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       EVP_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key
       algorithm shared secret


        #include <openssl/evp.h>

        int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
        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);


       The EVP_PKEY_derive_init() function initializes a public key algorithm context using key
       pkey for shared secret derivation.

       The EVP_PKEY_derive_set_peer() function sets the peer key: this will normally be a public

       The 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


       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.


       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.


       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 */


       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),


       These functions were added in OpenSSL 1.0.0.


       Copyright 2006-2019 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 <>.