XOR operation to Two Hex string

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Hi,

I have two hex strings and I need to do the XOR operation to that strings. I try with some methods but it not work well for me.

Eg:

C#

string PinBlock = "042241FFFFFFFFFF";
string CardBlock = "0000665702007894";

and the result shoud me afet XOR (Expected Result)
0422 27A8 FDFF 876B

This is what I tried so far

C#

public static string xorIt(string key, string input)
        {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < input.Length; i++)
                sb.Append((char)(input[i] ^ key[(i % key.Length)]));
            String result = sb.ToString();

            return result;
        }

        public string ASCIITOHex(string ascii)
        {

            StringBuilder sb = new StringBuilder();

            byte[] inputBytes = Encoding.UTF8.GetBytes(ascii);

            foreach (byte b in inputBytes)
            {

                sb.Append(string.Format("{0:x2}", b));

            }

            return sb.ToString();

        }

But from this I get below result

000402020207737176747676717e7f72

Posted 12-Mar-15 22:17pm

Soft009

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Comments

Tomas Takac 13-Mar-15 4:30am

The problem is you are XORing the char values. You need to convert them to numbers (ints) first then xor them then convert to chars (hex digit representation).

2 solutions

Solution 2

Quote:
sb.Append((char)(input[i] ^ key[(i % key.Length)]));

This line is wrong: you should not XOR the hexadecimal representation of the numbers, you have to XOR their actual values.

For instance,
0xF ^ 0x3 = 0xC (good)
while
'F' ^ '3' = 0x46 ^ 0x33 = 0x75 (not so good)

Posted 12-Mar-15 22:34pm

CPallini

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gdgajjar · Accepted Answer · 2015-03-12T22:28:00

Solution 1

C#

string hex1 = "042241FFFFFFFFFF";
          string hex2 = "0000665702007894";
          long dec1 = Convert.ToInt64(hex1, 16);
          long dec2 = Convert.ToInt64(hex2, 16);
          long result = dec1 ^ dec2;
          string hexResult = result.ToString("X");

Posted 12-Mar-15 22:28pm

gdgajjar

Comments

Soft009 13-Mar-15 4:31am

Thanks a lot