Question

当使用Python simple-crypt（源here）加密某些任意数据时，我正在研究项目，然后在java应用程序中使用相同的加密数据。

我想了解JSSE和Pycrypto之间的概念差异。

这是进行加密的python部分（source）：

counter = Counter.new(HALF_BLOCK, prefix=salt[:HALF_BLOCK//8])
cipher = AES.new(cipher_key, AES.MODE_CTR, counter=counter)

这是我尝试java重新实现相同的操作：

SecretKeySpec key = new SecretKeySpec(cipher_key, "AES");
IvParameterSpec ivSpec = new IvParameterSpec(salt, 0, HALF_BLOCK / 8);
Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);

这里的问题是java Cipher抛出异常的初始化：

java.security.InvalidAlgorithmParameterException: IV must be 16 bytes long.
    at org.bouncycastle.jce.provider.JCEBlockCipher.engineInit(Unknown Source)
    at javax.crypto.Cipher.init(Cipher.java:1394)
    at javax.crypto.Cipher.init(Cipher.java:1327)

HALF_BLOCK的值为64。

所以问题是，python的AES实现如何与HALF_BLOCK / 8密钥大小和java不兼容？

谢谢！

Answer 1

nonce（IV的“左侧”;“right”是顺序计数器）应作为IV与密文一起传输。没有必要保持nonce秘密。只有不得重新使用由同一密钥加密的其他邮件。

似乎Python代码正在生成一个Counter位长的新64，并将prefix（我假设nonce值）设置为8变量的前salt个字节。它很可能（这里因为我无法访问Python代码而有很大的假设）在0x00 * 8处启动实际的计数器值，因此您的初始IV将是：

salt = '#Eg����' # => UTF-8 encoding of 0x0123456789ABCDEF (not familiar enough with Python for the actual expression)
# Really may be misunderstanding, but as the AES IV must be 16 bytes, I imagine the terminology here is prefix = 8 bytes, sequence = 8 bytes
counter = Counter.new(HALF_BLOCK, prefix=salt[:HALF_BLOCK]) # => '0x01234567 89ABCDEF 00000000 00000000'
# Perform one encryption
counter # => '0x01234567 89ABCDEF 00000000 00000001'
# etc.

要在Java中执行相同的操作，它应该像将IvParameterSpec初始化为与上面相同一样简单（即将带有0的盐的前8个字节右键填充到16个字节）。

// Intentionally verbose for demonstration; this can obviously be compacted
byte[] salt = org.bouncycastle.util.encoders.Hex.decode("0123456789ABCDEF");
byte[] nonceAndCounter = new byte[16];
System.arraycopy(salt, 0, nonceAndCounter, 0, ((int) (HALF_BLOCK / 8)));
IvParameterSpec iv = new IvParameterSpec(nonceAndCounter);

这是一个完整的测试用例，断言加密和解密是内部兼容的;你也可以使用Python端的数据运行它来验证。

    @Test
    public void testPythonCompatibility() {
        // Arrange
        byte[] cipher_key = org.bouncycastle.util.encoders.Hex.decode("0123456789ABCDEFFEDCBA9876543210");
        final int HALF_BLOCK = 64;
        byte[] salt = org.bouncycastle.util.encoders.Hex.decode("0123456789ABCDEF");
        byte[] nonceAndCounter = new byte[16];
        System.arraycopy(salt, 0, nonceAndCounter, 0, ((int) (HALF_BLOCK / 8)));
        IvParameterSpec iv = new IvParameterSpec(nonceAndCounter);
        Cipher cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
        SecretKeySpec key = new SecretKeySpec(cipher_key, "AES");
        cipher.init(Cipher.ENCRYPT_MODE, key, iv);

        final String plaintext = "This is a plaintext message.";

        // Act
        byte[] cipherBytes = cipher.doFinal(plaintext.getBytes(StandardCharsets.UTF_8));

        // Assert
        cipher.init(Cipher.DECRYPT_MODE, key, iv);
        byte[] recoveredBytes = cipher.doFinal(cipherBytes);
        String recovered = new String(recoveredBytes, StandardCharsets.UTF_8);
        assert recovered.equals(plaintext);
    }

需要有关AES CTR cipher python与Java

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