focal (3) RSA_private_decrypt.3ssl.gz

Provided by: libssl-doc_1.1.1f-1ubuntu2.24_all bug

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 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>.