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132 lines
4.8 KiB
Plaintext
132 lines
4.8 KiB
Plaintext
=pod
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=head1 NAME
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RSA_public_encrypt, RSA_private_decrypt - RSA public key cryptography
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=head1 SYNOPSIS
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#include <openssl/rsa.h>
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The following functions have been deprecated since OpenSSL 3.0, and can be
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hidden entirely by defining B<OPENSSL_API_COMPAT> with a suitable version value,
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see L<openssl_user_macros(7)>:
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int RSA_public_encrypt(int flen, const unsigned char *from,
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unsigned char *to, RSA *rsa, int padding);
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int RSA_private_decrypt(int flen, const unsigned char *from,
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unsigned char *to, RSA *rsa, int padding);
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=head1 DESCRIPTION
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Both of the functions described on this page are deprecated.
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Applications should instead use L<EVP_PKEY_encrypt_init_ex(3)>,
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L<EVP_PKEY_encrypt(3)>, L<EVP_PKEY_decrypt_init_ex(3)> and
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L<EVP_PKEY_decrypt(3)>.
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RSA_public_encrypt() encrypts the B<flen> bytes at B<from> (usually a
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session key) using the public key B<rsa> and stores the ciphertext in
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B<to>. B<to> must point to RSA_size(B<rsa>) bytes of memory.
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B<padding> denotes one of the following modes:
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=over 4
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=item RSA_PKCS1_PADDING
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PKCS #1 v1.5 padding. This currently is the most widely used mode.
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However, it is highly recommended to use RSA_PKCS1_OAEP_PADDING in
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new applications. SEE WARNING BELOW.
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=item RSA_PKCS1_OAEP_PADDING
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EME-OAEP as defined in PKCS #1 v2.0 with SHA-1, MGF1 and an empty
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encoding parameter. This mode is recommended for all new applications.
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=item RSA_NO_PADDING
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Raw RSA encryption. This mode should I<only> be used to implement
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cryptographically sound padding modes in the application code.
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Encrypting user data directly with RSA is insecure.
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=back
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When encrypting B<flen> must not be more than RSA_size(B<rsa>) - 11 for the
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PKCS #1 v1.5 based padding modes, not more than RSA_size(B<rsa>) - 42 for
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RSA_PKCS1_OAEP_PADDING and exactly RSA_size(B<rsa>) for RSA_NO_PADDING.
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When a padding mode other than RSA_NO_PADDING is in use, then
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RSA_public_encrypt() will include some random bytes into the ciphertext
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and therefore the ciphertext will be different each time, even if the
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plaintext and the public key are exactly identical.
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The returned ciphertext in B<to> will always be zero padded to exactly
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RSA_size(B<rsa>) bytes.
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B<to> and B<from> may overlap.
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RSA_private_decrypt() decrypts the B<flen> bytes at B<from> using the
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private key B<rsa> and stores the plaintext in B<to>. B<flen> should
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be equal to RSA_size(B<rsa>) but may be smaller, when leading zero
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bytes are in the ciphertext. Those are not important and may be removed,
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but RSA_public_encrypt() does not do that. B<to> must point
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to a memory section large enough to hold the maximal possible decrypted
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data (which is equal to RSA_size(B<rsa>) for RSA_NO_PADDING,
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RSA_size(B<rsa>) - 11 for the PKCS #1 v1.5 based padding modes and
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RSA_size(B<rsa>) - 42 for RSA_PKCS1_OAEP_PADDING).
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B<padding> is the padding mode that was used to encrypt the data.
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B<to> and B<from> may overlap.
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=head1 RETURN VALUES
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RSA_public_encrypt() returns the size of the encrypted data (i.e.,
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RSA_size(B<rsa>)). RSA_private_decrypt() returns the size of the
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recovered plaintext. A return value of 0 is not an error and
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means only that the plaintext was empty.
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On error, -1 is returned; the error codes can be
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obtained by L<ERR_get_error(3)>.
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=head1 WARNINGS
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Decryption failures in the RSA_PKCS1_PADDING mode leak information
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which can potentially be used to mount a Bleichenbacher padding oracle
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attack. This is an inherent weakness in the PKCS #1 v1.5 padding
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design. Prefer RSA_PKCS1_OAEP_PADDING.
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In OpenSSL before version 3.2.0, both the return value and the length of
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returned value could be used to mount the Bleichenbacher attack.
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Since version 3.2.0, the default provider in OpenSSL does not return an
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error when padding checks fail. Instead it generates a random
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message based on used private
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key and provided ciphertext so that application code doesn't have to implement
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a side-channel secure error handling.
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Applications that want to be secure against side-channel attacks with
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providers that don't implement implicit rejection, still need to
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handle the returned values using side-channel free code.
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Side-channel free handling of the error stack can be performed using
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either a pair of unconditional L<ERR_set_mark(3)> and L<ERR_pop_to_mark(3)>
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calls or by using the L<ERR_clear_error(3)> call.
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=head1 CONFORMING TO
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SSL, PKCS #1 v2.0
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=head1 SEE ALSO
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L<ERR_get_error(3)>, L<RAND_bytes(3)>,
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L<RSA_size(3)>, L<EVP_PKEY_decrypt(3)>, L<EVP_PKEY_encrypt(3)>
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=head1 HISTORY
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Both of these functions were deprecated in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2000-2024 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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