md5 checksum on file in android doesn't match the md5 after i email it to myself

Question

The functions I'm using to convert the file to a string and then to an mdf are below. I'm outputting the file paths and file names to make sure everything is cool. Is there anything I'm not considering that could change the file's (a video mp4 actually) fingerprint? I'm checking it against md5sum on ubuntu.

private static String readFileToString(String filePath)
        throws java.io.IOException{

            StringBuffer fileData = new StringBuffer(1000);
            BufferedReader reader = new BufferedReader(
                    new FileReader(filePath));
            char[] buf = new char[1024];

            int numRead=0;
            while((numRead=reader.read(buf)) != -1){
                String readData = String.valueOf(buf, 0, numRead);
                fileData.append(readData);
                buf = new char[1024];
            }

            reader.close();
            System.out.println(fileData.toString());
            return fileData.toString();
        }

public static String getMD5EncryptedString(String encTarget){
  MessageDigest mdEnc = null;
  try {
      mdEnc = MessageDigest.getInstance("MD5");
  } catch (NoSuchAlgorithmException e) {
      System.out.println("Exception while encrypting to md5");
      e.printStackTrace();
  } // Encryption algorithm
  mdEnc.update(encTarget.getBytes(), 0, encTarget.length());
  String md5 = new BigInteger(1, mdEnc.digest()).toString(16) ;
  return md5;
}

user207421 · Answer 1 · 2013-07-20T02:34:18.243

5

String isn't a container for binary data. Lose the two conversions between byte array and String. You should be reading the file as bytes and computing the MD5 directly in the bytes. You can do that while you're reading it: you don't need to read the entire file first.

And MD5 isn't an encryption: it's a secure hash.

edited Jul 20 '13 at 02:34

answered Jul 20 '13 at 02:02

user207421

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Thanks for the tip. You were right, and I found some code in another question. That function name I copied! – Damien Justin Šutevski Jul 20 '13 at 05:28

score 3 · Accepted Answer · edited May 23 '17 at 12:14

Found this answer here: How to generate an MD5 checksum for a file in Android?

public static String fileToMD5(String filePath) {
InputStream inputStream = null;
try {
    inputStream = new FileInputStream(filePath);
    byte[] buffer = new byte[1024];
    MessageDigest digest = MessageDigest.getInstance("MD5");
    int numRead = 0;
    while (numRead != -1) {
        numRead = inputStream.read(buffer);
        if (numRead > 0)
            digest.update(buffer, 0, numRead);
    }
    byte [] md5Bytes = digest.digest();
    return convertHashToString(md5Bytes);
} catch (Exception e) {
    return null;
} finally {
    if (inputStream != null) {
        try {
            inputStream.close();
        } catch (Exception e) { }
    }
}
}

private static String convertHashToString(byte[] md5Bytes) {
String returnVal = "";
for (int i = 0; i < md5Bytes.length; i++) {
    returnVal += Integer.toString(( md5Bytes[i] & 0xff ) + 0x100, 16).substring(1);
}
return returnVal;
}

md5 checksum on file in android doesn't match the md5 after i email it to myself

2 Answers2