cda774223d
And update find-doc-nits to complain if "=head1 EXAMPLE" is found. Reviewed-by: Richard Levitte <levitte@openssl.org> Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com> (Merged from https://github.com/openssl/openssl/pull/9602)
119 lines
3.6 KiB
Text
119 lines
3.6 KiB
Text
=pod
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=head1 NAME
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EVP_PKEY_derive_init, EVP_PKEY_derive_init_ex, EVP_PKEY_derive_set_peer,
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EVP_PKEY_derive - 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_ex(EVP_PKEY_CTX *ctx, EVP_KEYEXCH *exchange);
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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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The EVP_PKEY_derive_init_ex() function initializes a public key algorithm
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context for shared secret derivation using the key exchange algorithm
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B<exchange>.
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The key exchange algorithm B<exchange> should be fetched using a call to
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L<EVP_KEYEXCH_fetch(3)>.
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The EVP_PKEY object associated with B<ctx> must be compatible with that
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algorithm.
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B<exchange> may be NULL in which case the EVP_KEYEXCH algorithm is fetched
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implicitly based on the type of EVP_PKEY associated with B<ctx>.
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See L<EVP_KEYEXCH_fetch(3)> for more information about implict fetches.
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The EVP_PKEY_derive_init() function is the same as EVP_PKEY_derive() except that
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the EVP_KEYEXCH algorithm is always implicitly fetched.
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The EVP_PKEY_derive_set_peer() function sets the peer key: this will normally
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be a public key.
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The EVP_PKEY_derive() derives a shared secret using B<ctx>.
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If B<key> is B<NULL> then the maximum size of the output buffer is written to
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the B<keylen> parameter. If B<key> is not B<NULL> then before the call the
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B<keylen> parameter should contain the length of the B<key> buffer, if the call
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is successful the shared secret is written to B<key> and the amount of data
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written to B<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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