I was implementing secret provisioning on top of the remote attestation code provided. I have found the following issues in the code:
You are attempting to sign a SHA-256 digest with a 128-bit RSA key in the quoting enclave. RSA cannot be used to sign data larger in size than the key. Fixing this would involve either using SHA-1 (not recommended) or using larger RSA keys.
As per the Intel SGX spec, the signature is stored in place of the mac in the report structure. However, you declared that as a 16-byte buffer this is smaller in size than 256-bits required for the signature (assuming an RSA key of 256-bits). I fixed this by utilizing a second structure that I called quote_t because I found a few instances where the size of report_t is hard coded . This also allowed me to specify a larger signature size that can be used with an RSA-2048 key. Bear in mind that RSA-128 is trivial to break.
The calls being made to rsa_sign and rsa_verify specify data_len = 0 which is only allowed when you define the type of the md used as input to the function. However, you are not doing so and as a result the signature is being generated over a buffer of size 0 and verified over a buffer of size 0. If you check polarSSL's source code, this returns success without carrying out any computation. I would suggest defining the type of message digest instead of using the arbitrary_data flag.
Finally, this is more of a gripe I have with your implementation than an actual issue, however, the quoting enclave, according to Intel's spec, has a known public key. This indicates that the keys in use are not ephemeral. However, you are generating RSA keys on every execution of the attestation process. I may have missed something while reading the spec, but if not, I think that utilizing a pre-computed key will make the attestation execute faster on QEMU and also adhere more to the original spec.
N.B.: I can generate a pull request if you wish with the modifications I outlined but it will contain the provisioning code as it is intermingled in the remote attestation process.
I was implementing secret provisioning on top of the remote attestation code provided. I have found the following issues in the code:
quote_tbecause I found a few instances where the size ofreport_tis hard coded . This also allowed me to specify a larger signature size that can be used with an RSA-2048 key. Bear in mind that RSA-128 is trivial to break.rsa_signandrsa_verifyspecifydata_len = 0which is only allowed when you define the type of the md used as input to the function. However, you are not doing so and as a result the signature is being generated over a buffer of size 0 and verified over a buffer of size 0. If you check polarSSL's source code, this returns success without carrying out any computation. I would suggest defining the type of message digest instead of using thearbitrary_dataflag.N.B.: I can generate a pull request if you wish with the modifications I outlined but it will contain the provisioning code as it is intermingled in the remote attestation process.