int RSA_sign(int type, const unsigned char *m, unsigned int m_len, unsigned char *sigret, unsigned int *siglen, RSA *rsa);
int RSA_verify(int type, const unsigned char *m, unsigned int m_len, unsigned char *sigbuf, unsigned int siglen, RSA *rsa);
RSA_sign() signs the message digest m of size m_len using the private key rsa as specified in PKCS #1 v2.0. It stores the signature in sigret and the signature size in siglen. sigret must point to RSA_size(rsa) bytes of memory. Note that PKCS #1 adds meta-data, placing limits on the size of the key that can be used. See RSA_private_encrypt(3) for lower-level operations.
type denotes the message digest algorithm that was used to generate m. It usually is one of NID_sha1, NID_ripemd160 and NID_md5; see objects(3) for details. If type is NID_md5_sha1, an SSL signature (MD5 and SHA1 message digests with PKCS #1 padding and no algorithm identifier) is created.
RSA_verify() verifies that the signature sigbuf of size siglen matches a given message digest m of size m_len. type denotes the message digest algorithm that was used to generate the signature. rsa is the signer's public key.
RSA_sign() returns 1 on success, 0 otherwise. RSA_verify() returns 1 on successful verification, 0 otherwise.
The error codes can be obtained by ERR_get_error(3).
Certain signatures with an improper algorithm identifier are accepted for compatibility with SSLeay 0.4.5 :-)