=pod

=head1 NAME

RSA_public_encrypt, RSA_private_decrypt - RSA public key cryptography

=head1 SYNOPSIS

 #include <openssl/rsa.h>

 int RSA_public_encrypt(int flen, unsigned char *from,
                        unsigned char *to, RSA *rsa, int padding);

 int RSA_private_decrypt(int flen, unsigned char *from,
                         unsigned char *to, RSA *rsa, int padding);

=head1 DESCRIPTION

RSA_public_encrypt() encrypts the B<flen> bytes at B<from> (usually a
session key) using the public key B<rsa> and stores the ciphertext in
B<to>. B<to> must point to RSA_size(B<rsa>) bytes of memory.

B<padding> denotes one of the following modes:

=over 4

=item RSA_PKCS1_PADDING

PKCS #1 v1.5 padding. This currently is the most widely used mode.

=item 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.

=item RSA_SSLV23_PADDING

PKCS #1 v1.5 padding with an SSL-specific modification that denotes
that the server is SSL3 capable.

=item RSA_NO_PADDING

Raw RSA encryption. This mode should I<only> be used to implement
cryptographically sound padding modes in the application code.
Encrypting user data directly with RSA is insecure.

=back

B<flen> must be less than RSA_size(B<rsa>) - 11 for the PKCS #1 v1.5
based padding modes, less than RSA_size(B<rsa>) - 41 for
RSA_PKCS1_OAEP_PADDING and exactly RSA_size(B<rsa>) for RSA_NO_PADDING.
The random number generator must be seeded prior to calling
RSA_public_encrypt().

RSA_private_decrypt() decrypts the B<flen> bytes at B<from> using the
private key B<rsa> and stores the plaintext in B<to>. B<to> must point
to a memory section large enough to hold the decrypted data (which is
smaller than RSA_size(B<rsa>)). B<padding> is the padding mode that
was used to encrypt the data.

=head1 RETURN VALUES

RSA_public_encrypt() returns the size of the encrypted data (i.e.,
RSA_size(B<rsa>)). RSA_private_decrypt() returns the size of the
recovered plaintext.

On error, -1 is returned; the error codes can be
obtained by L<ERR_get_error(3)>.

=head1 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.

=head1 CONFORMING TO

SSL, PKCS #1 v2.0

=head1 SEE ALSO

L<ERR_get_error(3)>, L<RAND_bytes(3)>,
L<RSA_size(3)>

=head1 COPYRIGHT

Copyright 2000-2016 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
L<https://www.openssl.org/source/license.html>.

=cut
