Converting a 56-bit Value to a DES Key - Java Security

Java examples for Security:DES

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Description

Converting a 56-bit Value to a DES Key

Demo Code


import javax.crypto.SecretKey;
import javax.crypto.spec.DESKeySpec;
import javax.crypto.spec.SecretKeySpec;

public class Main {
  public static void m() {
    // Get the 56-bit value
    byte[] raw = new byte[] { 0x01, 0x72, 0x43, 0x3E, 0x1C, 0x7A, 0x55 };
    byte[] keyBytes = addParity(raw);

    // You can check that the parity has been set properly
    try {//  w w  w  .ja v a2s. com
      boolean b = DESKeySpec.isParityAdjusted(keyBytes, 0);
    } catch (java.security.InvalidKeyException e) {
      // The DES is invalid
    }

    // Convert the bytes into a SecretKey suitable for use by Cipher
    SecretKey key = new SecretKeySpec(keyBytes, "DES");
  }
  public static byte[] addParity(byte[] in) {
    byte[] result = new byte[8];
    // Keeps track of the bit position in the result
    int resultIx = 1;

    // Used to keep track of the number of 1 bits in each 7-bit chunk
    int bitCount = 0;

    // Process each of the 56 bits
    for (int i = 0; i < 56; i++) {
      // Get the bit at bit position i
      boolean bit = (in[6 - i / 8] & (1 << (i % 8))) > 0;

      // If set, set the corresponding bit in the result
      if (bit) {
        result[7 - resultIx / 8] |= (1 << (resultIx % 8)) & 0xFF;
        bitCount++;
      }

      // Set the parity bit after every 7 bits
      if ((i + 1) % 7 == 0) {
        if (bitCount % 2 == 0) {
          // Set low-order bit (parity bit) if bit count is even
          result[7 - resultIx / 8] |= 1;
        }
        resultIx++;
        bitCount = 0;
      }
      resultIx++;
    }
    return result;
  }
}

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