咨询SGX中sgx_ecc256_compute_shared_dhkey()使用的椭圆曲线及OpenSSL适配问题

Great question! Let's break this down clearly for you:

The sgx_ecc256_compute_shared_dhkey() function (alongside all other functions in SGX's ECC256 API family, like sgx_ecc256_create_key_pair() or sgx_ecc256_sign()) uses the NIST P-256 elliptic curve (also known as secp256r1 or prime256v1). This is a widely standardized curve, so it’s fully compatible with OpenSSL’s native support for the same curve.

Here's a step-by-step guide to get your key exchange working smoothly:

• Confirm OpenSSL supports P-256: First, check that your OpenSSL installation includes support for the curve. Run this terminal command:

  openssl ecparam -list_curves | grep -E "(secp256r1|prime256v1)"
  

  You should see an entry for either name (they refer to the exact same curve).

• Generate SGX ECC key pair: Use SGX’s sgx_ecc256_create_key_pair() to generate a private/public key pair. The public key is stored in a sgx_ec256_public_t struct, which contains two 32-byte fields: gx (x-coordinate) and gy (y-coordinate).

• Generate OpenSSL P-256 key pair: Create your OpenSSL key pair using the P-256 curve. You can do this via command line:

  # Generate private key
  openssl ecparam -name secp256r1 -genkey -out openssl_private.pem
  # Extract public key
  openssl ec -in openssl_private.pem -pubout -out openssl_public.pem
  

  Or programmatically using OpenSSL’s C API (initialize with EVP_PKEY_CTX_new_id(EVP_PKEY_EC) and set the curve to secp256r1).

• Exchange public keys between SGX and OpenSSL:

  • For SGX → OpenSSL: Convert the sgx_ec256_public_t struct to a standard uncompressed ECC public key format:
    1. Prepend a 0x04 byte (to mark it as an uncompressed public key)
    2. Append the 32-byte gx value (big-endian, which matches NIST standards)
    3. Append the 32-byte gy value (also big-endian)
       Import this 65-byte raw key into OpenSSL using EC_POINT_oct2point() or d2i_EC_PUBKEY().
  • For OpenSSL → SGX: Extract the raw x and y coordinates from your OpenSSL public key, then copy them into the gx and gy fields of a sgx_ec256_public_t struct.

• Compute shared DH key on both sides:

  • SGX side: Call sgx_ecc256_compute_shared_dhkey() with your SGX private key and the imported OpenSSL public key.
  • OpenSSL side: Use the EVP_PKEY_derive() function with your OpenSSL private key and the converted SGX public key to compute the identical shared secret.

• Stick to big-endian format: SGX’s ECC coordinates use big-endian byte order, which aligns with OpenSSL’s default handling of P-256 keys—no byte-swapping is needed if you follow the format conversion steps above.
• Secure private keys: Never expose SGX enclave private keys outside the enclave, and handle OpenSSL private keys with standard secure practices (like encrypted storage).
• Validate public keys: Before computing the shared secret, validate that the received public key is a valid point on the P-256 curve. Use SGX’s sgx_ecc256_check_point() function on the enclave side for this.

内容的提问来源于stack exchange，提问作者Bean