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=pod
=head1 NAME
EVP_PKEY_decrypt_init, EVP_PKEY_decrypt - decrypt using a public key algorithm
=head1 SYNOPSIS
#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);
=head1 DESCRIPTION
The EVP_PKEY_decrypt_init() function initializes a public key algorithm
context using key B<pkey> for a decryption operation.
The EVP_PKEY_decrypt() function performs a public key decryption operation
using B<ctx>. The data to be decrypted is specified using the B<in> and
B<inlen> parameters. If B<out> is B<NULL> then the maximum size of the output
buffer is written to the B<outlen> parameter. If B<out> is not B<NULL> then
before the call the B<outlen> parameter should contain the length of the
B<out> buffer, if the call is successful the decrypted data is written to
B<out> and the amount of data written to B<outlen>.
=head1 NOTES
After the call to EVP_PKEY_decrypt_init() algorithm specific control
operations can be performed to set any appropriate parameters for the
operation.
The function EVP_PKEY_decrypt() can be called more than once on the same
context if several operations are performed using the same parameters.
=head1 RETURN VALUES
EVP_PKEY_decrypt_init() and EVP_PKEY_decrypt() 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.
=head1 EXAMPLE
Decrypt data using OAEP (for RSA keys):
#include <openssl/evp.h>
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
unsigned char *out, *in;
size_t outlen, inlen;
EVP_PKEY *key;
/* NB: assumes key in, inlen are already set up
* and that key is an RSA private key
*/
ctx = EVP_PKEY_CTX_new(key);
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 */
=head1 SEE ALSO
L<EVP_PKEY_CTX_new(3)|EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_encrypt(3)|EVP_PKEY_encrypt(3)>,
L<EVP_PKEY_sign(3)|EVP_PKEY_sign(3)>,
L<EVP_PKEY_verify(3)|EVP_PKEY_verify(3)>,
L<EVP_PKEY_verify_recover(3)|EVP_PKEY_verify_recover(3)>,
L<EVP_PKEY_derive(3)|EVP_PKEY_derive(3)>
=head1 HISTORY
These functions were first added to OpenSSL 1.0.0.
=cut