NAME

       RSA_public_encrypt, RSA_private_decrypt - RSA public key cryptography

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_public_encrypt(int flen, const unsigned char *from,
                               unsigned char *to, RSA *rsa, int padding);

        int RSA_private_decrypt(int flen, const 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_encrypt_init_ex(3), EVP_PKEY_encrypt(3), EVP_PKEY_decrypt_init_ex(3) and EVP_PKEY_decrypt(3).

       RSA_public_encrypt() encrypts the flen bytes at from (usually a session key) using the public key rsa and
       stores the ciphertext 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 currently is the most widely used mode.  However, it is highly recommended
           to use RSA_PKCS1_OAEP_PADDING in new applications. SEE WARNING BELOW.

       RSA_PKCS1_OAEP_PADDING
           EME-OAEP  as  defined  in PKCS #1 v2.0 with SHA-1, MGF1 and an empty encoding parameter. This mode is
           recommended for all new applications.

       RSA_NO_PADDING
           Raw RSA encryption. This mode should only be used to implement cryptographically sound padding  modes
           in the application code.  Encrypting user data directly with RSA is insecure.

       When  encrypting  flen must not be more than RSA_size(rsa) - 11 for the PKCS #1 v1.5 based padding modes,
       not more than RSA_size(rsa) - 42 for RSA_PKCS1_OAEP_PADDING and exactly RSA_size(rsa) for RSA_NO_PADDING.
       When a padding mode other than RSA_NO_PADDING is in use,  then  RSA_public_encrypt()  will  include  some
       random  bytes  into  the ciphertext and therefore the ciphertext will be different each time, even if the
       plaintext and the public key are exactly identical.  The returned ciphertext in to will  always  be  zero
       padded to exactly RSA_size(rsa) bytes.  to and from may overlap.

       RSA_private_decrypt()  decrypts the flen bytes at from using the private key rsa and stores the plaintext
       in to. flen should be equal to RSA_size(rsa) but may be smaller, when  leading  zero  bytes  are  in  the
       ciphertext.  Those  are  not  important and may be removed, but RSA_public_encrypt() does not do that. to
       must point to a memory section large enough to hold the maximal possible decrypted data (which  is  equal
       to  RSA_size(rsa)  for  RSA_NO_PADDING,  RSA_size(rsa)  - 11 for the PKCS #1 v1.5 based padding modes and
       RSA_size(rsa) - 42 for RSA_PKCS1_OAEP_PADDING).  padding is the padding mode that was used to encrypt the
       data.  to and from may overlap.

RETURN VALUES

       RSA_public_encrypt() returns the size of the encrypted data (i.e., RSA_size(rsa)).  RSA_private_decrypt()
       returns  the size of the recovered plaintext. A return value of 0 is not an error and means only that the
       plaintext was empty.

       On error, -1 is returned; the error codes can be obtained by ERR_get_error(3).

WARNINGS

       Decryption failures in the RSA_PKCS1_PADDING mode leak information which can potentially be used to mount
       a Bleichenbacher padding oracle attack. This is an inherent weakness in the PKCS #1 v1.5 padding  design.
       Prefer RSA_PKCS1_OAEP_PADDING.

       In  OpenSSL before version 3.1.0, both the return value and the length of returned value could be used to
       mount the Bleichenbacher attack.  Since version 3.1.0, OpenSSL does  not  return  an  error  in  case  of
       padding  checks  failed.  Instead  it  generates  a random message based on used private key and provided
       ciphertext so that application code doesn't have to implement a side-channel secure error handling.

CONFORMING TO

       SSL, PKCS #1 v2.0

SEE ALSO

       ERR_get_error(3), RAND_bytes(3), RSA_size(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>.

3.0.13                                             2025-02-05                           RSA_PUBLIC_ENCRYPT(3SSL)