Updated: 2022/Sep/29

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EVP_PKEY_decapsulate(3)             OpenSSL            EVP_PKEY_decapsulate(3)



NAME
       EVP_PKEY_decapsulate_init, EVP_PKEY_decapsulate - Key decapsulation
       using a KEM algorithm with a private key

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/evp.h>

        int EVP_PKEY_decapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
        int EVP_PKEY_decapsulate(EVP_PKEY_CTX *ctx,
                                 unsigned char *unwrapped, size_t *unwrappedlen,
                                 const unsigned char *wrapped, size_t wrappedlen);

DESCRIPTION
       The EVP_PKEY_decapsulate_init() function initializes a private key
       algorithm context ctx for a decapsulation operation and then sets the
       params on the context in the same way as calling
       EVP_PKEY_CTX_set_params(3).  Note that ctx usually is produced using
       EVP_PKEY_CTX_new_from_pkey(3), specifying the private key to use.

       The EVP_PKEY_decapsulate() function performs a private key
       decapsulation operation using ctx. The data to be decapsulated is
       specified using the wrapped and wrappedlen parameters.  If unwrapped is
       NULL then the maximum size of the output secret buffer is written to
       *unwrappedlen. If unwrapped is not NULL and the call is successful then
       the decapsulated secret data is written to unwrapped and the amount of
       data written to *unwrappedlen.

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

RETURN VALUES
       EVP_PKEY_decapsulate_init() and EVP_PKEY_decapsulate() 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 private key
       algorithm.

EXAMPLES
       Decapsulate data using RSA:

        #include <openssl/evp.h>

        /*
         * NB: assumes rsa_priv_key is an RSA private key,
         * and that in, inlen are already set up to contain encapsulated data.
         */

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

        ctx = EVP_PKEY_CTX_new_from_pkey(libctx, rsa_priv_key, NULL);
        if (ctx = NULL)
            /* Error */
        if (EVP_PKEY_decapsulate_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_decapsulate(ctx, NULL, &secretlen, in, inlen) <= 0)
            /* Error */

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

        /* Decapsulated secret data is secretlen bytes long */
        if (EVP_PKEY_decapsulaterctx, secret, &secretlen, in, inlen) <= 0)
            /* Error */

SEE ALSO
       EVP_PKEY_CTX_new_from_pkey(3), EVP_PKEY_encapsulate(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>.



3.0.12                            2023-10-25           EVP_PKEY_decapsulate(3)