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DEC: make sure all polynomials are shifted [-q/2, q/2]

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hasufell 2014-06-01 20:15:51 +02:00
parent 87c8d9a7d5
commit 9b8b7e9129
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GPG Key ID: 220CD1C5BDEED020
1 changed files with 23 additions and 3 deletions
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26
src/decrypt.c
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@ -47,7 +47,10 @@ ntru_decrypt_poly(
fmpz_poly_t out_bin, fmpz_poly_t out_bin,
ntru_context *ctx) ntru_context *ctx)
{ {
fmpz_poly_t a; fmpz_poly_t a,
priv_key_tmp,
priv_key_inv_tmp,
encr_msg_tmp;
if (!encr_msg || !priv_key || !priv_key_inv || !out_bin || !ctx) if (!encr_msg || !priv_key || !priv_key_inv || !out_bin || !ctx)
return false; return false;
@ -55,12 +58,29 @@ ntru_decrypt_poly(
fmpz_poly_init(a); fmpz_poly_init(a);
fmpz_poly_zero(a); fmpz_poly_zero(a);
poly_starmultiply(priv_key, encr_msg, a, ctx, ctx->q); /*
* make sure all are shifted to
* [-q/2, q/2]
*/
fmpz_poly_init(priv_key_tmp);
fmpz_poly_init(priv_key_inv_tmp);
fmpz_poly_init(encr_msg_tmp);
fmpz_poly_set(priv_key_tmp, priv_key);
fmpz_poly_set(priv_key_inv_tmp, priv_key_inv);
fmpz_poly_set(encr_msg_tmp, encr_msg);
fmpz_poly_mod(priv_key_tmp, ctx->q);
fmpz_poly_mod(priv_key_inv_tmp, ctx->q);
fmpz_poly_mod(encr_msg_tmp, ctx->q);
poly_starmultiply(priv_key_tmp, encr_msg_tmp, a, ctx, ctx->q);
fmpz_poly_mod(a, ctx->q); fmpz_poly_mod(a, ctx->q);
poly_starmultiply(a, priv_key_inv, out_bin, ctx, ctx->p); poly_starmultiply(a, priv_key_inv_tmp, out_bin, ctx, ctx->p);
fmpz_poly_mod(out_bin, ctx->p); fmpz_poly_mod(out_bin, ctx->p);
fmpz_poly_clear(a); fmpz_poly_clear(a);
fmpz_poly_clear(priv_key_tmp);
fmpz_poly_clear(priv_key_inv_tmp);
fmpz_poly_clear(encr_msg_tmp);
return true; return true;
} }