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ba702545 DSH |
1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
bb9ad09e | 5 | EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key algorithm shared secret |
ba702545 DSH |
6 | |
7 | =head1 SYNOPSIS | |
8 | ||
9 | #include <openssl/evp.h> | |
10 | ||
11 | int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx); | |
12 | int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer); | |
13 | int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen); | |
14 | ||
15 | =head1 DESCRIPTION | |
16 | ||
17 | The EVP_PKEY_derive_init() function initializes a public key algorithm | |
18 | context using key B<pkey> for shared secret derivation. | |
19 | ||
20 | The EVP_PKEY_derive_set_peer() function sets the peer key: this will normally | |
21 | be a public key. | |
22 | ||
23 | The EVP_PKEY_derive() derives a shared secret using B<ctx>. | |
24 | If B<key> is B<NULL> then the maximum size of the output buffer is written to | |
25 | the B<keylen> parameter. If B<key> is not B<NULL> then before the call the | |
26 | B<keylen> parameter should contain the length of the B<key> buffer, if the call | |
27 | is successful the shared secret is written to B<key> and the amount of data | |
28 | written to B<keylen>. | |
29 | ||
30 | =head1 NOTES | |
31 | ||
32 | After the call to EVP_PKEY_derive_init() algorithm specific control | |
33 | operations can be performed to set any appropriate parameters for the | |
34 | operation. | |
35 | ||
36 | The function EVP_PKEY_derive() can be called more than once on the same | |
37 | context if several operations are performed using the same parameters. | |
38 | ||
39 | =head1 RETURN VALUES | |
40 | ||
41 | EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1 for success and 0 | |
42 | or a negative value for failure. In particular a return value of -2 | |
43 | indicates the operation is not supported by the public key algorithm. | |
44 | ||
45 | =head1 EXAMPLE | |
46 | ||
47 | Derive shared secret (for example DH or EC keys): | |
48 | ||
49 | #include <openssl/evp.h> | |
50 | #include <openssl/rsa.h> | |
51 | ||
52 | EVP_PKEY_CTX *ctx; | |
53 | unsigned char *skey; | |
54 | size_t skeylen; | |
55 | EVP_PKEY *pkey, *peerkey; | |
56 | /* NB: assumes pkey, peerkey have been already set up */ | |
57 | ||
58 | ctx = EVP_PKEY_CTX_new(pkey); | |
59 | if (!ctx) | |
2947af32 | 60 | /* Error occurred */ |
ba702545 | 61 | if (EVP_PKEY_derive_init(ctx) <= 0) |
2947af32 | 62 | /* Error */ |
ba702545 | 63 | if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0) |
2947af32 | 64 | /* Error */ |
ba702545 DSH |
65 | |
66 | /* Determine buffer length */ | |
67 | if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0) | |
2947af32 | 68 | /* Error */ |
ba702545 DSH |
69 | |
70 | skey = OPENSSL_malloc(skeylen); | |
71 | ||
72 | if (!skey) | |
2947af32 | 73 | /* malloc failure */ |
1bc74519 | 74 | |
ba702545 | 75 | if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0) |
2947af32 | 76 | /* Error */ |
ba702545 DSH |
77 | |
78 | /* Shared secret is skey bytes written to buffer skey */ | |
79 | ||
80 | =head1 SEE ALSO | |
81 | ||
9b86974e RS |
82 | L<EVP_PKEY_CTX_new(3)>, |
83 | L<EVP_PKEY_encrypt(3)>, | |
84 | L<EVP_PKEY_decrypt(3)>, | |
85 | L<EVP_PKEY_sign(3)>, | |
86 | L<EVP_PKEY_verify(3)>, | |
87 | L<EVP_PKEY_verify_recover(3)>, | |
ba702545 DSH |
88 | |
89 | =head1 HISTORY | |
90 | ||
fb552ac6 | 91 | These functions were first added to OpenSSL 1.0.0. |
ba702545 | 92 | |
e2f92610 RS |
93 | =head1 COPYRIGHT |
94 | ||
95 | Copyright 2006-2016 The OpenSSL Project Authors. All Rights Reserved. | |
96 | ||
97 | Licensed under the OpenSSL license (the "License"). You may not use | |
98 | this file except in compliance with the License. You can obtain a copy | |
99 | in the file LICENSE in the source distribution or at | |
100 | L<https://www.openssl.org/source/license.html>. | |
101 | ||
102 | =cut |