RSA_PRIVATE_ENCRYPT(3SSL) OpenSSL RSA_PRIVATE_ENCRYPT(3SSL)
NAME
RSA_private_encrypt, RSA_public_decrypt - low-level signature operations
SYNOPSIS
#include <openssl/rsa.h>
The following functions have been deprecated since OpenSSL 3.0, and can
be hidden entirely by defining OPENSSL_API_COMPAT with a suitable
version value, see openssl_user_macros(7):
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
Both of the functions described on this page are deprecated.
Applications should instead use EVP_PKEY_sign_init_ex(3),
EVP_PKEY_sign(3), EVP_PKEY_verify_recover_init(3), and
EVP_PKEY_verify_recover(3).
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_sign(3), RSA_verify(3), EVP_PKEY_sign(3),
EVP_PKEY_verify_recover(3)
HISTORY
Both of these functions were deprecated in OpenSSL 3.0.
COPYRIGHT
Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the Apache License 2.0 (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<https://www.openssl.org/source/license.html>.
3.5.7 2026-06-09 RSA_PRIVATE_ENCRYPT(3SSL)
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