IAS report signature verification

[sbellem]

From https://api.trustedservices.intel.com/documents/sgx-attestation-api-spec.pdf:

4.2.2 Report Signature

The Attestation Verification Report is cryptographically signed by Report Signing Key (owned by the Attestation Service) using the RSA-SHA256 algorithm. The signature is calculated over the entire body of the HTTP response. Base 64-encoded signature is then returned in a custom HTTP response header X-IASReport-Signature. To verify the signature over the report, you should the following steps:

1. Decode and verify the Report Signing Certificate Chain that was sent together with the report (see Report Signing Certificate Chain for details). Verify that the chain is rooted in a trusted Attestation Report Signing CA Certificate (available to download [from Development (DEV) attestation service portal] upon successful registration to IAS).
2. Optionally, verify that the certificates in the chain have not been revoked (using CRLs indicated in the certificates)
3. Verify the signature over the report using Attestation Report Signing Certificate.

4.2.3 Report Signing Certificate Chain

The public part of Report Key is distributed in the form of an x.509 digital certificate called Attestation Report Signing Certificate. It is a leaf certificate issued by the Attestation Report Signing CA Certificate:

1. Attestation Report Signing CA Certificate: CN=Intel SGX Attestation Report Signing CA, O=Intel Corporation, L=Santa Clara, ST=CA, C=US
2. Attestation Report Signing Certificate: CN=Intel SGX Attestation Report Signing, O=Intel Corporation, L=Santa Clara, ST=CA, C=US

A PEM-encoded certificate chain consisting of Attestation Report Signing Certificate and Attestation Report Signing CA Certificate is returned in a custom HTTP response header X-IASReport-Signing-Certificate.

The attestation report root CA certificate can be obtained at https://api.portal.trustedservices.intel.com/EPID-attestation. Look for the line:

Attestation Report Root CA Certificate: DER PEM

Implementation

See example (C++): https://github.com/hyperledger-labs/private-data-objects/blob/04d6b93737bc2c0446d292a028087ef4fb365ca7/common/crypto/verify_ias_report/verify-report.cpp

If using Python, some options are:

• https://www.pyopenssl.org/en/stable/api/crypto.html?highlight=X509_verify_cert#x509storecontext-objects
• https://github.com/wbond/certvalidator
• https://opendev.org/x/cursive/src/branch/master/cursive/certificate_utils.py