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Corrected SPDM signed measurement verification for newer versions that include a context prefix #216

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Merged
mraineri merged 1 commit into from
Jun 12, 2026
Merged

Corrected SPDM signed measurement verification for newer versions that include a context prefix #216

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48 changes: 35 additions & 13 deletions redfish_utilities/component_integrity.py
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Original file line number Diff line number Diff line change
Expand Up @@ -268,6 +268,7 @@ def parse_signed_measurements(response, action_context):
(
measurements["VCA"],
measurements["Measurements"],
measurements["SPDMPrefix"],
measurements["MeasurementLog"],
measurements["Signature"],
measurements["RequestNonce"],
Expand Down Expand Up @@ -304,13 +305,13 @@ def print_signed_measurements(parsed_measurements):
print(" Supported Versions: {}".format(", ".join(parsed_measurements["VCA"]["SupportedVersions"])))
print(
" Requester Size Limits: Max Transfer Size: {}, Max Message Size: {}".format(
parsed_measurements["VCA"]["RequesterMaxMessageSize"],
parsed_measurements["VCA"]["RequesterMaxTransferSize"],
parsed_measurements["VCA"]["RequesterMaxMessageSize"],
)
)
print(
" Responder Size Limits: Max Transfer Size: {}, Max Message Size: {}".format(
parsed_measurements["VCA"]["ResponderMaxMessageSize"],
parsed_measurements["VCA"]["ResponderMaxTransferSize"],
parsed_measurements["VCA"]["ResponderMaxMessageSize"],
)
)
Expand Down Expand Up @@ -408,28 +409,36 @@ def verify_signed_measurements(context, parsed_measurements):
)
try:
# Verification is dependent on the key type
if parsed_measurements["SPDMPrefix"]:
# Newer versions hash the measurement data and attach a prefix
measurement_log_hash = hashes.Hash(hash_algorithm)
measurement_log_hash.update(parsed_measurements["MeasurementLog"])
full_measurement_log = parsed_measurements["SPDMPrefix"] + measurement_log_hash.finalize()
else:
# Older versions of SPDM don't have a prefix
full_measurement_log = parsed_measurements["MeasurementLog"]
if isinstance(public_key, ec.EllipticCurvePublicKey):
# ECDSA signatures require breaking down the signature in to a DER-encoded format
# It also requires the hash algorithm to be provided
sig_half = int(len(parsed_measurements["Signature"]) / 2)
r = int.from_bytes(parsed_measurements["Signature"][:sig_half], byteorder="big")
s = int.from_bytes(parsed_measurements["Signature"][sig_half:], byteorder="big")
public_key.verify(
utils.encode_dss_signature(r, s), parsed_measurements["MeasurementLog"], ec.ECDSA(hash_algorithm)
utils.encode_dss_signature(r, s), full_measurement_log, ec.ECDSA(hash_algorithm)
)
elif isinstance(public_key, rsa.RSAPublicKey):
# RSA signatures require the padding and hash algorithm to be provided
public_key.verify(
parsed_measurements["Signature"],
parsed_measurements["MeasurementLog"],
full_measurement_log,
padding.PKCS1v15(),
hash_algorithm,
)
else:
# Other key types don't require additional info
# The cryptography module uses this for the following key types: Ed448, Ed25519, and ML-DSA
# SLH-DSA is currently not supported, but anticipating the same pattern will be used when it's added
public_key.verify(parsed_measurements["Signature"], parsed_measurements["MeasurementLog"])
public_key.verify(parsed_measurements["Signature"], full_measurement_log)
except Exception:
raise RedfishInvalidSignedMeasurements("Failed to verify the signature with the public key")
else:
Expand All @@ -449,6 +458,7 @@ def _parse_spdm_signed_measurements(version, signing_algorithm, raw_measurements
Returns:
A dictionary of the VCA transcript; None if the SPDM version is less than 1.2
A list of dictionaries containing the measurements
A byte array containing the SPDM prefix
A byte array containing the measurement log data
A byte array containing the signature of the measurement log data
A byte array containing the request nonce
Expand All @@ -463,7 +473,9 @@ def _parse_spdm_signed_measurements(version, signing_algorithm, raw_measurements
# Parse the SPDM version
try:
# Wanted to keep the version parsing/comparison simple without bringing in packaging or other dependencies
version_num = int(version.split(".")[0]) * 100 + int(version.split(".")[1])
major = int(version.split(".")[0])
minor = int(version.split(".")[1])
version_num = major * 100 + minor
except Exception:
raise RedfishInvalidSignedMeasurements("Invalid SPDM version: {}".format(version))

Expand All @@ -472,6 +484,7 @@ def _parse_spdm_signed_measurements(version, signing_algorithm, raw_measurements
measurements = []
request_nonce = None
signature_found = False
spdm_prefix = None

# Separate the signature from the measurement data
try:
Expand Down Expand Up @@ -513,7 +526,16 @@ def _parse_spdm_signed_measurements(version, signing_algorithm, raw_measurements
if not signature_found:
raise RedfishInvalidSignedMeasurements("No signature found in SPDM messages")

return vca, measurements, measurement_log, signature, request_nonce
# SPDM 1.2+ includes an "SPDM prefix" that needs to be included in the signature verification
if version_num >= 102:
spdm_prefix_version = "dmtf-spdm-v{}.{}.*".format(major, minor).encode("utf-8")
spdm_prefix_context = "responder-measurements signing".encode("utf-8")
spdm_prefix = spdm_prefix_version + spdm_prefix_version + spdm_prefix_version + spdm_prefix_version
while len(spdm_prefix) < (100 - len(spdm_prefix_context)):
spdm_prefix += b"\x00"
spdm_prefix = spdm_prefix + spdm_prefix_context

return vca, measurements, spdm_prefix, measurement_log, signature, request_nonce


def _spdm_parse_version_req_resp(data, offset, vca):
Expand Down Expand Up @@ -547,9 +569,9 @@ def _spdm_parse_version_req_resp(data, offset, vca):
# Extract the supported SPDM versions; ignore the "Alpha" version
for i in range(num_versions):
version = "{}.{}.{}".format(
(data[offset + 6 + 2 * i] >> 4) & 0xF,
data[offset + 6 + 2 * i] & 0xF,
(data[offset + 7 + 2 * i] >> 4) & 0xF,
data[offset + 7 + 2 * i] & 0xF,
(data[offset + 6 + 2 * i] >> 4) & 0xF,
)
vca["SupportedVersions"].append(version)
offset += response_length
Expand All @@ -572,9 +594,9 @@ def _spdm_parse_capabilities_req_resp(data, offset, version_num, vca):
"""

vca["RequesterMaxTransferSize"] = None
vca["RequesterMaxSPDMMessageSize"] = None
vca["RequesterMaxMessageSize"] = None
vca["ResponderMaxTransferSize"] = None
vca["ResponderMaxSPDMMessageSize"] = None
vca["ResponderMaxMessageSize"] = None

# GET_CAPABILITIES request
# Check the request code is correct
Expand All @@ -589,7 +611,7 @@ def _spdm_parse_capabilities_req_resp(data, offset, version_num, vca):
else:
# SPDM 1.2+ has a transfer size fields
vca["RequesterMaxTransferSize"] = int.from_bytes(data[offset + 12 : offset + 16], byteorder="little")
vca["RequesterMaxSPDMMessageSize"] = int.from_bytes(data[offset + 16 : offset + 20], byteorder="little")
vca["RequesterMaxMessageSize"] = int.from_bytes(data[offset + 16 : offset + 20], byteorder="little")
offset += 20

# CAPABILITIES response
Expand All @@ -601,7 +623,7 @@ def _spdm_parse_capabilities_req_resp(data, offset, version_num, vca):
else:
# SPDM 1.2+ has a transfer size fields
vca["ResponderMaxTransferSize"] = int.from_bytes(data[offset + 12 : offset + 16], byteorder="little")
vca["ResponderMaxSPDMMessageSize"] = int.from_bytes(data[offset + 16 : offset + 20], byteorder="little")
vca["ResponderMaxMessageSize"] = int.from_bytes(data[offset + 16 : offset + 20], byteorder="little")
alg_length = 0
if version_num >= 103:
# SPDM 1.3+ has an optional "supported algorithms" field
Expand Down
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