5 EVP_PKEY_derive_init, EVP_PKEY_derive_init_ex,
6 EVP_PKEY_derive_set_peer_ex, EVP_PKEY_derive_set_peer, EVP_PKEY_derive
7 - derive public key algorithm shared secret
11 #include <openssl/evp.h>
13 int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
14 int EVP_PKEY_derive_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
15 int EVP_PKEY_derive_set_peer_ex(EVP_PKEY_CTX *ctx, EVP_PKEY *peer,
17 int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
18 int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);
22 EVP_PKEY_derive_init() initializes a public key algorithm context I<ctx> for
23 shared secret derivation using the algorithm given when the context was created
24 using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to
25 fetch a B<EVP_KEYEXCH> method implicitly, see L<provider(7)/Implicit fetch> for
26 more information about implicit fetches.
28 EVP_PKEY_derive_init_ex() is the same as EVP_PKEY_derive_init() but additionally
29 sets the passed parameters I<params> on the context before returning.
31 EVP_PKEY_derive_set_peer_ex() sets the peer key: this will normally
32 be a public key. The I<validate_peer> will validate the public key if this value
35 EVP_PKEY_derive_set_peer() is similiar to EVP_PKEY_derive_set_peer_ex() with
36 I<validate_peer> set to 1.
38 EVP_PKEY_derive() derives a shared secret using I<ctx>.
39 If I<key> is NULL then the maximum size of the output buffer is written to the
40 I<keylen> parameter. If I<key> is not NULL then before the call the I<keylen>
41 parameter should contain the length of the I<key> buffer, if the call is
42 successful the shared secret is written to I<key> and the amount of data
47 After the call to EVP_PKEY_derive_init(), algorithm
48 specific control operations can be performed to set any appropriate parameters
51 The function EVP_PKEY_derive() can be called more than once on the same
52 context if several operations are performed using the same parameters.
56 EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1
57 for success and 0 or a negative value for failure.
58 In particular a return value of -2 indicates the operation is not supported by
59 the public key algorithm.
63 Derive shared secret (for example DH or EC keys):
65 #include <openssl/evp.h>
66 #include <openssl/rsa.h>
72 EVP_PKEY *pkey, *peerkey;
73 /* NB: assumes pkey, eng, peerkey have been already set up */
75 ctx = EVP_PKEY_CTX_new(pkey, eng);
78 if (EVP_PKEY_derive_init(ctx) <= 0)
80 if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
83 /* Determine buffer length */
84 if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
87 skey = OPENSSL_malloc(skeylen);
92 if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
95 /* Shared secret is skey bytes written to buffer skey */
99 L<EVP_PKEY_CTX_new(3)>,
100 L<EVP_PKEY_encrypt(3)>,
101 L<EVP_PKEY_decrypt(3)>,
103 L<EVP_PKEY_verify(3)>,
104 L<EVP_PKEY_verify_recover(3)>,
105 L<EVP_KEYEXCH_fetch(3)>
109 The EVP_PKEY_derive_init(), EVP_PKEY_derive_set_peer() and EVP_PKEY_derive()
110 functions were originally added in OpenSSL 1.0.0.
112 The EVP_PKEY_derive_init_ex() and EVP_PKEY_derive_set_peer_ex() functions were
113 added in OpenSSL 3.0.
117 Copyright 2006-2021 The OpenSSL Project Authors. All Rights Reserved.
119 Licensed under the Apache License 2.0 (the "License"). You may not use
120 this file except in compliance with the License. You can obtain a copy
121 in the file LICENSE in the source distribution or at
122 L<https://www.openssl.org/source/license.html>.