Question

I am trying to input a text file that contains MD5 hashes and keywords (one per line) into a C# app. Is there a way to check if a string is an MD5 hash? I looked on MSDN and couldn t find anything in the MD5 class.

Answer 1

Use Regex like this:

public static bool IsMD5(string input)
{
    if (String.IsNullOrEmpty(input))
    {
        return false;
    }

    return Regex.IsMatch(input, "^[0-9a-fA-F]{32}$", RegexOptions.Compiled);
}

Answer 2

Well, an MD5 hash is really just binary data - if you ve got a string then it s presumably encoded in some fashion, e.g. base64 or hex. You can test whether the string is correctly encoded for the right length of binary (16 bytes). That s all though - while there may be binary values which are never the result of hashing any data, I highly doubt that you can recognise such values. Ideally, there should be no such values, of course...

Answer 3

A MD5 hash is a 128 bit value. It is usually represented as a byte[] with a length of 16, or as a string where each byte is represented by two hexadecimal digits. A MD5 hash has no internal structure or any kind of signature that allows you detect if a 128 bit value is a MD5 hash or not.

Answer 4

if its 32 bytes long and 0-9 a-f its probably md5, but not 100%

Answer 5

First thing to do is examine the file to work out how the MD5 hashes are encoded, then design a match based on that.

Answer 6

I think the correct one is this one that includes also the capitals sometimes hashes come also in capitals so why miss that.

[0-9a-fA-F]{32}

or

[0-9a-f]{32}(?i)

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