1=pod
2
3=head1 NAME
4
5EVP_PKEY_size,
6EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal,
7EVP_PKEY_security_bits - EVP signing
8functions
9
10=head1 SYNOPSIS
11
12 #include <openssl/evp.h>
13
14 int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
15 int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
16 int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, EVP_PKEY *pkey);
17
18 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
19
20 int EVP_PKEY_size(EVP_PKEY *pkey);
21 int EVP_PKEY_security_bits(const EVP_PKEY *pkey);
22
23=head1 DESCRIPTION
24
25The EVP signature routines are a high level interface to digital
26signatures.
27
28EVP_SignInit_ex() sets up signing context B<ctx> to use digest
29B<type> from ENGINE B<impl>. B<ctx> must be created with
30EVP_MD_CTX_new() before calling this function.
31
32EVP_SignUpdate() hashes B<cnt> bytes of data at B<d> into the
33signature context B<ctx>. This function can be called several times on the
34same B<ctx> to include additional data.
35
36EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and
37places the signature in B<sig>. B<sig> must be at least EVP_PKEY_size(pkey)
38bytes in size. B<s> is an OUT parameter, and not used as an IN parameter.
39The number of bytes of data written (i.e. the length of the signature)
40will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes
41will be written.
42
43EVP_SignInit() initializes a signing context B<ctx> to use the default
44implementation of digest B<type>.
45
46EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual
47signature returned by EVP_SignFinal() may be smaller.
48
49EVP_PKEY_security_bits() returns the number of security bits of the given B<pkey>,
50bits of security is defined in NIST SP800-57.
51
52=head1 RETURN VALUES
53
54EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1
55for success and 0 for failure.
56
57EVP_PKEY_size() returns the maximum size of a signature in bytes.
58
59The error codes can be obtained by L<ERR_get_error(3)>.
60
61EVP_PKEY_security_bits() returns the number of security bits.
62
63=head1 NOTES
64
65The B<EVP> interface to digital signatures should almost always be used in
66preference to the low level interfaces. This is because the code then becomes
67transparent to the algorithm used and much more flexible.
68
69When signing with DSA private keys the random number generator must be seeded
70or the operation will fail. The random number generator does not need to be
71seeded for RSA signatures.
72
73The call to EVP_SignFinal() internally finalizes a copy of the digest context.
74This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called
75later to digest and sign additional data.
76
77Since only a copy of the digest context is ever finalized the context must
78be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak
79will occur.
80
81=head1 BUGS
82
83Older versions of this documentation wrongly stated that calls to
84EVP_SignUpdate() could not be made after calling EVP_SignFinal().
85
86Since the private key is passed in the call to EVP_SignFinal() any error
87relating to the private key (for example an unsuitable key and digest
88combination) will not be indicated until after potentially large amounts of
89data have been passed through EVP_SignUpdate().
90
91It is not possible to change the signing parameters using these function.
92
93The previous two bugs are fixed in the newer EVP_SignDigest*() function.
94
95=head1 SEE ALSO
96
97L<EVP_VerifyInit(3)>,
98L<EVP_DigestInit(3)>,
99L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
100L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
101L<SHA1(3)>, L<dgst(1)>
102
103=head1 COPYRIGHT
104
105Copyright 2000-2018 The OpenSSL Project Authors. All Rights Reserved.
106
107Licensed under the OpenSSL license (the "License").  You may not use
108this file except in compliance with the License.  You can obtain a copy
109in the file LICENSE in the source distribution or at
110L<https://www.openssl.org/source/license.html>.
111
112=cut
113