NAME

       EVP_PKEY_encapsulate_init, EVP_PKEY_encapsulate - Key encapsulation using a KEM algorithm
       with a public key

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 *wrappedkey, size_t *wrappedkeylen,
                                 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).  Note that ctx is usually is produced using
       EVP_PKEY_CTX_new_from_pkey(3), specifying the public key to use.

       The EVP_PKEY_encapsulate() function performs a public key encapsulation operation using
       ctx.  The symmetric secret generated in genkey can be used as key material.  The
       ciphertext in wrappedkey is its encapsulated form, which can be sent to another party, who
       can use EVP_PKEY_decapsulate(3) to retrieve it using their private key.  If wrappedkey is
       NULL then the maximum size of the output buffer is written to the *wrappedkeylen parameter
       unless wrappedkeylen is NULL and the maximum size of the generated key buffer is written
       to *genkeylen unless genkeylen is NULL.  If wrappedkey 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 wrappedkey and
       its size is written to *wrappedkeylen.

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

HISTORY

       These functions were added in OpenSSL 3.0.

COPYRIGHT

       Copyright 2020-2023 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>.