NAME

       EVP_PKEY_encapsulate_init, EVP_PKEY_auth_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_auth_encapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpriv,
                                          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_auth_encapsulate_init() function is similar to EVP_PKEY_encapsulate_init() but also passes
       an authpriv authentication private key that is used during encapsulation.

       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.  Note that if wrappedlen is not NULL, then the value it points to must initially hold the
       size of the  unwrapped buffer so that its size can be validated by the call, ensuring it is large enough
       to hold the result written to wrapped.

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(), EVP_PKEY_auth_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), EVP_KEM-X25519(7), EVP_KEM-EC(7)

HISTORY

       These functions EVP_PKEY_encapsulate_init() and EVP_PKEY_encapsulate() were added in OpenSSL 3.0.  The
       function EVP_PKEY_auth_encapsulate_init() was added in OpenSSL 3.2.

COPYRIGHT

       Copyright 2020-2024 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>.

3.4.1                                              2025-04-03                         EVP_PKEY_ENCAPSULATE(3SSL)