RSA_private_encrypt, RSA_public_decrypt - low level signature operations
#include <openssl/rsa.h>
int RSA_private_encrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);
int RSA_public_decrypt(int flen, const unsigned char *from,
unsigned char *to, RSA *rsa, int padding);
These functions handle RSA signatures at a low level.
RSA_private_encrypt() signs the flen bytes at from (usually a message digest with an algorithm identifier) using the private key rsa and stores the signature in to. to must point to RSA_size(rsa) bytes of memory.
padding denotes one of the following modes:
PKCS #1 v1.5 padding. This function does not handle the algorithmIdentifier specified in PKCS #1. When generating or verifying PKCS #1 signatures, RSA_sign(3) and RSA_verify(3) should be used.
Raw RSA signature. This mode should only be used to implement cryptographically sound padding modes in the application code. Signing user data directly with RSA is insecure.
RSA_public_decrypt() recovers the message digest from the flen bytes long signature at from using the signer's public key rsa. to must point to a memory section large enough to hold the message digest (which is smaller than RSA_size(rsa) - 11). padding is the padding mode that was used to sign the data.
RSA_private_encrypt() returns the size of the signature (i.e., RSA_size(rsa)). RSA_public_decrypt() returns the size of the recovered message digest.
On error, -1 is returned; the error codes can be obtained by ERR_get_error(3).
ERR_get_error(3), rsa(3), RSA_sign(3), RSA_verify(3)
The padding argument was added in SSLeay 0.8. RSA_NO_PADDING is available since SSLeay 0.9.0.