On Thu, Oct 28, 2010, Bob Dijck wrote: > Hello, > > I am trying to implement a signing function in C++ using RSA. Here's how I > wanted to do this: - First I calculate the SHA1 hash (not using openssl but > another implementation). - But then what? Should I use RSA_private_encrypt > or rsa_sign? When I use RSA_private_encrypt the result is different from > when I use rsa_sign... The openssl support pages mention that in case of > RSA_PKCS1_PADDING (that's the one I use) I should use rsa_sign. Is there any > way around this? > > I thought that signing was a two step process: hash + RSA encryption of > hash. Am I doing something wrong? >
The usual form of RSA signature is a three step process. Calculate hash, encapsulate hash in a DigestInfo structure, RSA private key encrypt the structure. If you use RSA_sign() all three steps are performed, for RSA_private_encrypt() the encapsulation is not performed. Steve. -- Dr Stephen N. Henson. OpenSSL project core developer. Commercial tech support now available see: http://www.openssl.org ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
