xref: /freebsd/crypto/openssl/doc/man3/RSA_public_encrypt.pod (revision e17f5b1d307b7b8910d67883e57a9604305906d5)
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