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.\" ========================================================================
.\"
.IX Title "EVP_PKEY_DECAPSULATE 3SSL"
.TH EVP_PKEY_DECAPSULATE 3SSL "2023-10-23" "3.0.11" "OpenSSL"
.\" For nroff, turn off justification. Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_PKEY_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_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_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 \s-1NULL\s0 then the maximum size of the output secret buffer
is written to \fI*unwrappedlen\fR. If \fIunwrapped\fR is not \s-1NULL\s0 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.
.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 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 \s-1RSA:\s0
.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_decapsulaterctx, 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),
\&\s-1\fBEVP_KEM\-RSA\s0\fR\|(7),
.SH "HISTORY"
.IX Header "HISTORY"
These functions were added in OpenSSL 3.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2020\-2023 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the Apache License 2.0 (the \*(L"License\*(R"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.
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