arc4.c

00001 /*
00002  *  An implementation of the ARCFOUR algorithm
00003  *
00004  *  Copyright (C) 2006-2014, ARM Limited, All Rights Reserved
00005  *
00006  *  This file is part of mbed TLS (https://tls.mbed.org)
00007  *
00008  *  This program is free software; you can redistribute it and/or modify
00009  *  it under the terms of the GNU General Public License as published by
00010  *  the Free Software Foundation; either version 2 of the License, or
00011  *  (at your option) any later version.
00012  *
00013  *  This program is distributed in the hope that it will be useful,
00014  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
00015  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00016  *  GNU General Public License for more details.
00017  *
00018  *  You should have received a copy of the GNU General Public License along
00019  *  with this program; if not, write to the Free Software Foundation, Inc.,
00020  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
00021  */
00022 /*
00023  *  The ARCFOUR algorithm was publicly disclosed on 94/09.
00024  *
00025  *  http://groups.google.com/group/sci.crypt/msg/10a300c9d21afca0
00026  */
00027 
00028 #if !defined(POLARSSL_CONFIG_FILE)
00029 #include "polarssl/config.h"
00030 #else
00031 #include POLARSSL_CONFIG_FILE
00032 #endif
00033 
00034 #if defined(POLARSSL_ARC4_C)
00035 
00036 #include "polarssl/arc4.h"
00037 
00038 #include <string.h>
00039 
00040 #if defined(POLARSSL_SELF_TEST)
00041 #if defined(POLARSSL_PLATFORM_C)
00042 #include "polarssl/platform.h"
00043 #else
00044 #include <stdio.h>
00045 #define polarssl_printf printf
00046 #endif /* POLARSSL_PLATFORM_C */
00047 #endif /* POLARSSL_SELF_TEST */
00048 
00049 #if !defined(POLARSSL_ARC4_ALT)
00050 
00051 /* Implementation that should never be optimized out by the compiler */
00052 static void polarssl_zeroize( void *v, size_t n ) {
00053     volatile unsigned char *p = v; while( n-- ) *p++ = 0;
00054 }
00055 
00056 void arc4_init( arc4_context *ctx )
00057 {
00058     memset( ctx, 0, sizeof( arc4_context ) );
00059 }
00060 
00061 void arc4_free( arc4_context *ctx )
00062 {
00063     if( ctx == NULL )
00064         return;
00065 
00066     polarssl_zeroize( ctx, sizeof( arc4_context ) );
00067 }
00068 
00069 /*
00070  * ARC4 key schedule
00071  */
00072 void arc4_setup( arc4_context *ctx, const unsigned char *key,
00073                  unsigned int keylen )
00074 {
00075     int i, j, a;
00076     unsigned int k;
00077     unsigned char *m;
00078 
00079     ctx->x  = 0;
00080     ctx->y  = 0;
00081     m = ctx->m ;
00082 
00083     for( i = 0; i < 256; i++ )
00084         m[i] = (unsigned char) i;
00085 
00086     j = k = 0;
00087 
00088     for( i = 0; i < 256; i++, k++ )
00089     {
00090         if( k >= keylen ) k = 0;
00091 
00092         a = m[i];
00093         j = ( j + a + key[k] ) & 0xFF;
00094         m[i] = m[j];
00095         m[j] = (unsigned char) a;
00096     }
00097 }
00098 
00099 /*
00100  * ARC4 cipher function
00101  */
00102 int arc4_crypt( arc4_context *ctx, size_t length, const unsigned char *input,
00103                 unsigned char *output )
00104 {
00105     int x, y, a, b;
00106     size_t i;
00107     unsigned char *m;
00108 
00109     x = ctx->x ;
00110     y = ctx->y ;
00111     m = ctx->m ;
00112 
00113     for( i = 0; i < length; i++ )
00114     {
00115         x = ( x + 1 ) & 0xFF; a = m[x];
00116         y = ( y + a ) & 0xFF; b = m[y];
00117 
00118         m[x] = (unsigned char) b;
00119         m[y] = (unsigned char) a;
00120 
00121         output[i] = (unsigned char)
00122             ( input[i] ^ m[(unsigned char)( a + b )] );
00123     }
00124 
00125     ctx->x  = x;
00126     ctx->y  = y;
00127 
00128     return( 0 );
00129 }
00130 
00131 #endif /* !POLARSSL_ARC4_ALT */
00132 
00133 #if defined(POLARSSL_SELF_TEST)
00134 /*
00135  * ARC4 tests vectors as posted by Eric Rescorla in sep. 1994:
00136  *
00137  * http://groups.google.com/group/comp.security.misc/msg/10a300c9d21afca0
00138  */
00139 static const unsigned char arc4_test_key[3][8] =
00140 {
00141     { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF },
00142     { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF },
00143     { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }
00144 };
00145 
00146 static const unsigned char arc4_test_pt[3][8] =
00147 {
00148     { 0x01, 0x23, 0x45, 0x67, 0x89, 0xAB, 0xCD, 0xEF },
00149     { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 },
00150     { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }
00151 };
00152 
00153 static const unsigned char arc4_test_ct[3][8] =
00154 {
00155     { 0x75, 0xB7, 0x87, 0x80, 0x99, 0xE0, 0xC5, 0x96 },
00156     { 0x74, 0x94, 0xC2, 0xE7, 0x10, 0x4B, 0x08, 0x79 },
00157     { 0xDE, 0x18, 0x89, 0x41, 0xA3, 0x37, 0x5D, 0x3A }
00158 };
00159 
00160 /*
00161  * Checkup routine
00162  */
00163 int arc4_self_test( int verbose )
00164 {
00165     int i, ret = 0;
00166     unsigned char ibuf[8];
00167     unsigned char obuf[8];
00168     arc4_context ctx;
00169 
00170     arc4_init( &ctx );
00171 
00172     for( i = 0; i < 3; i++ )
00173     {
00174         if( verbose != 0 )
00175             polarssl_printf( "  ARC4 test #%d: ", i + 1 );
00176 
00177         memcpy( ibuf, arc4_test_pt[i], 8 );
00178 
00179         arc4_setup( &ctx, arc4_test_key[i], 8 );
00180         arc4_crypt( &ctx, 8, ibuf, obuf );
00181 
00182         if( memcmp( obuf, arc4_test_ct[i], 8 ) != 0 )
00183         {
00184             if( verbose != 0 )
00185                 polarssl_printf( "failed\n" );
00186 
00187             ret = 1;
00188             goto exit;
00189         }
00190 
00191         if( verbose != 0 )
00192             polarssl_printf( "passed\n" );
00193     }
00194 
00195     if( verbose != 0 )
00196         polarssl_printf( "\n" );
00197 
00198 exit:
00199     arc4_free( &ctx );
00200 
00201     return( ret );
00202 }
00203 
00204 #endif /* POLARSSL_SELF_TEST */
00205 
00206 #endif /* POLARSSL_ARC4_C */
00207