| 1 | =pod
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| 2 |
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| 3 | =head1 NAME
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| 4 |
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| 5 | EVP_PKEY_derive_init, EVP_PKEY_derive_init_ex,
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| 6 | EVP_PKEY_derive_set_peer_ex, EVP_PKEY_derive_set_peer, EVP_PKEY_derive
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| 7 | - derive public key algorithm shared secret
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| 8 |
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| 9 | =head1 SYNOPSIS
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| 10 |
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| 11 | #include <openssl/evp.h>
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| 12 |
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| 13 | int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
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| 14 | int EVP_PKEY_derive_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
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| 15 | int EVP_PKEY_derive_set_peer_ex(EVP_PKEY_CTX *ctx, EVP_PKEY *peer,
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| 16 | int validate_peer);
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| 17 | int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
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| 18 | int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);
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| 19 |
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| 20 | =head1 DESCRIPTION
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| 21 |
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| 22 | EVP_PKEY_derive_init() initializes a public key algorithm context I<ctx> for
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| 23 | shared secret derivation using the algorithm given when the context was created
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| 24 | using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to
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| 25 | fetch a B<EVP_KEYEXCH> method implicitly, see L<provider(7)/Implicit fetch> for
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| 26 | more information about implicit fetches.
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| 27 |
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| 28 | EVP_PKEY_derive_init_ex() is the same as EVP_PKEY_derive_init() but additionally
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| 29 | sets the passed parameters I<params> on the context before returning.
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| 30 |
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| 31 | EVP_PKEY_derive_set_peer_ex() sets the peer key: this will normally
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| 32 | be a public key. The I<validate_peer> will validate the public key if this value
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| 33 | is non zero.
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| 34 |
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| 35 | EVP_PKEY_derive_set_peer() is similar to EVP_PKEY_derive_set_peer_ex() with
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| 36 | I<validate_peer> set to 1.
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| 37 |
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| 38 | EVP_PKEY_derive() derives a shared secret using I<ctx>.
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| 39 | If I<key> is NULL then the maximum size of the output buffer is written to the
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| 40 | I<keylen> parameter. If I<key> is not NULL then before the call the I<keylen>
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| 41 | parameter should contain the length of the I<key> buffer, if the call is
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| 42 | successful the shared secret is written to I<key> and the amount of data
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| 43 | written to I<keylen>.
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| 44 |
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| 45 | =head1 NOTES
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| 46 |
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| 47 | After the call to EVP_PKEY_derive_init(), algorithm
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| 48 | specific control operations can be performed to set any appropriate parameters
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| 49 | for the operation.
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| 50 |
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| 51 | The function EVP_PKEY_derive() can be called more than once on the same
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| 52 | context if several operations are performed using the same parameters.
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| 53 |
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| 54 | =head1 RETURN VALUES
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| 55 |
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| 56 | EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1
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| 57 | for success and 0 or a negative value for failure.
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| 58 | In particular a return value of -2 indicates the operation is not supported by
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| 59 | the public key algorithm.
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| 60 |
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| 61 | =head1 EXAMPLES
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| 62 |
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| 63 | Derive shared secret (for example DH or EC keys):
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| 64 |
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| 65 | #include <openssl/evp.h>
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| 66 | #include <openssl/rsa.h>
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| 67 |
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| 68 | EVP_PKEY_CTX *ctx;
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| 69 | ENGINE *eng;
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| 70 | unsigned char *skey;
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| 71 | size_t skeylen;
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| 72 | EVP_PKEY *pkey, *peerkey;
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| 73 | /* NB: assumes pkey, eng, peerkey have been already set up */
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| 74 |
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| 75 | ctx = EVP_PKEY_CTX_new(pkey, eng);
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| 76 | if (!ctx)
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| 77 | /* Error occurred */
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| 78 | if (EVP_PKEY_derive_init(ctx) <= 0)
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| 79 | /* Error */
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| 80 | if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
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| 81 | /* Error */
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| 82 |
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| 83 | /* Determine buffer length */
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| 84 | if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
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| 85 | /* Error */
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| 86 |
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| 87 | skey = OPENSSL_malloc(skeylen);
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| 88 |
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| 89 | if (!skey)
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| 90 | /* malloc failure */
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| 91 |
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| 92 | if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
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| 93 | /* Error */
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| 94 |
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| 95 | /* Shared secret is skey bytes written to buffer skey */
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| 96 |
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| 97 | =head1 SEE ALSO
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| 98 |
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| 99 | L<EVP_PKEY_CTX_new(3)>,
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| 100 | L<EVP_PKEY_encrypt(3)>,
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| 101 | L<EVP_PKEY_decrypt(3)>,
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| 102 | L<EVP_PKEY_sign(3)>,
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| 103 | L<EVP_PKEY_verify(3)>,
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| 104 | L<EVP_PKEY_verify_recover(3)>,
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| 105 | L<EVP_KEYEXCH_fetch(3)>
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| 106 |
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| 107 | =head1 HISTORY
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| 108 |
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| 109 | The EVP_PKEY_derive_init(), EVP_PKEY_derive_set_peer() and EVP_PKEY_derive()
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| 110 | functions were originally added in OpenSSL 1.0.0.
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| 111 |
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| 112 | The EVP_PKEY_derive_init_ex() and EVP_PKEY_derive_set_peer_ex() functions were
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| 113 | added in OpenSSL 3.0.
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| 114 |
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| 115 | =head1 COPYRIGHT
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| 116 |
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| 117 | Copyright 2006-2022 The OpenSSL Project Authors. All Rights Reserved.
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| 118 |
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| 119 | Licensed under the Apache License 2.0 (the "License"). You may not use
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| 120 | this file except in compliance with the License. You can obtain a copy
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| 121 | in the file LICENSE in the source distribution or at
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| 122 | L<https://www.openssl.org/source/license.html>.
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| 123 |
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| 124 | =cut
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