I've combed through the cryptography manual and looked at options for ippsRSASign_PKCS1v15 but am looking for not using a hash digest. At the moment am using the base ippsRSA_Encrypt to make signatures and setting up an RSA key for the purpose of signing. But it has some performance overhead from loading the message into a BigNumberState and setting things up. Have also looked at using the function ippsRSAEncrypt_PKCSv15 since I'm using the PKCSv15 format anyway, but in using it I would need access to altering the first couple bytes of the padding which it seems the function does not allow to be done ("00020001FFFFFFFFF" attempt with using the padding pointer parameter)
Is there a way to go about just signing a message without having a hash involved that may have less overhead than my current approach?
Can you add some clarification on your problem? Actually, we can not understand the real issue there. If you can post some pseudo-code, that will be more helpful to understand your problem.
Thanks for getting back to me. It is with RSA Private Key Encryption but without creating a message digest, hash, of the input before doing the signature.
Intel Sign Operation:
Message to Sign -> Hash of Message
Hash of Message -> Padded Hash of Message
Padded Hash of Message -> Private Key Encryption of Padded Hash of Message
I want to eliminate the Hash of Message in the RSA sign operation because I can not guarantee the side doing verification knows the Hash algorithm being used.
The issue is resolved in a sense. Have created the RSA Sign operation by using Intel Montgomery and Big Number function calls.