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c0e0984f12
Because the algorithm to use is decided already when creating an EVP_PKEY_CTX regardless of how it was created, it turns out that it's unnecessary to provide the KEYEXCH method explicitly, and rather always have it be fetched implicitly. This means fewer changes for applications that want to use new key exchange algorithms / implementations. Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from https://github.com/openssl/openssl/pull/10305)
111 lines
3.2 KiB
Plaintext
111 lines
3.2 KiB
Plaintext
=pod
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=head1 NAME
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EVP_PKEY_derive_init, 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_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 implict fetches.
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EVP_PKEY_derive_set_peer() sets the peer key: this will normally
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be a public key.
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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() or EVP_PKEY_derive_init_ex() 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_ex(), 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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These functions were added in OpenSSL 1.0.0. The EVP_PKEY_derive_init_ex()
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function was added in OpenSSL 3.0.
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=head1 COPYRIGHT
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Copyright 2006-2018 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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