java矩阵换位加密

这是一个简单的矩阵换位算法的java语言实现。

package sun.netsecurity.matrixtran;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
public class MatrixTransposition {
	
	private static BufferedReader br;
	
	static {
		InputStreamReader reader = new InputStreamReader(System.in);
		br = new BufferedReader(reader);
	}
	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {
		char[] plaintext = inputPlaintext();
		Integer key = inputKey();
		
		br.close();
		String ciphertext = encrypt(plaintext, key);
		System.out.println("明文加密后为: " + ciphertext);
		String plaintextStr = decrypt(ciphertext.toCharArray(), plaintext, key);
		System.out.println("密文解密后为: " + plaintextStr);
	}
	/**
	 * 将明文字符数组分组
	 * 
	 * @param plaintext
	 *            明文字符数组
	 * @param key
	 *            密钥
	 * @return
	 */
	static char[][] groupPlaintext(char[] plaintext, Integer key) {
		char[][] plaintextGroup = null;
		Integer length = plaintext.length;
		if (length % key != 0) {// 当字符数组的长度不是密钥的整数倍时，用字符'$'填补
			String plaintextStr = new String(plaintext);
			BigInteger lengthBI = new BigInteger(length.toString());
			BigInteger keyBI = new BigInteger(key.toString());
			BigInteger mod = lengthBI.mod(keyBI);
			int fillNumber = keyBI.intValue() - mod.intValue();
			for (int i = 0; i < fillNumber; i++) {
				plaintextStr = plaintextStr + "$";
			}
			plaintext = plaintextStr.toCharArray();
			length = plaintext.length;
		}
		int groupAmount = length / key;
		plaintextGroup = new char[groupAmount][key];
		for (int i = 0; i < groupAmount; i++) {
			for (int j = 0; j < key; j++) {
				// 将明文字符数组分割为二维数组
				plaintextGroup[i][j] = plaintext[i * key + j];
			}
		}
		return plaintextGroup;
	}
	/**
	 * 将密文分组
	 * 
	 * @param ciphertext
	 *            密文
	 * @param key
	 *            密钥
	 * @return
	 */
	static char[][] groupCiphertext(char[] ciphertext, Integer key) {
		char[][] ciphertextGroup = null;
		int length = ciphertext.length;
		int groupAmount = length / key;
		ciphertextGroup = new char[groupAmount][key];
		for (int i = 0; i < groupAmount; i++) {
			for (int j = 0; j < key; j++) {
				ciphertextGroup[i][j] = ciphertext[i * key + j];
			}
		}
		return ciphertextGroup;
	}
	/**
	 * 按照加密规则，将分割后的各个子字符数组分别进行移位
	 * 
	 * @param group
	 *            每一个子字符数组
	 * @return
	 */
	static char[] changePlaintext(char[] group) {
		char[] newGroup = new char[group.length];
		for (int i = 0; i < group.length; i++) {
			if (i == 0) {
				newGroup[0] = group[group.length - 1];
				continue;
			}
			newGroup[i] = group[i - 1];
		}
		return newGroup;
	}
	/**
	 * 
	 * @param group
	 *            按照加密规则,将密文分割后的各个子字符数组按照相反的方式分别进行移位
	 * @return
	 */
	static char[] changeCiphertext(char[] group) {
		char[] newGroup = new char[group.length];
		for (int i = 0; i < group.length; i++) {
			if (i == group.length - 1) {
				newGroup[group.length - 1] = group[0];
				break;
			}
			newGroup[i] = group[i + 1];
		}
		return newGroup;
	}
	static String getCipherFromGroup(char[][] plaintextGroup) {
		String ciphertext = "";
		int rowAccount = plaintextGroup.length;
		int lowAccount = plaintextGroup[0].length;
		for (int i = 0; i < rowAccount; i++) {
			char[] rowChar = new char[lowAccount];
			for (int j = 0; j < lowAccount; j++) {
				rowChar[j] = plaintextGroup[i][j];
			}
			ciphertext = ciphertext + new String(rowChar);
		}
		return ciphertext;
	}
	static String getPlaintextFromGroup(char[][] ciphertextGroup) {
		String plaintext = "";
		int rowAccount = ciphertextGroup.length;
		int lowAccount = ciphertextGroup[0].length;
		for (int i = 0; i < rowAccount; i++) {
			char[] rowChar = new char[lowAccount];
			for (int j = 0; j < lowAccount; j++) {
				rowChar[j] = ciphertextGroup[i][j];
			}
			plaintext = plaintext + new String(rowChar);
		}
		return plaintext;
	}
	// 从键盘输入明文
	static char[] inputPlaintext() {
		System.out.println("请输入明文:");
		char[] plaintextChar = null;
		try {
			String plaintext = null;
			plaintext = br.readLine();
			plaintextChar = plaintext.toCharArray();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return plaintextChar;
	}
	// 从键盘获得密钥
	static Integer inputKey() {
		System.out.println("请输入密钥:");
		Integer key = null;
		try {
			String keyString = null;
			keyString = br.readLine();
			key = new Integer(keyString);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return key;
	}
	/**
	 * 对明文进行加密
	 * 
	 * @param plaintext
	 *            明文
	 * @param key
	 *            密钥
	 * @return
	 */
	static String encrypt(char[] plaintext, Integer key) {
		String ciphertext;
		char[][] plaintextGroup;
		// 调用groupPlaintext(plaintext, key)方法对明文分组
		plaintextGroup = groupPlaintext(plaintext, key);
		for (int i = 0; i < plaintextGroup.length; i++) {
			// 调用changePlaintext(char[])进行位变换
			char[] rowText = changePlaintext(plaintextGroup[i]);
			plaintextGroup[i] = rowText;
		}
		//
		ciphertext = getCipherFromGroup(plaintextGroup);
		return ciphertext;
	}
	
	/**
	 * 对密文进行解密
	 * @param ciphertext 密文
	 * @param plaintext  明文
	 * @param key        密钥
	 * @return
	 */
	static String decrypt(char[] ciphertext, char[] plaintext, Integer key) {
		String plaintextStr;
		char[][] ciphertextGroup;
		ciphertextGroup = groupCiphertext(ciphertext, key);
		for (int i = 0; i < ciphertextGroup.length; i++) {
			char[] rowText = changeCiphertext(ciphertextGroup[i]);
			ciphertextGroup[i] = rowText;
		}
		
		plaintextStr = getPlaintextFromGroup(ciphertextGroup);
		Integer plaintextLength = plaintext.length;
		BigInteger pLenghBI = new BigInteger(plaintextLength.toString());
		BigInteger keyBI = new BigInteger(key.toString());
		BigInteger mod = pLenghBI.mod(keyBI);
		if (mod.intValue() != 0) {
			plaintextStr = plaintextStr.substring(0, plaintextStr.length()
					- (key - mod.intValue()));
		}
		return plaintextStr;
	}
}