c# - 将 C++ 方法转换为 C#

Question

我有一个解密 base64 的方法，我需要将它转换为 C#，我尝试使用 C# 的 Convert.FromBase64String 和我在此处查看的其他一些提示，但最终字符串不匹配c++ 上的结果。

有人可以帮助理解这种和平的 C++ 代码吗？

示例输入:lWXtYpNpwBBXoLmcuktDqg==

预期输出:AC0105E92ED496ACD373D7496B76C1C8

使用 Convert.FromBase64 的输出:95-65-ED-62-93-69-C0-10-57-A0-B9-9C-BA-4B-43-AA

static BYTE BackFrom64[]={
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0x3e,0xff,0xff,0xff,0x3f,
0x34,0x35,0x36,0x37,0x38,0x39,0x3a,0x3b,
0x3c,0x3d,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0x00,0x01,0x02,0x03,0x04,0x05,0x06,
0x07,0x08,0x09,0x0a,0x0b,0x0c,0x0d,0x0e,
0x0f,0x10,0x11,0x12,0x13,0x14,0x15,0x16,
0x17,0x18,0x19,0xff,0xff,0xff,0xff,0xff,
0xff,0x1a,0x1b,0x1c,0x1d,0x1e,0x1f,0x20,
0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28,
0x29,0x2a,0x2b,0x2c,0x2d,0x2e,0x2f,0x30,
0x31,0x32,0x33,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff,
0xff,0xff,0xff,0xff,0xff,0xff,0xff,0xff

};

static BYTE * TabBase64=(BYTE *)"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";


int FromBase64(BYTE *Output,BYTE *Input,int BufSize,int MaxSize) {

    int              xut,txut;
    int              i,t,k,shift;
    BYTE             c;
    dWORD            dr,dr1;

    xut=txut=t=0;
    dr=0L;
    for(i=0; i < BufSize; ++i) {
        c=*Input++;
        if(c == '=') {
            break;
        }
        if((c=BackFrom64[c]) == 0xff) {
            continue;
        }
        dr1=(dWORD)c;
        shift=(32-(6*(t+1)));
        dr1<<=shift;
        dr|=dr1;
        t++;
        if(t == 4) {
            t=0;
            for(k=0; k < 3; ++k) {
                dr1=dr;
                dr1>>=(32-(8*(k+1)));
                dr1&=0xff;
                *Output++=(BYTE) dr1;
                if(++txut >= MaxSize) {
                    return(-1);
                }
            }
            dr=0;
        }
    }
    if(t > 0) {
        for(k=0; k < (t-1); ++k) {
            dr1=dr;
            dr1>>=(32-(8*(k+1)));
            dr1&=0xff;
            *Output++=(BYTE) dr1;
            if(++txut >= MaxSize) {
                return(-1);
            }
        }
    }
    return(txut);
}

Answer 1

接下来是一个非常简单的转换，只需最少的工作。

• 类型已更改为 C# 类型
• 指针增量已更改为数组索引

唯一的其他变化是将未提供的 BackFrom64 数组计算为 TabBase64 数组的倒数，并为提供的输入和输出添加单元测试。如果它做了标准算法以外的事情，那么我会整理计数器，其中一些是多余的(可能 i 和 iInput 都可以替换为 foreach(var c in input)

using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace SO
{
    [TestClass]
    public class UnitTest1
    {
        private const string TabBase64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
        private static readonly byte[] BackFrom64 = CreateBackFrom64();

        private static byte[] CreateBackFrom64()
        {
            var backFrom64 = new byte[128];

            for (var i = 0; i < backFrom64.Length; ++i)
                backFrom64[i] = 0xff;

            for (byte i = 0; i < TabBase64.Length; i++)
            {
                var c = TabBase64[i];
                backFrom64[c] = i;
            }

            return backFrom64;
        }

        int FromBase64(byte[] Output, string Input, int BufSize, int MaxSize)
        {
            int xut, txut;
            int i, t, k, shift;
            byte c;
            int dr, dr1;

            xut = txut = t = 0;
            dr = 0;

            var iInput = 0;
            var iOutput = 0;

            for (i = 0; i < BufSize; ++i)
            {
                c = (byte)Input[iInput++];
                if (c == '=')
                {
                    break;
                }
                if ((c = BackFrom64[c]) == 0xff)
                {
                    continue;
                }
                dr1 = c;
                shift = (32 - (6 * (t + 1)));
                dr1 <<= shift;
                dr |= dr1;
                t++;
                if (t == 4)
                {
                    t = 0;
                    for (k = 0; k < 3; ++k)
                    {
                        dr1 = dr;
                        dr1 >>= (32 - (8 * (k + 1)));
                        dr1 &= 0xff;
                        Output[iOutput++] = (byte)dr1;
                        if (++txut >= MaxSize)
                        {
                            return (-1);
                        }
                    }
                    dr = 0;
                }
            }
            if (t > 0)
            {
                for (k = 0; k < (t - 1); ++k)
                {
                    dr1 = dr;
                    dr1 >>= (32 - (8 * (k + 1)));
                    dr1 &= 0xff;
                    Output[iOutput++] = (byte)dr1;
                    if (++txut >= MaxSize)
                    {
                        return (-1);
                    }
                }
            }
            return (txut);
        }
        [TestMethod]
        public void TestMethod1()
        {
            var input = @"lWXtYpNpwBBXoLmcuktDqg==";
            var expectedOutput = "AC0105E92ED496ACD373D7496B76C1C8";

            var converted = new byte[(input.Length * 2) / 3];

            var result = FromBase64(converted, input, input.Length, int.MaxValue);

            Assert.AreNotEqual(-1, result, "result is valid");

            Assert.AreEqual(
                BitConverter.ToString(converted).Replace("-",""),
                BitConverter.ToString(Convert.FromBase64String(input)).Replace("-",""),
                "Supplied algorithm matches standard algorithm" );

            Assert.AreEqual(
                expectedOutput,
                BitConverter.ToString(converted).Replace("-",""),
                "Supplied algorithm matches expected output" );
        }
    }
}

现在，第一个断言通过，因为移植的代码返回与 Convert.FromBase64String 完全相同的结果，但第二个断言失败，因为这不是您所说的从 C++ 获得的输出。

据此我得出结论，最有可能造成差异的原因是调用 C++ 版本时，BackFrom64 的内容未正确初始化并且包含垃圾值 - 在对 OP 的编辑中提供的 BackFrom64 的值导致与计算结果相同的输出，因此预期结果会发生其他事情。编译 C++ 版本并使用给定的输入运行:

int main()
{
    const char* input = "lWXtYpNpwBBXoLmcuktDqg==";

    BYTE Input[100];
    BYTE Output[100];

    int length = strlen(input);

    memcpy(Input, input, length);

    int result = FromBase64(Output, Input, 100, length);

    for (int i = 0; i < result; ++i)
        std::cout << std::hex << (int)Output[i] << " ";

    std::cout << "\n";
}

生成输出

95 65 ed 62 93 69 c0 10 57 a0 b9 9c ba 4b 43 aa

这再次表明它与标准算法相同。