src/org/bouncycastle/crypto/engines/RC4Engine.java

   1 package org.bouncycastle.crypto.engines;\r
   2 \r
   3 import org.bouncycastle.crypto.StreamCipher;\r
   4 import org.bouncycastle.crypto.CipherParameters;\r
   5 import org.bouncycastle.crypto.DataLengthException;\r
   6 import org.bouncycastle.crypto.params.KeyParameter;\r
   7 \r
   8 public class RC4Engine implements StreamCipher\r
   9 {\r
  10     private final static int STATE_LENGTH = 256;\r
  11 \r
  12     /*\r
  13      * variables to hold the state of the RC4 engine\r
  14      * during encryption and decryption\r
  15      */\r
  16 \r
  17     private byte[]      engineState = null;\r
  18     private int         x = 0;\r
  19     private int         y = 0;\r
  20     private byte[]      workingKey = null;\r
  21 \r
  22     /**\r
  23      * initialise a RC4 cipher.\r
  24      *\r
  25      * @param forEncryption whether or not we are for encryption.\r
  26      * @param params the parameters required to set up the cipher.\r
  27      * @exception IllegalArgumentException if the params argument is\r
  28      * inappropriate.\r
  29      */\r
  30     public void init(\r
  31         boolean             forEncryption, \r
  32         CipherParameters     params\r
  33     )\r
  34     {\r
  35         if (params instanceof KeyParameter)\r
  36         {\r
  37             /* \r
  38              * RC4 encryption and decryption is completely\r
  39              * symmetrical, so the 'forEncryption' is \r
  40              * irrelevant.\r
  41              */\r
  42             workingKey = ((KeyParameter)params).getKey();\r
  43             setKey(workingKey);\r
  44 \r
  45             return;\r
  46         }\r
  47 \r
  48         throw new IllegalArgumentException("invalid parameter passed to RC4 init - " + params.getClass().getName());\r
  49     }\r
  50 \r
  51     public String getAlgorithmName()\r
  52     {\r
  53         return "RC4";\r
  54     }\r
  55 \r
  56     public byte returnByte(byte in)\r
  57     {\r
  58         x = (x + 1) & 0xff;\r
  59         y = (engineState[x] + y) & 0xff;\r
  60 \r
  61         // swap\r
  62         byte tmp = engineState[x];\r
  63         engineState[x] = engineState[y];\r
  64         engineState[y] = tmp;\r
  65 \r
  66         // xor\r
  67         return (byte)(in ^ engineState[(engineState[x] + engineState[y]) & 0xff]);\r
  68     }\r
  69 \r
  70     public void processBytes(\r
  71         byte[]     in, \r
  72         int     inOff, \r
  73         int     len, \r
  74         byte[]     out, \r
  75         int     outOff\r
  76     )\r
  77     {\r
  78         if ((inOff + len) > in.length)\r
  79         {\r
  80             throw new DataLengthException("input buffer too short");\r
  81         }\r
  82 \r
  83         if ((outOff + len) > out.length)\r
  84         {\r
  85             throw new DataLengthException("output buffer too short");\r
  86         }\r
  87 \r
  88         for (int i = 0; i < len ; i++)\r
  89         {\r
  90             x = (x + 1) & 0xff;\r
  91             y = (engineState[x] + y) & 0xff;\r
  92 \r
  93             // swap\r
  94             byte tmp = engineState[x];\r
  95             engineState[x] = engineState[y];\r
  96             engineState[y] = tmp;\r
  97 \r
  98             // xor\r
  99             out[i+outOff] = (byte)(in[i + inOff]\r
 100                     ^ engineState[(engineState[x] + engineState[y]) & 0xff]);\r
 101         }\r
 102     }\r
 103 \r
 104     public void reset()\r
 105     {\r
 106         setKey(workingKey);\r
 107     }\r
 108 \r
 109     // Private implementation\r
 110 \r
 111     private void setKey(byte[] keyBytes)\r
 112     {\r
 113         workingKey = keyBytes;\r
 114 \r
 115         // System.out.println("the key length is ; "+ workingKey.length);\r
 116 \r
 117         x = 0;\r
 118         y = 0;\r
 119 \r
 120         if (engineState == null)\r
 121         {\r
 122             engineState = new byte[STATE_LENGTH];\r
 123         }\r
 124 \r
 125         // reset the state of the engine\r
 126         for (int i=0; i < STATE_LENGTH; i++)\r
 127         {\r
 128             engineState[i] = (byte)i;\r
 129         }\r
 130         \r
 131         int i1 = 0;\r
 132         int i2 = 0;\r
 133 \r
 134         for (int i=0; i < STATE_LENGTH; i++)\r
 135         {\r
 136             i2 = ((keyBytes[i1] & 0xff) + engineState[i] + i2) & 0xff;\r
 137             // do the byte-swap inline\r
 138             byte tmp = engineState[i];\r
 139             engineState[i] = engineState[i2];\r
 140             engineState[i2] = tmp;\r
 141             i1 = (i1+1) % keyBytes.length; \r
 142         }\r
 143     }\r
 144 }\r