x86\xF7\x0D\x01\x01\x0D") == 1
sig.count(b"\x06\x09\x2A\x86\x48\x86\xF7\x0D\x01\x01\x01") == 2
)
_pkcs7_verify(
serialization.Encoding.DER,
Expand Down
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