NAME

RSA_private_encrypt, RSA_public_decrypt − Low level signature operations

SYNOPSIS

#include <openssl/rsa.h>
int RSA_private_encrypt(
        int flen, unsigned char ∗from, unsigned char ∗to, RSA ∗rsa, int padding ); int RSA_public_decrypt(
        int flen, unsigned char ∗from, unsigned char ∗to, RSA ∗rsa, int padding );

DESCRIPTION

These functions handle RSA signatures at a low level. 

The RSA_private_encrypt() function 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. The to must point to RSA_size(rsa) bytes of memory. 

The padding denotes one of the following modes:

RSA_PKCS1_PADDING
PKCS #1 v1.5 padding. This function does not handle the algorithmIdentifier specified in PKCS #1. When generating or verifying PKCS #1 signatures, the RSA_sign() and RSA_verify() functions should be used. 

RSA_NO_PADDING
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.

The RSA_public_decrypt() function recovers the message digest from the flen bytes long signature at from using the signer’s public key rsa. The to must point to a memory section large enough to hold the message digest (which is smaller than RSA_size(rsa) - 11). The padding is the padding mode that was used to sign the data. 

RETURN VALUES

The RSA_private_encrypt() function returns the size of the signature (i.e., RSA_size(rsa)). The RSA_public_decrypt() function returns the size of the recovered message digest. 

On error, -1 is returned; the error codes can be obtained by using the ERR_get_error() function. 

HISTORY

The padding argument was added in SSLeay 0.8. RSA_NO_PADDING is available since SSLeay 0.9.0. 

SEE ALSO

Functions: err(3), rsa(3), RSA_sign(3), RSA_verify(3)