1=pod
2
3=head1 NAME
4
5EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal
6- EVP signing functions
7
8=head1 SYNOPSIS
9
10 #include <openssl/evp.h>
11
12 int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
13 int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
14 int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, EVP_PKEY *pkey);
15
16 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
17
18=head1 DESCRIPTION
19
20The EVP signature routines are a high-level interface to digital
21signatures.
22
23EVP_SignInit_ex() sets up signing context I<ctx> to use digest
24I<type> from B<ENGINE> I<impl>. I<ctx> must be created with
25EVP_MD_CTX_new() before calling this function.
26
27EVP_SignUpdate() hashes I<cnt> bytes of data at I<d> into the
28signature context I<ctx>. This function can be called several times on the
29same I<ctx> to include additional data.
30
31EVP_SignFinal() signs the data in I<ctx> using the private key I<pkey> and
32places the signature in I<sig>. I<sig> must be at least C<EVP_PKEY_size(pkey)>
33bytes in size. I<s> is an OUT parameter, and not used as an IN parameter.
34The number of bytes of data written (i.e. the length of the signature)
35will be written to the integer at I<s>, at most C<EVP_PKEY_size(pkey)> bytes
36will be written.
37
38EVP_SignInit() initializes a signing context I<ctx> to use the default
39implementation of digest I<type>.
40
41=head1 RETURN VALUES
42
43EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1
44for success and 0 for failure.
45
46The error codes can be obtained by L<ERR_get_error(3)>.
47
48=head1 NOTES
49
50The B<EVP> interface to digital signatures should almost always be used in
51preference to the low-level interfaces. This is because the code then becomes
52transparent to the algorithm used and much more flexible.
53
54When signing with DSA private keys the random number generator must be seeded.
55If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
56external circumstances (see L<RAND(7)>), the operation will fail.
57This requirement does not hold for RSA signatures.
58
59The call to EVP_SignFinal() internally finalizes a copy of the digest context.
60This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called
61later to digest and sign additional data.
62
63Since only a copy of the digest context is ever finalized the context must
64be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak
65will occur.
66
67=head1 BUGS
68
69Older versions of this documentation wrongly stated that calls to
70EVP_SignUpdate() could not be made after calling EVP_SignFinal().
71
72Since the private key is passed in the call to EVP_SignFinal() any error
73relating to the private key (for example an unsuitable key and digest
74combination) will not be indicated until after potentially large amounts of
75data have been passed through EVP_SignUpdate().
76
77It is not possible to change the signing parameters using these function.
78
79The previous two bugs are fixed in the newer EVP_SignDigest*() function.
80
81=head1 SEE ALSO
82
83L<EVP_PKEY_size(3)>, L<EVP_PKEY_bits(3)>, L<EVP_PKEY_security_bits(3)>,
84L<EVP_VerifyInit(3)>,
85L<EVP_DigestInit(3)>,
86L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
87L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
88L<SHA1(3)>, L<dgst(1)>
89
90=head1 COPYRIGHT
91
92Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved.
93
94Licensed under the OpenSSL license (the "License").  You may not use
95this file except in compliance with the License.  You can obtain a copy
96in the file LICENSE in the source distribution or at
97L<https://www.openssl.org/source/license.html>.
98
99=cut
100