RSA_private_encrypt(3)

     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.