NAME

       RSA_padding_add_PKCS1_type_1, RSA_padding_check_PKCS1_type_1, RSA_padding_add_PKCS1_type_2,
       RSA_padding_check_PKCS1_type_2, RSA_padding_add_PKCS1_OAEP, RSA_padding_check_PKCS1_OAEP,
       RSA_padding_add_PKCS1_OAEP_mgf1, RSA_padding_check_PKCS1_OAEP_mgf1, RSA_padding_add_none,
       RSA_padding_check_none - asymmetric encryption padding

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_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
                                         const unsigned char *f, int fl);

        int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
                                           const unsigned char *f, int fl, int rsa_len);

        int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
                                         const unsigned char *f, int fl);

        int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
                                           const unsigned char *f, int fl, int rsa_len);

        int RSA_padding_add_PKCS1_OAEP(unsigned char *to, int tlen,
                                       const unsigned char *f, int fl,
                                       const unsigned char *p, int pl);

        int RSA_padding_check_PKCS1_OAEP(unsigned char *to, int tlen,
                                         const unsigned char *f, int fl, int rsa_len,
                                         const unsigned char *p, int pl);

        int RSA_padding_add_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
                                            const unsigned char *f, int fl,
                                            const unsigned char *p, int pl,
                                            const EVP_MD *md, const EVP_MD *mgf1md);

        int RSA_padding_check_PKCS1_OAEP_mgf1(unsigned char *to, int tlen,
                                              const unsigned char *f, int fl, int rsa_len,
                                              const unsigned char *p, int pl,
                                              const EVP_MD *md, const EVP_MD *mgf1md);

        int RSA_padding_add_none(unsigned char *to, int tlen,
                                 const unsigned char *f, int fl);

        int RSA_padding_check_none(unsigned char *to, int tlen,
                                   const unsigned char *f, int fl, int rsa_len);

DESCRIPTION

       All of the functions described on this page are deprecated.  Applications should instead use the EVP PKEY
       APIs.

       The RSA_padding_xxx_xxx() functions are called from the RSA encrypt, decrypt, sign and verify functions.
       Normally they should not be called from application programs.

       However, they can also be called directly to implement padding for other asymmetric ciphers.
       RSA_padding_add_PKCS1_OAEP() and RSA_padding_check_PKCS1_OAEP() may be used in an application combined
       with RSA_NO_PADDING in order to implement OAEP with an encoding parameter.

       RSA_padding_add_xxx() encodes fl bytes from f so as to fit into tlen bytes and stores the result at to.
       An error occurs if fl does not meet the size requirements of the encoding method.

       The following encoding methods are implemented:

       PKCS1_type_1
           PKCS #1 v2.0 EMSA-PKCS1-v1_5 (PKCS #1 v1.5 block type 1); used for signatures

       PKCS1_type_2
           PKCS #1 v2.0 EME-PKCS1-v1_5 (PKCS #1 v1.5 block type 2)

       PKCS1_OAEP
           PKCS #1 v2.0 EME-OAEP

       none
           simply copy the data

       The random number generator must be seeded prior to calling RSA_padding_add_xxx().  If the automatic
       seeding or reseeding of the OpenSSL CSPRNG fails due to external circumstances (see RAND(7)), the
       operation will fail.

       RSA_padding_check_xxx() verifies that the fl bytes at f contain a valid encoding for a rsa_len byte RSA
       key in the respective encoding method and stores the recovered data of at most tlen bytes (for
       RSA_NO_PADDING: of size tlen) at to.

       For RSA_padding_xxx_OAEP(), p points to the encoding parameter of length pl. p may be NULL if pl is 0.

       For RSA_padding_xxx_OAEP_mgf1(), md points to the md hash, if md is NULL that means md=sha1, and mgf1md
       points to the mgf1 hash, if mgf1md is NULL that means mgf1md=md.

RETURN VALUES

       The RSA_padding_add_xxx() functions return 1 on success, 0 on error.  The RSA_padding_check_xxx()
       functions return the length of the recovered data, -1 on error. Error codes can be obtained by calling
       ERR_get_error(3).

WARNINGS

       The result of RSA_padding_check_PKCS1_type_2() is exactly the information which is used to mount a
       classical Bleichenbacher padding oracle attack. This is an inherent weakness in the PKCS #1 v1.5 padding
       design. Prefer PKCS1_OAEP padding. If that is not possible, the result of
       RSA_padding_check_PKCS1_type_2() should be checked in constant time if it matches the expected length of
       the plaintext and additionally some application specific consistency checks on the plaintext need to be
       performed in constant time.  If the plaintext is rejected it must be kept secret which of the checks
       caused the application to reject the message.  Do not remove the zero-padding from the decrypted raw RSA
       data which was computed by RSA_private_decrypt() with RSA_NO_PADDING, as this would create a small timing
       side channel which could be used to mount a Bleichenbacher attack against any padding mode including
       PKCS1_OAEP.

       You should prefer the use of EVP PKEY APIs for PKCS#1 v1.5 decryption as they implement the necessary
       workarounds internally.

SEE ALSO

       RSA_public_encrypt(3), RSA_private_decrypt(3), RSA_sign(3), RSA_verify(3), RAND(7)

HISTORY

       All 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>.