1=pod
2
3=head1 NAME
4
5EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate,
6EVP_SignFinal_ex, EVP_SignFinal
7- EVP signing functions
8
9=head1 SYNOPSIS
10
11 #include <openssl/evp.h>
12
13 int EVP_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
14 int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
15 int EVP_SignFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s,
16                      EVP_PKEY *pkey, OSSL_LIB_CTX *libctx, const char *propq);
17 int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s,
18                   EVP_PKEY *pkey);
19
20 void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);
21
22=head1 DESCRIPTION
23
24The EVP signature routines are a high-level interface to digital
25signatures.
26
27EVP_SignInit_ex() sets up signing context I<ctx> to use digest
28I<type> from B<ENGINE> I<impl>. I<ctx> must be created with
29EVP_MD_CTX_new() before calling this function.
30
31EVP_SignUpdate() hashes I<cnt> bytes of data at I<d> into the
32signature context I<ctx>. This function can be called several times on the
33same I<ctx> to include additional data.
34
35EVP_SignFinal_ex() signs the data in I<ctx> using the private key
36I<pkey> and places the signature in I<sig>. The library context I<libctx> and
37property query I<propq> are used when creating a context to use with the key
38I<pkey>. I<sig> must be at least C<EVP_PKEY_get_size(pkey)> bytes in size.
39I<s> is an OUT parameter, and not used as an IN parameter.
40The number of bytes of data written (i.e. the length of the signature)
41will be written to the integer at I<s>, at most C<EVP_PKEY_get_size(pkey)>
42bytes will be written.
43
44EVP_SignFinal() is similar to EVP_SignFinal_ex() but uses default
45values of NULL for the library context I<libctx> and the property query I<propq>.
46
47EVP_SignInit() initializes a signing context I<ctx> to use the default
48implementation of digest I<type>.
49
50=head1 RETURN VALUES
51
52EVP_SignInit_ex(), EVP_SignUpdate(), EVP_SignFinal_ex() and
53EVP_SignFinal() return 1 for success and 0 for failure.
54
55The error codes can be obtained by L<ERR_get_error(3)>.
56
57=head1 NOTES
58
59The B<EVP> interface to digital signatures should almost always be used in
60preference to the low-level interfaces. This is because the code then becomes
61transparent to the algorithm used and much more flexible.
62
63When signing with DSA private keys the random number generator must be seeded.
64If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
65external circumstances (see L<RAND(7)>), the operation will fail.
66This requirement does not hold for RSA signatures.
67
68The call to EVP_SignFinal() internally finalizes a copy of the digest context.
69This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called
70later to digest and sign additional data.
71
72Since only a copy of the digest context is ever finalized the context must
73be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak
74will occur.
75
76=head1 BUGS
77
78Older versions of this documentation wrongly stated that calls to
79EVP_SignUpdate() could not be made after calling EVP_SignFinal().
80
81Since the private key is passed in the call to EVP_SignFinal() any error
82relating to the private key (for example an unsuitable key and digest
83combination) will not be indicated until after potentially large amounts of
84data have been passed through EVP_SignUpdate().
85
86It is not possible to change the signing parameters using these function.
87
88The previous two bugs are fixed in the newer EVP_SignDigest*() function.
89
90=head1 SEE ALSO
91
92L<EVP_PKEY_get_size(3)>, L<EVP_PKEY_get_bits(3)>,
93L<EVP_PKEY_get_security_bits(3)>,
94L<EVP_VerifyInit(3)>,
95L<EVP_DigestInit(3)>,
96L<evp(7)>, L<HMAC(3)>, L<MD2(3)>,
97L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>,
98L<SHA1(3)>, L<openssl-dgst(1)>
99
100=head1 HISTORY
101
102The function EVP_SignFinal_ex() was added in OpenSSL 3.0.
103
104=head1 COPYRIGHT
105
106Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
107
108Licensed under the Apache License 2.0 (the "License").  You may not use
109this file except in compliance with the License.  You can obtain a copy
110in the file LICENSE in the source distribution or at
111L<https://www.openssl.org/source/license.html>.
112
113=cut
114