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1 /**
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2 * This file is part of the dcrypt project.
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3 *
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4 * Copyright: Copyright (C) dcrypt contributors 2008. All rights reserved.
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5 * License: MIT
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6 * Authors: Thomas Dixon
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7 */
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8
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9 module dcrypt.crypto.modes.CTR;
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10
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11 import dcrypt.crypto.BlockCipher;
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12 import dcrypt.crypto.params.ParametersWithIV;
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13
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14
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15 /** This class implements the counter (CTR/SIC/ICM) block mode,
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16 treating the counter as a big endian integer. */
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17 class CTR : BlockCipher {
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18 private BlockCipher m_cipher;
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19 private ubyte[] iv,
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20 counter,
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21 counterOutput;
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22 private bool initialized = false;
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23
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24 /**
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25 * Params:
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26 * cipher = Block cipher to wrap.
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27 */
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28 this (BlockCipher cipher) {
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29 m_cipher = cipher;
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30 }
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31
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32 /** Returns: The underlying cipher we are wrapping. */
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33 BlockCipher cipher() {
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34 return m_cipher;
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35 }
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36
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37 char[] name() {
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38 return m_cipher.name~"/CTR";
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39 }
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40
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41 /**
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42 * Throws: dcrypt.crypto.errors.InvalidParameterError if params aren't
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43 * an instance of dcrypt.crypto.params.ParametersWithIV.
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44 */
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45 void init(bool encrypt, CipherParameters params) {
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46 ParametersWithIV ivParams = cast(ParametersWithIV)params;
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47
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48 if (!ivParams)
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49 throw new InvalidParameterError(
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50 name()~": Block mode requires IV (use ParametersWithIV)");
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51 if (ivParams.iv.length != blockSize)
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52 throw new InvalidParameterError(
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53 name()~": IV must be same length as cipher block size");
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54
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55 m_cipher.init(true, ivParams.parameters);
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56
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57 iv = ivParams.iv[0..blockSize];
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58 counter = new ubyte[blockSize];
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59 counter[] = iv;
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60 counterOutput = new ubyte[blockSize];
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61
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62 initialized = true;
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63 }
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64
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65 uint processBlock(void[] input_, uint inOff, void[] output_, uint outOff) {
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66 if (!initialized)
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67 throw new NotInitializedError(
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68 name()~": Block mode not initialized");
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69
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70 ubyte[] input = cast(ubyte[]) input_;
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71 ubyte[] output = cast(ubyte[]) output_;
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72
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73 // Encrypt the counter
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74 m_cipher.processBlock(counter, 0, counterOutput, 0);
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75
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76 // XOR output with plaintext to create ciphertext
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77 for (int i = 0; i < counter.length; i++)
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78 output[outOff++] = (counterOutput[i] ^ input[inOff++]);
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79
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80 // Increment the counter
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81 for (int i = counter.length-1; i >= 0; i--)
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82 if (++counter[i]) break;
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83
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84 return counter.length;
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85 }
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86
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87 uint blockSize() {
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88 return m_cipher.blockSize;
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89 }
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90
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91 void reset() {
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92 counter[] = iv;
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93 m_cipher.reset();
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94 }
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95 }
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