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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
eed9d03b RL |
5 | EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal |
6 | - EVP signing 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); | |
aebb9aac | 14 | int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, EVP_PKEY *pkey); |
f7173262 | 15 | |
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16 | void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type); |
17 | ||
f7173262 DSH |
18 | =head1 DESCRIPTION |
19 | ||
20 | The EVP signature routines are a high level interface to digital | |
21 | signatures. | |
22 | ||
53418932 RL |
23 | EVP_SignInit_ex() sets up signing context I<ctx> to use digest |
24 | I<type> from B<ENGINE> I<impl>. I<ctx> must be created with | |
25191fff | 25 | EVP_MD_CTX_new() before calling this function. |
f7173262 | 26 | |
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27 | EVP_SignUpdate() hashes I<cnt> bytes of data at I<d> into the |
28 | signature context I<ctx>. This function can be called several times on the | |
29 | same I<ctx> to include additional data. | |
f7173262 | 30 | |
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31 | EVP_SignFinal() signs the data in I<ctx> using the private key I<pkey> and |
32 | places the signature in I<sig>. I<sig> must be at least C<EVP_PKEY_size(pkey)> | |
33 | bytes in size. I<s> is an OUT parameter, and not used as an IN parameter. | |
6e6ba36d | 34 | The number of bytes of data written (i.e. the length of the signature) |
53418932 | 35 | will be written to the integer at I<s>, at most C<EVP_PKEY_size(pkey)> bytes |
6e6ba36d | 36 | will be written. |
3811eed8 | 37 | |
53418932 RL |
38 | EVP_SignInit() initializes a signing context I<ctx> to use the default |
39 | implementation of digest I<type>. | |
f7173262 | 40 | |
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41 | =head1 RETURN VALUES |
42 | ||
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43 | EVP_SignInit_ex(), EVP_SignUpdate() and EVP_SignFinal() return 1 |
44 | for success and 0 for failure. | |
f7173262 | 45 | |
9b86974e | 46 | The error codes can be obtained by L<ERR_get_error(3)>. |
f7173262 DSH |
47 | |
48 | =head1 NOTES | |
49 | ||
50 | The B<EVP> interface to digital signatures should almost always be used in | |
51 | preference to the low level interfaces. This is because the code then becomes | |
52 | transparent to the algorithm used and much more flexible. | |
53 | ||
f987a4dd DMSP |
54 | When signing with DSA private keys the random number generator must be seeded. |
55 | If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to | |
56 | external circumstances (see L<RAND(7)>), the operation will fail. | |
57 | This requirement does not hold for RSA signatures. | |
f7173262 | 58 | |
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59 | The call to EVP_SignFinal() internally finalizes a copy of the digest context. |
60 | This means that calls to EVP_SignUpdate() and EVP_SignFinal() can be called | |
61 | later to digest and sign additional data. | |
62 | ||
63 | Since only a copy of the digest context is ever finalized the context must | |
c12a2d27 | 64 | be cleaned up after use by calling EVP_MD_CTX_free() or a memory leak |
3811eed8 DSH |
65 | will occur. |
66 | ||
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67 | =head1 BUGS |
68 | ||
1bc74519 | 69 | Older versions of this documentation wrongly stated that calls to |
3811eed8 | 70 | EVP_SignUpdate() could not be made after calling EVP_SignFinal(). |
f7173262 | 71 | |
29cf84c6 DSH |
72 | Since the private key is passed in the call to EVP_SignFinal() any error |
73 | relating to the private key (for example an unsuitable key and digest | |
74 | combination) will not be indicated until after potentially large amounts of | |
75 | data have been passed through EVP_SignUpdate(). | |
76 | ||
77 | It is not possible to change the signing parameters using these function. | |
78 | ||
79 | The previous two bugs are fixed in the newer EVP_SignDigest*() function. | |
80 | ||
f7173262 DSH |
81 | =head1 SEE ALSO |
82 | ||
eed9d03b | 83 | L<EVP_PKEY_size(3)>, L<EVP_PKEY_bits(3)>, L<EVP_PKEY_security_bits(3)>, |
9b86974e | 84 | L<EVP_VerifyInit(3)>, |
73fb82b7 | 85 | L<EVP_DigestInit(3)>, |
b97fdb57 RL |
86 | L<evp(7)>, L<HMAC(3)>, L<MD2(3)>, |
87 | L<MD5(3)>, L<MDC2(3)>, L<RIPEMD160(3)>, | |
88 | L<SHA1(3)>, L<dgst(1)> | |
f7173262 | 89 | |
e2f92610 RS |
90 | =head1 COPYRIGHT |
91 | ||
e7ff223a | 92 | Copyright 2000-2020 The OpenSSL Project Authors. All Rights Reserved. |
e2f92610 RS |
93 | |
94 | Licensed under the OpenSSL license (the "License"). You may not use | |
95 | this file except in compliance with the License. You can obtain a copy | |
96 | in the file LICENSE in the source distribution or at | |
97 | L<https://www.openssl.org/source/license.html>. | |
98 | ||
99 | =cut |