NAME

       EVP_PKEY_encapsulate_init, EVP_PKEY_encapsulate - Key encapsulation using a public key
       algorithm

SYNOPSIS

        #include <openssl/evp.h>

        int EVP_PKEY_encapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
        int EVP_PKEY_encapsulate(EVP_PKEY_CTX *ctx,
                                 unsigned char *out, size_t *outlen,
                                 unsigned char *genkey, size_t *genkeylen);

DESCRIPTION

       The EVP_PKEY_encapsulate_init() function initializes a public key algorithm context ctx
       for an encapsulation operation and then sets the params on the context in the same way as
       calling EVP_PKEY_CTX_set_params(3).

       The EVP_PKEY_encapsulate() function performs a public key encapsulation operation using
       ctx with the name name.  If out is NULL then the maximum size of the output buffer is
       written to the *outlen parameter and the maximum size of the generated key buffer is
       written to *genkeylen. If out is not NULL and the call is successful then the internally
       generated key is written to genkey and its size is written to *genkeylen. The encapsulated
       version of the generated key is written to out and its size is written to *outlen.

NOTES

       After the call to EVP_PKEY_encapsulate_init() algorithm specific parameters for the
       operation may be set or modified using EVP_PKEY_CTX_set_params(3).

RETURN VALUES

       EVP_PKEY_encapsulate_init() and EVP_PKEY_encapsulate() 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

       Encapsulate an RSASVE key (for RSA keys).

        #include <openssl/evp.h>

        /*
         * NB: assumes rsa_pub_key is an public key of another party.
         */

        EVP_PKEY_CTX *ctx = NULL;
        size_t secretlen = 0, outlen = 0;
        unsigned char *out = NULL, *secret = NULL;

        ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_pub_key, NULL);
        if (ctx = NULL)
            /* Error */
        if (EVP_PKEY_encapsulate_init(ctx, NULL) <= 0)
            /* Error */

        /* Set the mode - only 'RSASVE' is currently supported */
         if (EVP_PKEY_CTX_set_kem_op(ctx, "RSASVE") <= 0)
            /* Error */
        /* Determine buffer length */
        if (EVP_PKEY_encapsulate(ctx, NULL, &outlen, NULL, &secretlen) <= 0)
            /* Error */

        out = OPENSSL_malloc(outlen);
        secret = OPENSSL_malloc(secretlen);
        if (out == NULL || secret == NULL)
            /* malloc failure */

        /*
         * The generated 'secret' can be used as key material.
         * The encapsulated 'out' can be sent to another party who can
         * decapsulate it using their private key to retrieve the 'secret'.
         */
        if (EVP_PKEY_encapsulate(ctx, out, &outlen, secret, &secretlen) <= 0)
            /* Error */

SEE ALSO

       EVP_PKEY_CTX_new(3), EVP_PKEY_decapsulate(3), EVP_KEM-RSA(7),

HISTORY

       These functions were added in OpenSSL 3.0.

COPYRIGHT

       Copyright 2020-2021 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>.