131 lines
4.5 KiB
C#
131 lines
4.5 KiB
C#
using System;
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namespace Org.BouncyCastle.Crypto.Parameters
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{
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public class DesParameters
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: KeyParameter
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{
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public DesParameters(
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byte[] key)
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: base(key)
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{
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if (IsWeakKey(key))
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throw new ArgumentException("attempt to create weak DES key");
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}
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public DesParameters(
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byte[] key,
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int keyOff,
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int keyLen)
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: base(key, keyOff, keyLen)
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{
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if (IsWeakKey(key, keyOff))
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throw new ArgumentException("attempt to create weak DES key");
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}
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/*
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* DES Key Length in bytes.
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*/
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public const int DesKeyLength = 8;
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/*
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* Table of weak and semi-weak keys taken from Schneier pp281
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*/
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private const int N_DES_WEAK_KEYS = 16;
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private static readonly byte[] DES_weak_keys =
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{
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/* weak keys */
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(byte)0x01,(byte)0x01,(byte)0x01,(byte)0x01, (byte)0x01,(byte)0x01,(byte)0x01,(byte)0x01,
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(byte)0x1f,(byte)0x1f,(byte)0x1f,(byte)0x1f, (byte)0x0e,(byte)0x0e,(byte)0x0e,(byte)0x0e,
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(byte)0xe0,(byte)0xe0,(byte)0xe0,(byte)0xe0, (byte)0xf1,(byte)0xf1,(byte)0xf1,(byte)0xf1,
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(byte)0xfe,(byte)0xfe,(byte)0xfe,(byte)0xfe, (byte)0xfe,(byte)0xfe,(byte)0xfe,(byte)0xfe,
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/* semi-weak keys */
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(byte)0x01,(byte)0xfe,(byte)0x01,(byte)0xfe, (byte)0x01,(byte)0xfe,(byte)0x01,(byte)0xfe,
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(byte)0x1f,(byte)0xe0,(byte)0x1f,(byte)0xe0, (byte)0x0e,(byte)0xf1,(byte)0x0e,(byte)0xf1,
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(byte)0x01,(byte)0xe0,(byte)0x01,(byte)0xe0, (byte)0x01,(byte)0xf1,(byte)0x01,(byte)0xf1,
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(byte)0x1f,(byte)0xfe,(byte)0x1f,(byte)0xfe, (byte)0x0e,(byte)0xfe,(byte)0x0e,(byte)0xfe,
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(byte)0x01,(byte)0x1f,(byte)0x01,(byte)0x1f, (byte)0x01,(byte)0x0e,(byte)0x01,(byte)0x0e,
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(byte)0xe0,(byte)0xfe,(byte)0xe0,(byte)0xfe, (byte)0xf1,(byte)0xfe,(byte)0xf1,(byte)0xfe,
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(byte)0xfe,(byte)0x01,(byte)0xfe,(byte)0x01, (byte)0xfe,(byte)0x01,(byte)0xfe,(byte)0x01,
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(byte)0xe0,(byte)0x1f,(byte)0xe0,(byte)0x1f, (byte)0xf1,(byte)0x0e,(byte)0xf1,(byte)0x0e,
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(byte)0xe0,(byte)0x01,(byte)0xe0,(byte)0x01, (byte)0xf1,(byte)0x01,(byte)0xf1,(byte)0x01,
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(byte)0xfe,(byte)0x1f,(byte)0xfe,(byte)0x1f, (byte)0xfe,(byte)0x0e,(byte)0xfe,(byte)0x0e,
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(byte)0x1f,(byte)0x01,(byte)0x1f,(byte)0x01, (byte)0x0e,(byte)0x01,(byte)0x0e,(byte)0x01,
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(byte)0xfe,(byte)0xe0,(byte)0xfe,(byte)0xe0, (byte)0xfe,(byte)0xf1,(byte)0xfe,(byte)0xf1
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};
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/**
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* DES has 16 weak keys. This method will check
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* if the given DES key material is weak or semi-weak.
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* Key material that is too short is regarded as weak.
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* <p>
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* See <a href="http://www.counterpane.com/applied.html">"Applied
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* Cryptography"</a> by Bruce Schneier for more information.
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* </p>
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* @return true if the given DES key material is weak or semi-weak,
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* false otherwise.
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*/
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public static bool IsWeakKey(
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byte[] key,
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int offset)
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{
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if (key.Length - offset < DesKeyLength)
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throw new ArgumentException("key material too short.");
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//nextkey:
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for (int i = 0; i < N_DES_WEAK_KEYS; i++)
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{
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bool unmatch = false;
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for (int j = 0; j < DesKeyLength; j++)
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{
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if (key[j + offset] != DES_weak_keys[i * DesKeyLength + j])
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{
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//continue nextkey;
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unmatch = true;
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break;
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}
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}
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if (!unmatch)
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{
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return true;
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}
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}
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return false;
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}
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public static bool IsWeakKey(
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byte[] key)
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{
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return IsWeakKey(key, 0);
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}
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/**
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* DES Keys use the LSB as the odd parity bit. This can
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* be used to check for corrupt keys.
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*
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* @param bytes the byte array to set the parity on.
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*/
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public static void SetOddParity(
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byte[] bytes)
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{
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for (int i = 0; i < bytes.Length; i++)
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{
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int b = bytes[i];
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bytes[i] = (byte)((b & 0xfe) |
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((((b >> 1) ^
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(b >> 2) ^
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(b >> 3) ^
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(b >> 4) ^
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(b >> 5) ^
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(b >> 6) ^
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(b >> 7)) ^ 0x01) & 0x01));
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}
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}
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}
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}
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