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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
3d866ea6 MC |
5 | EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal - EVP signing |
6 | functions | |
f7173262 DSH |
7 | |
8 | =head1 SYNOPSIS | |
9 | ||
10 | #include <openssl/evp.h> | |
11 | ||
3811eed8 DSH |
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); | |
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14 | int EVP_SignFinal(EVP_MD_CTX *ctx,unsigned char *sig,unsigned int *s, EVP_PKEY *pkey); |
15 | ||
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16 | void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type); |
17 | ||
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18 | int EVP_PKEY_size(EVP_PKEY *pkey); |
19 | ||
20 | =head1 DESCRIPTION | |
21 | ||
22 | The EVP signature routines are a high level interface to digital | |
23 | signatures. | |
24 | ||
3811eed8 | 25 | EVP_SignInit_ex() sets up signing context B<ctx> to use digest |
25191fff RL |
26 | B<type> from ENGINE B<impl>. B<ctx> must be created with |
27 | EVP_MD_CTX_new() before calling this function. | |
f7173262 DSH |
28 | |
29 | EVP_SignUpdate() hashes B<cnt> bytes of data at B<d> into the | |
c8973693 | 30 | signature context B<ctx>. This function can be called several times on the |
f7173262 DSH |
31 | same B<ctx> to include additional data. |
32 | ||
e27a2596 | 33 | EVP_SignFinal() signs the data in B<ctx> using the private key B<pkey> and |
6e6ba36d | 34 | places the signature in B<sig>. B<sig> must be at least EVP_PKEY_size(pkey) |
1afd7fa9 | 35 | bytes in size. B<s> is an OUT parameter, and not used as an IN parameter. |
6e6ba36d JW |
36 | The number of bytes of data written (i.e. the length of the signature) |
37 | will be written to the integer at B<s>, at most EVP_PKEY_size(pkey) bytes | |
38 | will be written. | |
3811eed8 DSH |
39 | |
40 | EVP_SignInit() initializes a signing context B<ctx> to use the default | |
41 | implementation of digest B<type>. | |
f7173262 DSH |
42 | |
43 | EVP_PKEY_size() returns the maximum size of a signature in bytes. The actual | |
44 | signature returned by EVP_SignFinal() may be smaller. | |
45 | ||
46 | =head1 RETURN VALUES | |
47 | ||
3811eed8 DSH |
48 | EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1 |
49 | for success and 0 for failure. | |
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50 | |
51 | EVP_PKEY_size() returns the maximum size of a signature in bytes. | |
52 | ||
9b86974e | 53 | The error codes can be obtained by L<ERR_get_error(3)>. |
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54 | |
55 | =head1 NOTES | |
56 | ||
57 | The B<EVP> interface to digital signatures should almost always be used in | |
58 | preference to the low level interfaces. This is because the code then becomes | |
59 | transparent to the algorithm used and much more flexible. | |
60 | ||
61 | Due to the link between message digests and public key algorithms the correct | |
62 | digest algorithm must be used with the correct public key type. A list of | |
63 | algorithms and associated public key algorithms appears in | |
9b86974e | 64 | L<EVP_DigestInit(3)>. |
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65 | |
66 | When signing with DSA private keys the random number generator must be seeded | |
67 | or the operation will fail. The random number generator does not need to be | |
68 | seeded for RSA signatures. | |
69 | ||
3811eed8 DSH |
70 | The call to EVP_SignFinal() internally finalizes a copy of the digest context. |
71 | This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called | |
72 | later to digest and sign additional data. | |
73 | ||
74 | Since only a copy of the digest context is ever finalized the context must | |
75 | be cleaned up after use by calling EVP_MD_CTX_cleanup() or a memory leak | |
76 | will occur. | |
77 | ||
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78 | =head1 BUGS |
79 | ||
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80 | Older versions of this documentation wrongly stated that calls to |
81 | EVP_SignUpdate() could not be made after calling EVP_SignFinal(). | |
f7173262 | 82 | |
29cf84c6 DSH |
83 | Since the private key is passed in the call to EVP_SignFinal() any error |
84 | relating to the private key (for example an unsuitable key and digest | |
85 | combination) will not be indicated until after potentially large amounts of | |
86 | data have been passed through EVP_SignUpdate(). | |
87 | ||
88 | It is not possible to change the signing parameters using these function. | |
89 | ||
90 | The previous two bugs are fixed in the newer EVP_SignDigest*() function. | |
91 | ||
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92 | =head1 SEE ALSO |
93 | ||
9b86974e RS |
94 | L<EVP_VerifyInit(3)>, |
95 | L<EVP_DigestInit(3)>, L<err(3)>, | |
96 | L<evp(3)>, L<hmac(3)>, L<md2(3)>, | |
97 | L<md5(3)>, L<mdc2(3)>, L<ripemd(3)>, | |
98 | L<sha(3)>, L<dgst(1)> | |
f7173262 | 99 | |
f7173262 | 100 | =cut |
e2f92610 RS |
101 | |
102 | =head1 COPYRIGHT | |
103 | ||
104 | Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved. | |
105 | ||
106 | Licensed under the OpenSSL license (the "License"). You may not use | |
107 | this file except in compliance with the License. You can obtain a copy | |
108 | in the file LICENSE in the source distribution or at | |
109 | L<https://www.openssl.org/source/license.html>. | |
110 | ||
111 | =cut |