CODEWITHSUNDEEP
c#cryptographymifarecrc32desfire
Felix Arnold
Felix Arnold

Reputation: 901

C# Crc32 implementation

I´ve got the following example:

3D020000000F0000112233445566778899AABBCCDDEEFF - Crc32 Input
280ACDA5 - Crc32 Result

But with the following Calculators: sunshine2k and zorc.breitbandkatze I can´t reconstruct the result. The documentation says: Polynomial-04C11DB7, Reverse-EDB88320, Initvalue-FFFFFFFF and also the Result should not be reversed.

I´ve searched for libraries on NuGet and found Nito but do not get the right result either. I´ve also tried every combination with flags and polynomials (04C11DB7, EDB88320).

Can someone tell what I´m doing wrong? Are the calculators and the lib wrong? Also I´ve tried same combination of polinom and flags on both sides and the lib but got different result :-( may someone tell a lib which is definatly reight?

Here my Testcode:

        [Theory]
        [InlineData("3D 00 00 00 00 10 00 00 23 00 00 00 00 00 00 08 12 34 56 78 00 00 00 00", "7B 8A 60 0F")]
        [InlineData("3D020000000F0000112233445566778899AABBCCDDEEFF", "280ACDA5")]
        public void Crc32_Test(string input, string assumedCrc32)
        {
            var definition = new Definition
            {
                Initializer = 0xFFFFFFFF,
                TruncatedPolynomial = 0xEDB88320,
                ReverseResultBeforeFinalXor = false,
                ReverseDataBytes = false,
            };

            var whow = new Nito.HashAlgorithms.CRC32(definition);

            var inputArray = DESFireSessionHandler.StringToByte(input);
            var assumedCrc32Array = DESFireSessionHandler.StringToByte(assumedCrc32);

            var crc32 = whow.ComputeHash(inputArray);

            if (crc32.SequenceEqual(assumedCrc32Array))
                Assert.True(true);
            else if (crc32.Reverse().SequenceEqual(assumedCrc32Array))
                Assert.True(true);
            else Assert.False(true);
}

Upvotes: 3

Views: 3926

Answers (1)

Topaco
Topaco

Reputation: 49400

The following parameters produce the desired result 280ACDA5:

Initializer = 0xFFFFFFFF,
TruncatedPolynomial = 0x04C11DB7,
FinalXorValue = 0x00000000,
ReverseResultBeforeFinalXor = true,
ReverseDataBytes = true

This is identical (except for the order of the bytes) to the online tools:

https://crccalc.com/

enter image description here

http://www.sunshine2k.de/coding/javascript/crc/crc_js.html

enter image description here

The complete C# code is:

using System;
using static Nito.HashAlgorithms.CRC32;
                    
public class Program
{
    public static void Main()
    {
        var definition = new Definition
        {
            Initializer = 0xFFFFFFFF,
            TruncatedPolynomial = 0x04C11DB7,
            FinalXorValue = 0x00000000,
            ReverseResultBeforeFinalXor = true,
            ReverseDataBytes = true
        };

        var inputHex = "3D020000000F0000112233445566778899AABBCCDDEEFF";
        var input = Convert.FromHexString(inputHex);
        var whow = new Nito.HashAlgorithms.CRC32(definition);
        
        var crc32 = whow.ComputeHash(input);
        var crc32Hex = Convert.ToHexString(crc32);
        Console.WriteLine(crc32Hex); // 280ACDA5
    }
}

Upvotes: 5

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