Java 到 C#：从文档哈希计算代码

Question

我有 Java 代码示例，说明应如何计算验证码。而且我必须将 Java 代码转换为 C#。

首先，代码计算如下：

integer(SHA256(hash)[-2: -1]) mod 10000

在我们取SHA256结果的地方，从中提取最右边的2个字节，将它们解释为big-endian无符号整数，并取最后4位十进制数显示。

Java代码：

public static String calculate(byte[] documentHash) {
    byte[] digest = DigestCalculator.calculateDigest(documentHash, HashType.SHA256);
    ByteBuffer byteBuffer = ByteBuffer.wrap(digest);
    int shortBytes = Short.SIZE / Byte.SIZE; // Short.BYTES in java 8
    int rightMostBytesIndex = byteBuffer.limit() - shortBytes;
    short twoRightmostBytes = byteBuffer.getShort(rightMostBytesIndex);
    int positiveInteger = ((int) twoRightmostBytes) & 0xffff;
    String code = String.valueOf(positiveInteger);
    String paddedCode = "0000" + code;
    return paddedCode.substring(code.length());
  }

public static byte[] calculateDigest(byte[] dataToDigest, HashType hashType) {
    String algorithmName = hashType.getAlgorithmName();
    return DigestUtils.getDigest(algorithmName).digest(dataToDigest);
  }

所以来自 Base64 字符串的 int C#： 2afAxT+nH5qNYrfM+D7F6cKAaCKLLA23pj8ro3SksqwsdwmC3xTndKJotewzu7HlDy/DiqgkR+HXBiA0sW1x0Q==

计算代码应等于：3676

有什么实现方法吗？

Answer 1

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(GetCode("2afAxT+nH5qNYrfM+D7F6cKAaCKLLA23pj8ro3SksqwsdwmC3xTndKJotewzu7HlDy/DiqgkR+HXBiA0sW1x0Q=="));
    }


    public static string GetCode(string str)
    {
        var sha = System.Security.Cryptography.SHA256.Create();
        var hash = sha.ComputeHash(Convert.FromBase64String(str));
        var last2 = hash[^2..];
        var intVal = ((int) last2[0]) * 0x0100 + ((int) last2[1]);
        var digits = intVal % 10000;
        return $"{digits:0000}";            
    }
}

Java 到 C#：从文档哈希计算代码

Java to C#: code computing from document hash

c#

algorithm

sha256