Updated: 2022/Sep/29

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EVP_PKEY_derive(3)                  OpenSSL                 EVP_PKEY_derive(3)



NAME
       EVP_PKEY_derive_init, EVP_PKEY_derive_init_ex,
       EVP_PKEY_derive_set_peer_ex, EVP_PKEY_derive_set_peer, EVP_PKEY_derive
       - derive public key algorithm shared secret

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/evp.h>

        int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
        int EVP_PKEY_derive_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
        int EVP_PKEY_derive_set_peer_ex(EVP_PKEY_CTX *ctx, EVP_PKEY *peer,
                                        int validate_peer);
        int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
        int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);

DESCRIPTION
       EVP_PKEY_derive_init() initializes a public key algorithm context ctx
       for shared secret derivation using the algorithm given when the context
       was created using EVP_PKEY_CTX_new(3) or variants thereof.  The
       algorithm is used to fetch a EVP_KEYEXCH method implicitly, see
       "Implicit fetch" in provider(7) for more information about implicit
       fetches.

       EVP_PKEY_derive_init_ex() is the same as EVP_PKEY_derive_init() but
       additionally sets the passed parameters params on the context before
       returning.

       EVP_PKEY_derive_set_peer_ex() sets the peer key: this will normally be
       a public key. The validate_peer will validate the public key if this
       value is non zero.

       EVP_PKEY_derive_set_peer() is similar to EVP_PKEY_derive_set_peer_ex()
       with validate_peer set to 1.

       EVP_PKEY_derive() derives a shared secret using ctx.  If key is NULL
       then the maximum size of the output buffer is written to the keylen
       parameter. If key is not NULL then before the call the keylen parameter
       should contain the length of the key buffer, if the call is successful
       the shared secret is written to key and the amount of data written to
       keylen.

NOTES
       After the call to EVP_PKEY_derive_init(), algorithm specific control
       operations can be performed to set any appropriate parameters for the
       operation.

       The function EVP_PKEY_derive() can be called more than once on the same
       context if several operations are performed using the same parameters.

RETURN VALUES
       EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1 for success and 0
       or a negative value for failure.  In particular a return value of -2
       indicates the operation is not supported by the public key algorithm.

EXAMPLES
       Derive shared secret (for example DH or EC keys):

        #include <openssl/evp.h>
        #include <openssl/rsa.h>

        EVP_PKEY_CTX *ctx;
        ENGINE *eng;
        unsigned char *skey;
        size_t skeylen;
        EVP_PKEY *pkey, *peerkey;
        /* NB: assumes pkey, eng, peerkey have been already set up */

        ctx = EVP_PKEY_CTX_new(pkey, eng);
        if (!ctx)
            /* Error occurred */
        if (EVP_PKEY_derive_init(ctx) <= 0)
            /* Error */
        if (EVP_PKEY_derive_set_peer(ctx, peerkey) <= 0)
            /* Error */

        /* Determine buffer length */
        if (EVP_PKEY_derive(ctx, NULL, &skeylen) <= 0)
            /* Error */

        skey = OPENSSL_malloc(skeylen);

        if (!skey)
            /* malloc failure */

        if (EVP_PKEY_derive(ctx, skey, &skeylen) <= 0)
            /* Error */

        /* Shared secret is skey bytes written to buffer skey */

SEE ALSO
       EVP_PKEY_CTX_new(3), EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3),
       EVP_PKEY_sign(3), EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3),
       EVP_KEYEXCH_fetch(3)

HISTORY
       The EVP_PKEY_derive_init(), EVP_PKEY_derive_set_peer() and
       EVP_PKEY_derive() functions were originally added in OpenSSL 1.0.0.

       The EVP_PKEY_derive_init_ex() and EVP_PKEY_derive_set_peer_ex()
       functions were added in OpenSSL 3.0.

COPYRIGHT
       Copyright 2006-2023 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use
       this file except in compliance with the License.  You can obtain a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.



3.0.12                            2023-10-25                EVP_PKEY_derive(3)