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RSA_PUBLIC_ENCRYPT(3)               OpenSSL              RSA_PUBLIC_ENCRYPT(3)
NAME
       RSA_public_encrypt, RSA_private_decrypt - RSA public key cryptography
SYNOPSIS
        #include <openssl/rsa.h>
        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
       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_SSLV23_PADDING
           PKCS #1 v1.5 padding with an SSL-specific modification that denotes
           that the server is SSL3 capable.
       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)
COPYRIGHT
       Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
       Licensed under the OpenSSL license (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>;.
1.1.1k                            2024-10-09             RSA_PUBLIC_ENCRYPT(3)