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.IX Title "EVP_PKEY_DECAPSULATE 3ssl"
.TH EVP_PKEY_DECAPSULATE 3ssl 2024-10-23 3.4.0 OpenSSL
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH NAME
EVP_PKEY_decapsulate_init, EVP_PKEY_auth_decapsulate_init, EVP_PKEY_decapsulate
\&\- Key decapsulation using a KEM algorithm with a private key
.SH SYNOPSIS
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& int EVP_PKEY_decapsulate_init(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
\& int EVP_PKEY_auth_decapsulate_init(EVP_PKEY_CTX *ctx, EVP_PKEY *authpub,
\&                                   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);
.Ve
.SH DESCRIPTION
.IX Header "DESCRIPTION"
The \fBEVP_PKEY_decapsulate_init()\fR function initializes a private key algorithm
context \fIctx\fR for a decapsulation operation and then sets the \fIparams\fR
on the context in the same way as calling \fBEVP_PKEY_CTX_set_params\fR\|(3).
Note that \fIctx\fR usually is produced using \fBEVP_PKEY_CTX_new_from_pkey\fR\|(3),
specifying the private key to use.
.PP
The \fBEVP_PKEY_auth_decapsulate_init()\fR function is similar to
\&\fBEVP_PKEY_decapsulate_init()\fR but also passes an \fIauthpub\fR authentication public
key that is used during decapsulation.
.PP
The \fBEVP_PKEY_decapsulate()\fR function performs a private key decapsulation
operation using \fIctx\fR. The data to be decapsulated is specified using the
\&\fIwrapped\fR and \fIwrappedlen\fR parameters.
If \fIunwrapped\fR is NULL then the size of the output secret buffer
is written to \fI*unwrappedlen\fR. If \fIunwrapped\fR is not NULL and the
call is successful then the decapsulated secret data is written to \fIunwrapped\fR
and the amount of data written to \fI*unwrappedlen\fR.  Note that, if \fIunwrappedlen\fR
is not NULL in this call, the value it points to must be initialised to the length of
\&\fIunwrapped\fR, so that the call can validate it is of sufficient size to hold the
result of the operation.
.SH NOTES
.IX Header "NOTES"
After the call to \fBEVP_PKEY_decapsulate_init()\fR algorithm-specific parameters
for the operation may be set or modified using \fBEVP_PKEY_CTX_set_params\fR\|(3).
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBEVP_PKEY_decapsulate_init()\fR, \fBEVP_PKEY_auth_decapsulate_init()\fR and
\&\fBEVP_PKEY_decapsulate()\fR 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.
.SH EXAMPLES
.IX Header "EXAMPLES"
Decapsulate data using RSA:
.PP
.Vb 1
\& #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 \*(AqRSASVE\*(Aq 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_decapsulate(ctx, secret, &secretlen, in, inlen) <= 0)
\&     /* Error */
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new_from_pkey\fR\|(3),
\&\fBEVP_PKEY_encapsulate\fR\|(3),
\&\fBEVP_KEM\-RSA\fR\|(7), \fBEVP_KEM\-X25519\fR\|(7), \fBEVP_KEM\-EC\fR\|(7)
.SH HISTORY
.IX Header "HISTORY"
The functions \fBEVP_PKEY_decapsulate_init()\fR and \fBEVP_PKEY_decapsulate()\fR were added
in OpenSSL 3.0.
.PP
The function \fBEVP_PKEY_auth_decapsulate_init()\fR was added in OpenSSL 3.2.
.SH COPYRIGHT
.IX Header "COPYRIGHT"
Copyright 2020\-2024 The OpenSSL Project Authors. All Rights Reserved.
.PP
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>.