1=pod 2 3=head1 NAME 4 5RSA_public_encrypt, RSA_private_decrypt - RSA public key cryptography 6 7=head1 SYNOPSIS 8 9 #include <openssl/rsa.h> 10 11 int RSA_public_encrypt(int flen, const unsigned char *from, 12 unsigned char *to, RSA *rsa, int padding); 13 14 int RSA_private_decrypt(int flen, const unsigned char *from, 15 unsigned char *to, RSA *rsa, int padding); 16 17=head1 DESCRIPTION 18 19RSA_public_encrypt() encrypts the B<flen> bytes at B<from> (usually a 20session key) using the public key B<rsa> and stores the ciphertext in 21B<to>. B<to> must point to RSA_size(B<rsa>) bytes of memory. 22 23B<padding> denotes one of the following modes: 24 25=over 4 26 27=item RSA_PKCS1_PADDING 28 29PKCS #1 v1.5 padding. This currently is the most widely used mode. 30However, it is highly recommended to use RSA_PKCS1_OAEP_PADDING in 31new applications. SEE WARNING BELOW. 32 33=item RSA_PKCS1_OAEP_PADDING 34 35EME-OAEP as defined in PKCS #1 v2.0 with SHA-1, MGF1 and an empty 36encoding parameter. This mode is recommended for all new applications. 37 38=item RSA_SSLV23_PADDING 39 40PKCS #1 v1.5 padding with an SSL-specific modification that denotes 41that the server is SSL3 capable. 42 43=item RSA_NO_PADDING 44 45Raw RSA encryption. This mode should I<only> be used to implement 46cryptographically sound padding modes in the application code. 47Encrypting user data directly with RSA is insecure. 48 49=back 50 51B<flen> must not be more than RSA_size(B<rsa>) - 11 for the PKCS #1 v1.5 52based padding modes, not more than RSA_size(B<rsa>) - 42 for 53RSA_PKCS1_OAEP_PADDING and exactly RSA_size(B<rsa>) for RSA_NO_PADDING. 54When a padding mode other than RSA_NO_PADDING is in use, then 55RSA_public_encrypt() will include some random bytes into the ciphertext 56and therefore the ciphertext will be different each time, even if the 57plaintext and the public key are exactly identical. 58The returned ciphertext in B<to> will always be zero padded to exactly 59RSA_size(B<rsa>) bytes. 60B<to> and B<from> may overlap. 61 62RSA_private_decrypt() decrypts the B<flen> bytes at B<from> using the 63private key B<rsa> and stores the plaintext in B<to>. B<flen> should 64be equal to RSA_size(B<rsa>) but may be smaller, when leading zero 65bytes are in the ciphertext. Those are not important and may be removed, 66but RSA_public_encrypt() does not do that. B<to> must point 67to a memory section large enough to hold the maximal possible decrypted 68data (which is equal to RSA_size(B<rsa>) for RSA_NO_PADDING, 69RSA_size(B<rsa>) - 11 for the PKCS #1 v1.5 based padding modes and 70RSA_size(B<rsa>) - 42 for RSA_PKCS1_OAEP_PADDING). 71B<padding> is the padding mode that was used to encrypt the data. 72B<to> and B<from> may overlap. 73 74=head1 RETURN VALUES 75 76RSA_public_encrypt() returns the size of the encrypted data (i.e., 77RSA_size(B<rsa>)). RSA_private_decrypt() returns the size of the 78recovered plaintext. A return value of 0 is not an error and 79means only that the plaintext was empty. 80 81On error, -1 is returned; the error codes can be 82obtained by L<ERR_get_error(3)>. 83 84=head1 WARNINGS 85 86Decryption failures in the RSA_PKCS1_PADDING mode leak information 87which can potentially be used to mount a Bleichenbacher padding oracle 88attack. This is an inherent weakness in the PKCS #1 v1.5 padding 89design. Prefer RSA_PKCS1_OAEP_PADDING. 90 91=head1 CONFORMING TO 92 93SSL, PKCS #1 v2.0 94 95=head1 SEE ALSO 96 97L<ERR_get_error(3)>, L<RAND_bytes(3)>, 98L<RSA_size(3)> 99 100=head1 COPYRIGHT 101 102Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved. 103 104Licensed under the OpenSSL license (the "License"). You may not use 105this file except in compliance with the License. You can obtain a copy 106in the file LICENSE in the source distribution or at 107L<https://www.openssl.org/source/license.html>. 108 109=cut 110