java - 如何在java中实现twofish加密来加密/解密字符串？

Question

我最近从https://www.schneier.com/academic/twofish/download.html下载了 twofish-java.zip 。里面有一个jar文件twofish.jar。有人向我解释了如何在 java 中实现 twofish 加密，以使用这个 jar 文件在 java 中加密/解密字符串

Answer 1

您需要实现这些功能blockEncrypt()并blockDecrypt()围绕它们构建一种操作模式。使用该函数创建密钥，该makeKey()函数需要 8、16、24 或 32 字节的密钥长度。确保将明文填充为 16 字节的倍数。我已将我的 ECB 和 CBC 模式代码附加到 Twofish 中。如果您想要最好的安全性，我建议您实现自己的填充功能和密钥扩展功能。在我的示例中，每个块使用相同的密钥，明文仅在末尾填充 0。

static byte[] ecbEncrypt(byte[] plaintext, byte[] key) throws InvalidKeyException {
    byte[] pt = pad(plaintext, 16);
    byte[] ciphertext = new byte[pt.length];
    for (int i = 0; i < pt.length; i += 16) {
        byte[] t = Twofish_Algorithm.blockEncrypt(pt, i, Twofish_Algorithm.makeKey(key));
        for (int j = i; j < i + 16; j++) 
            ciphertext[j] = t[j % 16];
    }
    return ciphertext;
}

static byte[] ecbDecrypt(byte[] ciphertext, byte[] key) throws InvalidKeyException {
    byte[] plaintext = new byte[ciphertext.length];
    for (int i = 0; i < ciphertext.length; i += 16) {
        byte[] t = Twofish_Algorithm.blockDecrypt(ciphertext, i, Twofish_Algorithm.makeKey(key));
        for (int j = i; j < i + 16; j++) 
            plaintext[j] = t[j % 16];
    }
    return unpad(plaintext);
}

static byte[] cbcEncrypt(byte[] plaintext, byte[] key, byte[] iv) throws InvalidKeyException {
    byte[] pt = pad(plaintext, 16);
    byte[] ciphertext = new byte[pt.length];
    for (int i = 0; i < 16; i++)
        pt[i] ^= iv[i];
    byte[] t = Twofish_Algorithm.blockEncrypt(pt, 0, Twofish_Algorithm.makeKey(key));
    for (int i = 0; i < 16; i++)
        ciphertext[i] = t[i];
    for (int i = 16; i < pt.length; i += 16) {
        for (int j = 0; j < 16; j++)
            pt[i + j] ^= ciphertext[i - 16 + j];
        byte[] t2 = Twofish_Algorithm.blockEncrypt(pt, i, Twofish_Algorithm.makeKey(key));
        for (int j = 0; j < 16; j++)
            ciphertext[i + j] = t2[j];
    }
    return ciphertext;
}

static byte[] cbcDecrypt(byte[] ciphertext, byte[] key, byte[] iv) throws InvalidKeyException {
    byte[] plaintext = new byte[ciphertext.length];
    byte[] t = Twofish_Algorithm.blockDecrypt(ciphertext, 0, Twofish_Algorithm.makeKey(key));
    for (int i = 0; i < 16; i++) 
        plaintext[i] = (byte) (t[i] ^ iv[i]);
    for (int i = 16; i < ciphertext.length; i += 16) {
        byte[] t2 = Twofish_Algorithm.blockDecrypt(ciphertext, i, Twofish_Algorithm.makeKey(key));
        for (int j = 0; j < 16; j++)
            plaintext[i + j] = (byte) (t2[j] ^ ciphertext[i - 16 + j]);
    }
    return unpad(plaintext);
}

static byte[] pad(byte[] in, int blockSize) {
    byte[] ret = new byte[in.length + blockSize - in.length % blockSize];
    for (int i = 0; i < in.length; i++) 
        ret[i] = in[i];
    byte paddedBytes = 0;
    for (int i = in.length; i < ret.length - 1; i++) {
        ret[i] = 0;
        paddedBytes++;
    }
    ret[ret.length - 1] = paddedBytes;
    return ret;
}

static byte[] unpad(byte[] in) {
    byte[] ret = new byte[in.length - in[in.length - 1] - 1];
    for (int i = 0; i < ret.length; i++) 
        ret[i] = in[i];
    return ret;
}

这个实现可能不会是完美的，所以请随时给我写改进，以便我可以编辑我的回复。

您可以像这样调用函数：

SecureRandom sr = new SecureRandom();

byte[] plaintext = "This is secret plaintext".getBytes();
byte[] key = new byte[16];
byte[] iv = new byte[16];
sr.nextBytes(key);
sr.nextBytes(iv);

System.out.println("Plaintext: " + new String(plaintext));
byte[] ecbCiphertext = ecbEncrypt(plaintext, key);
System.out.println("ECB-Ciphertext: " + new String(ecbCiphertext));
byte[] ecbPlaintext = ecbDecrypt(ecbCiphertext, key);
System.out.println("ECB-Plaintext: " + new String(ecbPlaintext));
byte[] cbcCiphertext = cbcEncrypt(plaintext, key, iv);
System.out.println("CBC-Ciphertext: " + new String(cbcCiphertext));
byte[] cbcPlaintext = cbcDecrypt(cbcCiphertext, key, iv);
System.out.println("CBC-Plaintext: " + new String(cbcPlaintext));

Plaintext: This is secret plaintext
ECB-Ciphertext: ÑìÔõ¬ŽÁ@γ÷ÊÑ–1—N,/ )ë+$
ECB-Plaintext: This is secret plaintext
CBC-Ciphertext: JÉÌÙ•=Hæí_•¤iÔ[%˜Å?ÆÍæ“!Ø?%
CBC-Plaintext: This is secret plaintext

如果您想要一种使用计数器模式加密/解密的方法，我也为此附加了我的实现。

static byte[] ctrEncrypt(byte[] plaintext, byte[] key, byte[] iv) throws InvalidKeyException {
    byte[] initializationVector = Arrays.copyOf(iv, iv.length);
    byte[] counter = { -128, -128, -128, -128, -128, -128, -128, -128 };
    byte[] ciphertext = new byte[plaintext.length];
    for (int i = 0; i < plaintext.length / 16 + 1; i++) {
        for (int j = 0; j < 8; j++) {
            if (counter[j] == 127 && j != 7) {                  counter[j] = -128;
                counter[j + 1]++;
            }
            if (counter[j] != -128)
                initializationVector[15 - j] = counter[j];
            else
                initializationVector[15-j] = iv[15-j];
        }
        byte[] t = Twofish_Algorithm.blockEncrypt(initializationVector, 0, Twofish_Algorithm.makeKey(key));
        for (int j = 0; i < plaintext.length / 16 ? j < 16 : j < plaintext.length % 16; j++)
            ciphertext[i * 16 + j] = (byte) (plaintext[i * 16 + j] ^ t[j]);
        counter[0]++;
    }
    return ciphertext;
}

static byte[] ctrDecrypt(byte[] ciphertext, byte[] key, byte[] iv) throws InvalidKeyException {
    return ctrEncrypt(ciphertext, key, iv);
}