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1 | =pod | ||
2 | |||
3 | =head1 NAME | ||
4 | |||
5 | EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key algorithm shared secret. | ||
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) | ||
60 | /* Error occurred */ | ||
61 | if (EVP_PKEY_derive_init(ctx) <= 0) | ||
62 | /* Error */ | ||
63 | if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0) | ||
64 | /* Error */ | ||
65 | |||
66 | /* Determine buffer length */ | ||
67 | if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0) | ||
68 | /* Error */ | ||
69 | |||
70 | skey = OPENSSL_malloc(skeylen); | ||
71 | |||
72 | if (!skey) | ||
73 | /* malloc failure */ | ||
74 | |||
75 | if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0) | ||
76 | /* Error */ | ||
77 | |||
78 | /* Shared secret is skey bytes written to buffer skey */ | ||
79 | |||
80 | =head1 SEE ALSO | ||
81 | |||
82 | L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>, | ||
83 | L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>, | ||
84 | L<EVP_PKEY_decrypt(3)|EVP_PKEY_decrypt(3)>, | ||
85 | L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>, | ||
86 | L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>, | ||
87 | L<EVP_PKEY_verifyrecover(3)|EVP_PKEY_verifyrecover(3)>, | ||
88 | |||
89 | =head1 HISTORY | ||
90 | |||
91 | These functions were first added to OpenSSL 1.0.0. | ||
92 | |||
93 | =cut | ||