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.\" ========================================================================
.\"
.IX Title "EVP_PKEY_DECRYPT 3"
.TH EVP_PKEY_DECRYPT 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
EVP_PKEY_decrypt_init, EVP_PKEY_decrypt \- decrypt using a public key algorithm
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& int EVP_PKEY_decrypt_init(EVP_PKEY_CTX *ctx);
\& int EVP_PKEY_decrypt(EVP_PKEY_CTX *ctx,
\&                      unsigned char *out, size_t *outlen,
\&                      const unsigned char *in, size_t inlen);
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \fBEVP_PKEY_decrypt_init()\fR function initializes a public key algorithm
context using key \fBpkey\fR for a decryption operation.
.PP
The \fBEVP_PKEY_decrypt()\fR function performs a public key decryption operation
using \fBctx\fR. The data to be decrypted is specified using the \fBin\fR and
\&\fBinlen\fR parameters. If \fBout\fR is \fB\s-1NULL\s0\fR then the maximum size of the output
buffer is written to the \fBoutlen\fR parameter. If \fBout\fR is not \fB\s-1NULL\s0\fR then
before the call the \fBoutlen\fR parameter should contain the length of the
\&\fBout\fR buffer, if the call is successful the decrypted data is written to
\&\fBout\fR and the amount of data written to \fBoutlen\fR.
.SH "NOTES"
.IX Header "NOTES"
After the call to \fBEVP_PKEY_decrypt_init()\fR algorithm specific control
operations can be performed to set any appropriate parameters for the
operation.
.PP
The function \fBEVP_PKEY_decrypt()\fR can be called more than once on the same
context if several operations are performed using the same parameters.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBEVP_PKEY_decrypt_init()\fR and \fBEVP_PKEY_decrypt()\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 public key algorithm.
.SH "EXAMPLES"
.IX Header "EXAMPLES"
Decrypt data using \s-1OAEP\s0 (for \s-1RSA\s0 keys):
.PP
.Vb 2
\& #include <openssl/evp.h>
\& #include <openssl/rsa.h>
\&
\& EVP_PKEY_CTX *ctx;
\& ENGINE *eng;
\& unsigned char *out, *in;
\& size_t outlen, inlen;
\& EVP_PKEY *key;
\&
\& /*
\&  * NB: assumes key, eng, in, inlen are already set up
\&  * and that key is an RSA private key
\&  */
\& ctx = EVP_PKEY_CTX_new(key, eng);
\& if (!ctx)
\&     /* Error occurred */
\& if (EVP_PKEY_decrypt_init(ctx) <= 0)
\&     /* Error */
\& if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_OAEP_PADDING) <= 0)
\&     /* Error */
\&
\& /* Determine buffer length */
\& if (EVP_PKEY_decrypt(ctx, NULL, &outlen, in, inlen) <= 0)
\&     /* Error */
\&
\& out = OPENSSL_malloc(outlen);
\&
\& if (!out)
\&     /* malloc failure */
\&
\& if (EVP_PKEY_decrypt(ctx, out, &outlen, in, inlen) <= 0)
\&     /* Error */
\&
\& /* Decrypted data is outlen bytes written to buffer out */
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBEVP_PKEY_CTX_new\fR\|(3),
\&\fBEVP_PKEY_encrypt\fR\|(3),
\&\fBEVP_PKEY_sign\fR\|(3),
\&\fBEVP_PKEY_verify\fR\|(3),
\&\fBEVP_PKEY_verify_recover\fR\|(3),
\&\fBEVP_PKEY_derive\fR\|(3)
.SH "HISTORY"
.IX Header "HISTORY"
These functions were added in OpenSSL 1.0.0.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2006\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (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>.