1*2175Sjp161948=pod
2*2175Sjp161948
3*2175Sjp161948=head1 NAME
4*2175Sjp161948
5*2175Sjp161948RSA_private_encrypt, RSA_public_decrypt - low level signature operations
6*2175Sjp161948
7*2175Sjp161948=head1 SYNOPSIS
8*2175Sjp161948
9*2175Sjp161948 #include <openssl/rsa.h>
10*2175Sjp161948
11*2175Sjp161948 int RSA_private_encrypt(int flen, unsigned char *from,
12*2175Sjp161948    unsigned char *to, RSA *rsa, int padding);
13*2175Sjp161948
14*2175Sjp161948 int RSA_public_decrypt(int flen, unsigned char *from,
15*2175Sjp161948    unsigned char *to, RSA *rsa, int padding);
16*2175Sjp161948
17*2175Sjp161948=head1 DESCRIPTION
18*2175Sjp161948
19*2175Sjp161948These functions handle RSA signatures at a low level.
20*2175Sjp161948
21*2175Sjp161948RSA_private_encrypt() signs the B<flen> bytes at B<from> (usually a
22*2175Sjp161948message digest with an algorithm identifier) using the private key
23*2175Sjp161948B<rsa> and stores the signature in B<to>. B<to> must point to
24*2175Sjp161948B<RSA_size(rsa)> bytes of memory.
25*2175Sjp161948
26*2175Sjp161948B<padding> denotes one of the following modes:
27*2175Sjp161948
28*2175Sjp161948=over 4
29*2175Sjp161948
30*2175Sjp161948=item RSA_PKCS1_PADDING
31*2175Sjp161948
32*2175Sjp161948PKCS #1 v1.5 padding. This function does not handle the
33*2175Sjp161948B<algorithmIdentifier> specified in PKCS #1. When generating or
34*2175Sjp161948verifying PKCS #1 signatures, L<RSA_sign(3)|RSA_sign(3)> and L<RSA_verify(3)|RSA_verify(3)> should be
35*2175Sjp161948used.
36*2175Sjp161948
37*2175Sjp161948=item RSA_NO_PADDING
38*2175Sjp161948
39*2175Sjp161948Raw RSA signature. This mode should I<only> be used to implement
40*2175Sjp161948cryptographically sound padding modes in the application code.
41*2175Sjp161948Signing user data directly with RSA is insecure.
42*2175Sjp161948
43*2175Sjp161948=back
44*2175Sjp161948
45*2175Sjp161948RSA_public_decrypt() recovers the message digest from the B<flen>
46*2175Sjp161948bytes long signature at B<from> using the signer's public key
47*2175Sjp161948B<rsa>. B<to> must point to a memory section large enough to hold the
48*2175Sjp161948message digest (which is smaller than B<RSA_size(rsa) -
49*2175Sjp16194811>). B<padding> is the padding mode that was used to sign the data.
50*2175Sjp161948
51*2175Sjp161948=head1 RETURN VALUES
52*2175Sjp161948
53*2175Sjp161948RSA_private_encrypt() returns the size of the signature (i.e.,
54*2175Sjp161948RSA_size(rsa)). RSA_public_decrypt() returns the size of the
55*2175Sjp161948recovered message digest.
56*2175Sjp161948
57*2175Sjp161948On error, -1 is returned; the error codes can be
58*2175Sjp161948obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
59*2175Sjp161948
60*2175Sjp161948=head1 SEE ALSO
61*2175Sjp161948
62*2175Sjp161948L<ERR_get_error(3)|ERR_get_error(3)>, L<rsa(3)|rsa(3)>,
63*2175Sjp161948L<RSA_sign(3)|RSA_sign(3)>, L<RSA_verify(3)|RSA_verify(3)>
64*2175Sjp161948
65*2175Sjp161948=head1 HISTORY
66*2175Sjp161948
67*2175Sjp161948The B<padding> argument was added in SSLeay 0.8. RSA_NO_PADDING is
68*2175Sjp161948available since SSLeay 0.9.0.
69*2175Sjp161948
70*2175Sjp161948=cut
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