RSA_PRIVATE_ENCRYPT(3)     Library Functions Manual     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, 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);

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
     RSA_meth_set_priv_enc(3), RSA_new(3), RSA_sign(3), RSA_verify(3)

HISTORY
     RSA_private_encrypt() and RSA_public_decrypt() appeared in SSLeay 0.4 or
     earlier and have been available since OpenBSD 2.4.

     RSA_NO_PADDING is available since SSLeay 0.9.0.

Linux 6.8.2-arch2-1              June 10, 2019             Linux 6.8.2-arch2-1