b053658f95
Multiplication in GF(128) is required by the AES-XEX mode for computing X in the XEX formula from https://en.wikipedia.org/wiki/Disk_encryption_theory#Xor-encrypt-xor_.28XEX.29
79 lines
2.7 KiB
C
79 lines
2.7 KiB
C
/*
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* GF(2^128) multiplication functions
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*
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* Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
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* SPDX-License-Identifier: Apache-2.0
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may
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* not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* This file is part of mbed TLS (https://tls.mbed.org)
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*/
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#include <stdint.h>
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#include "mbedtls/gf128mul.h"
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/* Endianess with 64 bits values */
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#ifndef GET_UINT64_LE
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#define GET_UINT64_LE(n,b,i) \
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{ \
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(n) = ( (uint64_t) (b)[(i) + 7] << 56 ) \
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| ( (uint64_t) (b)[(i) + 6] << 48 ) \
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| ( (uint64_t) (b)[(i) + 5] << 40 ) \
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| ( (uint64_t) (b)[(i) + 4] << 32 ) \
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| ( (uint64_t) (b)[(i) + 3] << 24 ) \
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| ( (uint64_t) (b)[(i) + 2] << 16 ) \
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| ( (uint64_t) (b)[(i) + 1] << 8 ) \
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| ( (uint64_t) (b)[(i) ] ); \
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}
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#endif
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#ifndef PUT_UINT64_LE
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#define PUT_UINT64_LE(n,b,i) \
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{ \
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(b)[(i) + 7] = (unsigned char) ( (n) >> 56 ); \
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(b)[(i) + 6] = (unsigned char) ( (n) >> 48 ); \
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(b)[(i) + 5] = (unsigned char) ( (n) >> 40 ); \
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(b)[(i) + 4] = (unsigned char) ( (n) >> 32 ); \
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(b)[(i) + 3] = (unsigned char) ( (n) >> 24 ); \
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(b)[(i) + 2] = (unsigned char) ( (n) >> 16 ); \
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(b)[(i) + 1] = (unsigned char) ( (n) >> 8 ); \
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(b)[(i) ] = (unsigned char) ( (n) ); \
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}
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#endif
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/* Jump table for not having ifs */
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static const uint16_t gf128mul_table_bbe[2] = { 0x00, 0x87 };
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/*
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* This function multiply a field element by x, by x^4 and by x^8
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* in the polynomial field representation. It uses 64-bit word operations
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* to gain speed but compensates for machine endianess and hence works
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* correctly on both styles of machine.
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*/
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void mbedtls_gf128mul_x_ble(mbedtls_be128 r, const mbedtls_be128 x)
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{
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uint64_t a, b, ra, rb;
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GET_UINT64_LE(a, x, 0);
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GET_UINT64_LE(b, x, 8);
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ra = (a << 1) ^ gf128mul_table_bbe[b >> 63];
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rb = (a >> 63) | (b << 1);
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PUT_UINT64_LE(ra, r, 0);
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PUT_UINT64_LE(rb, r, 8);
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}
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