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125 lines
3.8 KiB
Plaintext
125 lines
3.8 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY_derive_init, EVP_PKEY_derive_init_ex,
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EVP_PKEY_derive_set_peer_ex, EVP_PKEY_derive_set_peer, EVP_PKEY_derive
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- derive public key algorithm shared secret
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
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int EVP_PKEY_derive_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
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int EVP_PKEY_derive_set_peer_ex(EVP_PKEY_CTX *ctx, EVP_PKEY *peer,
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int validate_peer);
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int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
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int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);
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=head1 DESCRIPTION
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EVP_PKEY_derive_init() initializes a public key algorithm context I<ctx> for
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shared secret derivation using the algorithm given when the context was created
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using L<EVP_PKEY_CTX_new(3)> or variants thereof. The algorithm is used to
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fetch a B<EVP_KEYEXCH> method implicitly, see L<provider(7)/Implicit fetch> for
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more information about implicit fetches.
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EVP_PKEY_derive_init_ex() is the same as EVP_PKEY_derive_init() but additionally
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sets the passed parameters I<params> on the context before returning.
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EVP_PKEY_derive_set_peer_ex() sets the peer key: this will normally
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be a public key. The I<validate_peer> will validate the public key if this value
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is non zero.
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EVP_PKEY_derive_set_peer() is similar to EVP_PKEY_derive_set_peer_ex() with
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I<validate_peer> set to 1.
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EVP_PKEY_derive() derives a shared secret using I<ctx>.
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If I<key> is NULL then the maximum size of the output buffer is written to the
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I<keylen> parameter. If I<key> is not NULL then before the call the I<keylen>
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parameter should contain the length of the I<key> buffer, if the call is
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successful the shared secret is written to I<key> and the amount of data
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written to I<keylen>.
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=head1 NOTES
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After the call to EVP_PKEY_derive_init(), algorithm
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specific control operations can be performed to set any appropriate parameters
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for the operation.
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The function EVP_PKEY_derive() can be called more than once on the same
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context if several operations are performed using the same parameters.
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=head1 RETURN VALUES
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EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1
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for success and 0 or a negative value for failure.
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In particular a return value of -2 indicates the operation is not supported by
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the public key algorithm.
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=head1 EXAMPLES
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Derive shared secret (for example DH or EC keys):
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#include <openssl/evp.h>
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#include <openssl/rsa.h>
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EVP_PKEY_CTX *ctx;
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ENGINE *eng;
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unsigned char *skey;
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size_t skeylen;
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EVP_PKEY *pkey, *peerkey;
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/* NB: assumes pkey, eng, peerkey have been already set up */
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ctx = EVP_PKEY_CTX_new(pkey, eng);
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if (!ctx)
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/* Error occurred */
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if (EVP_PKEY_derive_init(ctx) <= 0)
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/* Error */
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if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
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/* Error */
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/* Determine buffer length */
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if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
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/* Error */
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skey = OPENSSL_malloc(skeylen);
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if (!skey)
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/* malloc failure */
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if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
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/* Error */
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/* Shared secret is skey bytes written to buffer skey */
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=head1 SEE ALSO
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L<EVP_PKEY_CTX_new(3)>,
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L<EVP_PKEY_encrypt(3)>,
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L<EVP_PKEY_decrypt(3)>,
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L<EVP_PKEY_sign(3)>,
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L<EVP_PKEY_verify(3)>,
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L<EVP_PKEY_verify_recover(3)>,
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L<EVP_KEYEXCH_fetch(3)>
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=head1 HISTORY
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The EVP_PKEY_derive_init(), EVP_PKEY_derive_set_peer() and EVP_PKEY_derive()
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functions were originally added in OpenSSL 1.0.0.
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The EVP_PKEY_derive_init_ex() and EVP_PKEY_derive_set_peer_ex() functions were
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added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2006-2022 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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