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[]"

You want to get the hash as hex not binary... I don't do c# though so I don't know how — Greg, Apr 17 '09 at 12:11
Just as a heads up, you might want to use SHAx since MD5 is being phased out. — Spencer Ruport, Apr 17 '09 at 12:32
The only reason to discontinue using MD5 is because of the cryptographic attacks against it recently (same with SHA-0/1). If you're not using it for cryptographic reasons, there's no big hurry to change over. — Jonathan Rupp, Apr 17 '09 at 12:45
For simple hashing without security considerations MD5 should still be enough. — Joey, Apr 17 '09 at 12:45

LukeH · Answer 1 · 2009-06-03T16:19:08.570

21

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);

edited Jun 03 '09 at 16:19

answered Apr 17 '09 at 12:39

LukeH

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Note this uses hexadecimal encoding. – meandmycode Apr 17 '09 at 13:04

Jonathan Rupp · Answer 2 · 2009-04-17T12:42:32.437

11

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("/","_");

edited Apr 17 '09 at 12:42

answered Apr 17 '09 at 12:11

Jonathan Rupp

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I am gettig an error using that and if try with say test.jpg it works?? – Malcolm Apr 17 '09 at 12:24
Looking at it there is "/" in the string and error is cannot find part pf path?? – Malcolm Apr 17 '09 at 12:27
Either remove all "/" characters or use the approach I suggest in my answer. – sharptooth Apr 17 '09 at 12:35
You will need to convert all the / and + characters to, say, _ and - characters instead. – C. K. Young Apr 17 '09 at 12:36
"+" characters are not prohibited, no need to remove them. – sharptooth Apr 17 '09 at 12:38
Converting to base 64 could have been a good idea, if it where not for the strange characters such as + - / that happens a lot when you use this encoding and that filesystems and parsers don't like – Johan Buret Apr 17 '09 at 12:46

score 3 · Answer 3 · edited Jun 21 '12 at 20:37

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

edited Jun 21 '12 at 20:37

Alexander

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answered Jun 21 '12 at 18:46

D.Gjinovci

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Note that Base64 produces case-sensitive names because it uses both capital and lower letters. Windows file systems are case-insensitive so be carefull with that. – nzeemin May 13 '15 at 11:02

score 3 · Answer 4 · answered Dec 02 '11 at 03:37

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();

score 3 · Answer 5 · answered Jun 03 '09 at 16:24

3

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)

answered Jun 03 '09 at 16:24

jrista

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Guid.ToString() uses NOT the sequential order of the originating byte array! – springy76 May 27 '14 at 10:12

score 1 · Answer 6 · answered Jul 26 '12 at 23:31

1

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]));
    }

answered Jul 26 '12 at 23:31

Yury Chaikou

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Please note that MD5 is not FIPS-compliant and will throw exception on machines with FIPS-enabled. Use SHA1 instead. – Yury Chaikou Aug 20 '12 at 19:45

score 1 · Answer 7 · answered Apr 17 '09 at 13:09

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).

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

7 Answers7

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