152 lines
3.6 KiB
C
152 lines
3.6 KiB
C
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/*
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* AES (Rijndael) cipher - decrypt
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*
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* Modifications to public domain implementation:
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* - support only 128-bit keys
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* - cleanup
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* - use C pre-processor to make it easier to change S table access
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* - added option (AES_SMALL_TABLES) for reducing code size by about 8 kB at
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* cost of reduced throughput (quite small difference on Pentium 4,
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* 10-25% when using -O1 or -O2 optimization)
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*
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* Copyright (c) 2003-2005, Jouni Malinen <j@w1.fi>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* Alternatively, this software may be distributed under the terms of BSD
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* license.
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*
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* See README and COPYING for more details.
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*/
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#include "includes.h"
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#include "common.h"
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#include "crypto.h"
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#include "aes_i.h"
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/**
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* Expand the cipher key into the decryption key schedule.
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*
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* @return the number of rounds for the given cipher key size.
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*/
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void rijndaelKeySetupDec(u32 rk[/*44*/], const u8 cipherKey[])
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{
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int Nr = 10, i, j;
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u32 temp;
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/* expand the cipher key: */
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rijndaelKeySetupEnc(rk, cipherKey);
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/* invert the order of the round keys: */
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for (i = 0, j = 4*Nr; i < j; i += 4, j -= 4) {
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temp = rk[i ]; rk[i ] = rk[j ]; rk[j ] = temp;
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temp = rk[i + 1]; rk[i + 1] = rk[j + 1]; rk[j + 1] = temp;
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temp = rk[i + 2]; rk[i + 2] = rk[j + 2]; rk[j + 2] = temp;
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temp = rk[i + 3]; rk[i + 3] = rk[j + 3]; rk[j + 3] = temp;
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}
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/* apply the inverse MixColumn transform to all round keys but the
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* first and the last: */
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for (i = 1; i < Nr; i++) {
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rk += 4;
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for (j = 0; j < 4; j++) {
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rk[j] = TD0_(TE4((rk[j] >> 24) )) ^
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TD1_(TE4((rk[j] >> 16) & 0xff)) ^
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TD2_(TE4((rk[j] >> 8) & 0xff)) ^
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TD3_(TE4((rk[j] ) & 0xff));
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}
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}
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}
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void * aes_decrypt_init(const u8 *key, size_t len)
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{
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u32 *rk;
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if (len != 16)
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return NULL;
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rk = os_malloc(AES_PRIV_SIZE);
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if (rk == NULL)
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return NULL;
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rijndaelKeySetupDec(rk, key);
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return rk;
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}
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static void rijndaelDecrypt(const u32 rk[/*44*/], const u8 ct[16], u8 pt[16])
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{
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u32 s0, s1, s2, s3, t0, t1, t2, t3;
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const int Nr = 10;
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#ifndef FULL_UNROLL
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int r;
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#endif /* ?FULL_UNROLL */
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/*
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* map byte array block to cipher state
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* and add initial round key:
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*/
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s0 = GETU32(ct ) ^ rk[0];
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s1 = GETU32(ct + 4) ^ rk[1];
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s2 = GETU32(ct + 8) ^ rk[2];
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s3 = GETU32(ct + 12) ^ rk[3];
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#define ROUND(i,d,s) \
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d##0 = TD0(s##0) ^ TD1(s##3) ^ TD2(s##2) ^ TD3(s##1) ^ rk[4 * i]; \
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d##1 = TD0(s##1) ^ TD1(s##0) ^ TD2(s##3) ^ TD3(s##2) ^ rk[4 * i + 1]; \
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d##2 = TD0(s##2) ^ TD1(s##1) ^ TD2(s##0) ^ TD3(s##3) ^ rk[4 * i + 2]; \
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d##3 = TD0(s##3) ^ TD1(s##2) ^ TD2(s##1) ^ TD3(s##0) ^ rk[4 * i + 3]
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#ifdef FULL_UNROLL
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ROUND(1,t,s);
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ROUND(2,s,t);
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ROUND(3,t,s);
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ROUND(4,s,t);
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ROUND(5,t,s);
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ROUND(6,s,t);
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ROUND(7,t,s);
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ROUND(8,s,t);
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ROUND(9,t,s);
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rk += Nr << 2;
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#else /* !FULL_UNROLL */
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/* Nr - 1 full rounds: */
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r = Nr >> 1;
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for (;;) {
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ROUND(1,t,s);
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rk += 8;
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if (--r == 0)
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break;
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ROUND(0,s,t);
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}
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#endif /* ?FULL_UNROLL */
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#undef ROUND
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/*
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* apply last round and
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* map cipher state to byte array block:
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*/
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s0 = TD41(t0) ^ TD42(t3) ^ TD43(t2) ^ TD44(t1) ^ rk[0];
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PUTU32(pt , s0);
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s1 = TD41(t1) ^ TD42(t0) ^ TD43(t3) ^ TD44(t2) ^ rk[1];
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PUTU32(pt + 4, s1);
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s2 = TD41(t2) ^ TD42(t1) ^ TD43(t0) ^ TD44(t3) ^ rk[2];
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PUTU32(pt + 8, s2);
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s3 = TD41(t3) ^ TD42(t2) ^ TD43(t1) ^ TD44(t0) ^ rk[3];
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PUTU32(pt + 12, s3);
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}
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void aes_decrypt(void *ctx, const u8 *crypt, u8 *plain)
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{
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rijndaelDecrypt(ctx, crypt, plain);
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}
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void aes_decrypt_deinit(void *ctx)
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{
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os_memset(ctx, 0, AES_PRIV_SIZE);
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os_free(ctx);
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}
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