Android : How to create HMAC MD5 string? [closed]

Question

I am trying to create an android MD5 hash string to equal the C# code bellow:

private string CalculateHMACMd5(string message, string key)
{
     System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
     byte[] keyByte = encoding.GetBytes(key);
     HMACMD5 hmacmd5 = new HMACMD5(keyByte);
     byte[] messageBytes = encoding.GetBytes(message);
     byte[] hashmessage = hmacmd5.ComputeHash(messageBytes);
     string HMACMd5Value = ByteToString(hashmessage);
     return HMACMd5Value;
}

private static string ByteToString(byte[] buff)
{
    string sbinary = "";
    for (int i = 0; i < buff.Length; i++)
    {
        sbinary += buff[i].ToString("X2"); 
    }
    return (sbinary);
}

Android code that I currently use [not generating the same C# code]:

        public static String sStringToHMACMD5(String sData, String sKey) 
        {
            SecretKeySpec key;
            byte[] bytes;
            String sEncodedString = null;
            try 
            {       
                key = new SecretKeySpec((sKey).getBytes(), "ASCII");
                Mac mac = Mac.getInstance("HMACMD5");
                mac.init(key);
                mac.update(sData.getBytes());

                bytes = mac.doFinal(sData.getBytes());
                StringBuffer hash = new StringBuffer();

                for (int i=0; i<bytes.length; i++) {
                    String hex = Integer.toHexString(0xFF &  bytes[i]);
                    if (hex.length() == 1) {
                        hash.append('0');
                    }
                    hash.append(hex);
                }
            sEncodedString = hash.      
            return sEncodedString;
        }

Thanks in advance.

@Thilo: I checked the link you provided my self, the solution is not working. — Ahmad Kayyali
– Ahmad Kayyali, Commented Dec 6, 2011 at 7:21
+ the answer that you linked does not use 2 keys (data + key) — Ahmad Kayyali
– Ahmad Kayyali, Commented Dec 6, 2011 at 7:25

Basbous · Accepted Answer · 2011-12-06 07:31:05Z

21

public static String sStringToHMACMD5(String s, String keyString)
    {
        String sEncodedString = null;
        try
        {
            SecretKeySpec key = new SecretKeySpec((keyString).getBytes("UTF-8"), "HmacMD5");
            Mac mac = Mac.getInstance("HmacMD5");
            mac.init(key);

            byte[] bytes = mac.doFinal(s.getBytes("ASCII"));

            StringBuffer hash = new StringBuffer();

            for (int i=0; i<bytes.length; i++) {
                String hex = Integer.toHexString(0xFF &  bytes[i]);
                if (hex.length() == 1) {
                    hash.append('0');
                }
                hash.append(hex);
            }
            sEncodedString = hash.toString();
        }
        catch (UnsupportedEncodingException e) {}
        catch(InvalidKeyException e){}
        catch (NoSuchAlgorithmException e) {}
        return sEncodedString ;
    }

answered Dec 6, 2011 at 7:31

Basbous

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2 Comments

siamii Over a year ago

Don't ignore the exceptions. Log them.

Basbous Over a year ago

sure but i remove the Exception to reduce the code above.

Nikolay Elenkov · Accepted Answer · 2011-12-06 07:36:31Z

6

Define 'not working'. Exception? Output not as expected?, etc.

One obvious thing is that you are processing the same data twice:

mac.update(sData.getBytes());
bytes = mac.doFinal(sData.getBytes());

To process all data in one pass, just use doFinal() (assuming it's not too big). Another thing that can be wrong is the format of the key: what is the format of String sKey. Ideally you should be using a BASE64 encoded string, not calls to getString().

edited Dec 6, 2011 at 7:36

answered Dec 6, 2011 at 7:31

Nikolay Elenkov

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2 Comments

Basbous Over a year ago

I see your point you are correct, please check my solution, thanks for the hint.

Nikolay Elenkov Over a year ago

Dump (or use the debugger) in both programs the byte[] keyByte, make sure the bytes are the same. Do the same with byte[] messageBytes. If all those match, byte[] hashmessage should too, but check that as well. If those match, the error is in the final hex encoding part.

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