EVP_PKEY_DECAPSULATE(3SSL) OpenSSL EVP_PKEY_DECAPSULATE(3SSL)
NAME
EVP_PKEY_decapsulate_init, EVP_PKEY_decapsulate - Key decapsulation
using a private key algorithm
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 *secret, size_t *secretlen,
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).
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 secret is
NULL then the maximum size of the output secret buffer is written to
the *secretlen parameter. If secret is not NULL and the call is
successful then the decapsulated secret data is written to secret and
the amount of data written to secretlen.
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(3), EVP_PKEY_encapsulate(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>.
3.0.2 2026-04-07 EVP_PKEY_DECAPSULATE(3SSL)
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