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September 28, 2014 00:36
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how to generate minecraft hex digests in java
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| package com.serverid; | |
| import java.io.UnsupportedEncodingException; | |
| import java.security.MessageDigest; | |
| import java.security.NoSuchAlgorithmException; | |
| public class ServerID | |
| { | |
| final protected static char[] hexArray = "0123456789ABCDEF".toCharArray(); | |
| public static void main(String[] args) | |
| { | |
| // The test values provided on http://wiki.vg/Protocol_Encryption are: | |
| // sha1(Notch) : 4ed1f46bbe04bc756bcb17c0c7ce3e4632f06a48 | |
| // sha1(jeb_) : -7c9d5b0044c130109a5d7b5fb5c317c02b4e28c1 | |
| System.out.println(javaHexDigest("Notch")); | |
| System.out.println(javaHexDigest("jeb_")); | |
| } | |
| private static String javaHexDigest(String data) | |
| { | |
| MessageDigest digest = null; | |
| try { | |
| digest = MessageDigest.getInstance("SHA-1"); | |
| digest.reset(); | |
| digest.update(data.getBytes("UTF-8")); | |
| } catch (NoSuchAlgorithmException e) { | |
| e.printStackTrace(); | |
| } catch (UnsupportedEncodingException e) { | |
| e.printStackTrace(); | |
| } | |
| byte[] hash = digest.digest(); | |
| boolean negative = (hash[0] & 0x80) == 0x80; | |
| if (negative) | |
| hash = twosCompliment(hash); | |
| String digests = getHexString(hash); | |
| if (digests.startsWith("0")) | |
| { | |
| digests = digests.replaceFirst("0", digests); | |
| } | |
| if (negative) | |
| { | |
| digests = "-" + digests; | |
| } | |
| digests = digests.toLowerCase(); | |
| return digests; | |
| } | |
| public static String getHexString(byte[] bytes) { | |
| char[] hexChars = new char[bytes.length * 2]; | |
| int v; | |
| for ( int j = 0; j < bytes.length; j++ ) { | |
| v = bytes[j] & 0xFF; | |
| hexChars[j * 2] = hexArray[v >>> 4]; | |
| hexChars[j * 2 + 1] = hexArray[v & 0x0F]; | |
| } | |
| return new String(hexChars); | |
| } | |
| private static byte[] twosCompliment(byte[] p) | |
| { | |
| int i; | |
| boolean carry = true; | |
| for (i = p.length - 1; i >= 0; i--) | |
| { | |
| p[i] = (byte)~p[i]; | |
| if (carry) | |
| { | |
| carry = p[i] == 0xFF; | |
| p[i]++; | |
| } | |
| } | |
| return p; | |
| } | |
| } |
This code is broken.
This code will not generate correct hashes in a lot of cases. I wrote a small test suite to generate 2000 random strings, and compare the hashed value to the one generated by vanilla (effectively new BigInteger(md.digest()).toString(16)). I found it has a 13% failure rate, and here are some examples of the way this fails:
Hashing L3CcLplRqgIvKtzb... FAIL
Vanilla: 8908b881f6827e31dfac8dd5da2748cba79a690
ServerID: 08908b881f6827e31dfac8dd5da2748cba79a6908908b881f6827e31dfac8dd5da2748cba79a690
Standard: 08908b881f6827e31dfac8dd5da2748cba79a690
Hashing pTJ3pyyOPblCiJ1y... FAIL
Vanilla: -f1b407986637d137df41cb29a921bfacb5e6031
ServerID: -0f1b407986637d137df41cb29a921bfacb5e6031f1b407986637d137df41cb29a921bfacb5e6031
Standard: f0e4bf86799c82ec820be34d656de40534a19fcf
Hashing BlFBO4ZN5igrMxoB... FAIL
Vanilla: -80c2b00389a1ee2ed0d3ea1808b0847d227271e
ServerID: -080c2b00389a1ee2ed0d3ea1808b0847d227271e80c2b00389a1ee2ed0d3ea1808b0847d227271e
Standard: f7f3d4ffc765e11d12f2c15e7f74f7b82dd8d8e2
Final output from the test suite: Done. 273/2000 failed (13% failure rate)
In short, DO NOT USE THIS CODE. It will silently fail in subtle ways, which will result in server authentication failing for seemingly no reason... 13% of the time.
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