pqc/src/decrypt.c

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/*
* Copyright (C) 2014 FH Bielefeld
*
* This file is part of a FH Bielefeld project.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
* MA 02110-1301 USA
*/
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/**
* @file decrypt.c
* This file handles the NTRU decryption
* algorithm.
* @brief NTRU decryption
*/
#include "decrypt.h"
#include <fmpz_poly.h>
#include <fmpz.h>
/**
* Decryption of the given Polynom with the private key, its inverse
* and the fitting ntru_context
*
* @param encr_msg encrypted polynom with maximum length of N from
* the given context
* @param priv_key the polynom containing the private key to decrypt
* the message
* @param priv_key_inv the inverse polynome to the private key
* @param out the result polynom is written in here [out]
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* @param ctx the ntru_context
*/
void ntru_decrypt_poly(
fmpz_poly_t encr_msg,
fmpz_poly_t priv_key,
fmpz_poly_t priv_key_inv,
fmpz_poly_t out,
ntru_context *ctx)
{
fmpz_poly_t a;
fmpz_poly_init(a);
fmpz_poly_zero(a);
poly_starmultiply(priv_key, encr_msg, a, ctx, ctx->q);
fmpz_poly_mod(a, ctx->q);
poly_starmultiply(a, priv_key_inv, out, ctx, ctx->p);
fmpz_poly_mod(out, ctx->p);
}