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1=pod
2
3=head1 NAME
4
5EVP_SignInit, EVP_SignUpdate, EVP_SignFinal, EVP_PKEY_size
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 int EVP_PKEY_size(EVP_PKEY *pkey);
19
20=head1 DESCRIPTION
21
22The EVP signature routines are a high level interface to digital
23signatures.
24
25EVP_SignInit_ex() sets up signing context B<ctx> to use digest
26B<type> from ENGINE B<impl>. B<ctx> must be initialized with
27EVP_MD_CTX_init() before calling this function.
28
29EVP_SignUpdate() hashes B<cnt> bytes of data at B<d> into the
30signature context B<ctx>. This function can be called several times on the
31same B<ctx> to include additional data.
32
33EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and
34places the signature in B<sig>. B<sig> must be at least EVP_PKEY_size(pkey)
35bytes in size. B<s> is an OUT parameter, and not used as an IN parameter.
36The number of bytes of data written (i.e. the length of the signature)
37will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes
38will be written.
39
40EVP_SignInit() initializes a signing context B<ctx> to use the default
41implementation of digest B<type>.
42
43EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual
44signature returned by EVP_SignFinal() may be smaller.
45
46=head1 RETURN VALUES
47
48EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1
49for success and 0 for failure.
50
51EVP_PKEY_size() returns the maximum size of a signature in bytes.
52
53The error codes can be obtained by L<ERR_get_error(3)|ERR_get_error(3)>.
54
55=head1 NOTES
56
57The B<EVP> interface to digital signatures should almost always be used in
58preference to the low level interfaces. This is because the code then becomes
59transparent to the algorithm used and much more flexible.
60
61Due to the link between message digests and public key algorithms the correct
62digest algorithm must be used with the correct public key type. A list of
63algorithms and associated public key algorithms appears in
64L<EVP_DigestInit(3)|EVP_DigestInit(3)>.
65
66The call to EVP_SignFinal() internally finalizes a copy of the digest context.
67This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called
68later to digest and sign additional data.
69
70Since only a copy of the digest context is ever finalized the context must
71be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak
72will occur.
73
74=head1 BUGS
75
76Older versions of this documentation wrongly stated that calls to
77EVP_SignUpdate() could not be made after calling EVP_SignFinal().
78
79Since the private key is passed in the call to EVP_SignFinal() any error
80relating to the private key (for example an unsuitable key and digest
81combination) will not be indicated until after potentially large amounts of
82data have been passed through EVP_SignUpdate().
83
84It is not possible to change the signing parameters using these function.
85
86The previous two bugs are fixed in the newer EVP_SignDigest*() function.
87
88=head1 SEE ALSO
89
90L<EVP_VerifyInit(3)|EVP_VerifyInit(3)>,
91L<EVP_DigestInit(3)|EVP_DigestInit(3)>, L<err(3)|err(3)>,
92L<evp(3)|evp(3)>, L<hmac(3)|hmac(3)>, L<md2(3)|md2(3)>,
93L<md5(3)|md5(3)>, L<ripemd(3)|ripemd(3)>,
94L<sha(3)|sha(3)>, L<dgst(1)|dgst(1)>
95
96=head1 HISTORY
97
98EVP_SignInit(), EVP_SignUpdate() and EVP_SignFinal() are
99available in all versions of SSLeay and OpenSSL.
100
101EVP_SignInit_ex() was added in OpenSSL 0.9.7.
102
103=cut