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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.

       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).

WARNING

       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.

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>.