How to convert an MD5 hash to a string and use it as a file name

Question

I am taking the MD5 hash of an image file and I want to use the hash as a filename.

How do I convert the hash to a string that is valid filename?

EDIT: toString() just gives "System.Byte[]"

Answer 1

How about this:

string filename = BitConverter.ToString(yourMD5ByteArray);

If you prefer a shorter filename without hyphens then you can just use:

string filename =
    BitConverter.ToString(yourMD5ByteArray).Replace("-", string.Empty);

Answer 2

System.Convert.ToBase64String

As a commenter pointed out -- normal base 64 encoding can contain a '/' character, which obivously will be a problem with filenames. However, there are other characters that are usable, such as an underscore - just replace all the '/' with an underscore.

string filename = Convert.ToBase64String(md5HashBytes).Replace("/","_");

Answer 3

Try this:

string Hash = Convert.ToBase64String(MD5.Create().ComputeHash(Encoding.UTF8.GetBytes("sample")));
//input "sample" returns = Xo/5v1W6NQgZnSLphBKb5g==

or

string Hash = BitConverter.ToString(MD5.Create().ComputeHash(Encoding.UTF8.GetBytes("sample")));
//input "sample" returns = 5E-8F-F9-BF-55-BA-35-08-19-9D-22-E9-84-12-9B-E6

Answer 4

This is probably the safest for file names. You always get a hex string and never worry about / or +, etc.

        byte[] data = md5Hash.ComputeHash(Encoding.UTF8.GetBytes(inputString));
        StringBuilder sBuilder = new StringBuilder();
        for (int i = 0; i < data.Length; i++)
        {
            sBuilder.Append(data[i].ToString("x2"));
        }
        string hashed = sBuilder.ToString();

Answer 5

Try this:

Guid guid = new Guid(md5HashBytes);
string hashString = guid.ToString("N"); 
// format: xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

string hashString = guid.ToString("D"); 
// format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

string hashString = guid.ToString("B"); 
// format: {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx}

string hashString = guid.ToString("P"); 
// format: (xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx)

Answer 6

Try Base32 hash of MD5. It gives filename-safe case insensitive strings.

    string Base32Hash(string input)
    {
        byte[] buf = MD5.Create().ComputeHash(Encoding.UTF8.GetBytes(input));
        return String.Join("", buf.Select(b => "abcdefghijklmonpqrstuvwxyz234567"[b & 0x1F]));
    }

Answer 7

Technically using Base64 is bad if this is Windows, filenames are case insensitive (at least in explorers view).. but in base64, 'a' is different to 'A', this means that perhaps unlikely but you end up with even higher rate of collision..

A better alternative is hexadecimal like the bitconverter class, or if you can- use base32 encoding (which after removing the padding from both base64 and base32, and in the case of 128bit, will give you similar length filenames).