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.

       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:

       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, RSA_sign(3) and
           RSA_verify(3) 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.

       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.

RETURN VALUES

       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).

SEE ALSO

       ERR_get_error(3), rsa(3), RSA_sign(3), RSA_verify(3)

HISTORY

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