Java Encode SHA-1 Byte Array

Question

I have an SHA-1 byte array that I would like to use in a GET request. I need to encode this. URLEncoder expects a string, and if I create a string of it and then encode it, it gets corrupt?

To clarify, this is kinda a follow up to another question of mine. (Bitorrent Tracker Request) I can get the value as a hex string, but that is not recognized by the tracker. On the other hand, encoded answer mark provided return 200 OK.

So I need to convert the hex representation that I got:

9a81333c1b16e4a83c10f3052c1590aadf5e2e20

into encoded form

%9A%813%3C%1B%16%E4%A8%3C%10%F3%05%2C%15%90%AA%DF%5E.%20

Answer 1

This depends on what the recipient of your request expects. I would imagine it could be a hexadecimal representation of the bytes in your hash. A string would probably not be the best idea, because the hash array will most likely contain non-printable character values.

I'd iterate over the array and use Integer.toHexValue() to convert the bytes to hex.

Answer 2

SHA1 is in hex format [0-9a-f], there should be no need to URLEncode it.

Answer 3

Question was edited while I was responding, following is ADDITIONAL code and should work (with my hex conversion code):

//Inefficient, but functional, does not test if input is in hex charset, so somewhat unsafe
//NOT tested, but should be functional
public static String encodeURL(String hexString) throws Exception {
  if(hexString==null || hexString.isEmpty()){
     return "";
  }
  if(hexString.length()%2 != 0){
    throw new Exception("String is not hex, length NOT divisible by 2: "+hexString);
  }
  int len = hexString.length();
  char[] output = new char[len+len/2];
  int i=0;
  int j=0;
  while(i<len){
      output[j++]='%';
      output[j++]=hexString.charAt(i++);
      output[j++]=hexString.charAt(i++);
  }
  return new String(output);
}

You'll need to convert the raw bytes to hexadecimal characters or whatever URL-friendly encoding they are using. Base32 or Base64 encodings are possible, but straight hexadecimal characters is the most common. URLEncoder is not needed for this string, because it shouldn't contain any characters that would require URL Encoding to %NN format.

The below will convert bytes for a hash (SHA-1, MD5SUM, etc) to a hexadecimal string:

/** Lookup table: character for a half-byte */
    static final char[] CHAR_FOR_BYTE = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};
         /** Encode byte data as a hex string... hex chars are UPPERCASE*/
         public static String encode(byte[] data){
             if(data == null || data.length==0){
                 return "";
             }
             char[] store = new char[data.length*2];
             for(int i=0; i<data.length; i++){
                 final int val = (data[i]&0xFF);
                 final int charLoc=i<<1;
                 store[charLoc]=CHAR_FOR_BYTE[val>>>4];
                 store[charLoc+1]=CHAR_FOR_BYTE[val&0x0F];
             }
             return new String(store);
         }

This code is fairly optimized and fast, and I am using it for my own SHA-1 byte encoding. Note that you may need to convert uppercase to lowercase with the String.toLowerCase() method, depending on which form the server accepts.

Answer 4

Use Apache Commons-Codec for all your encoding/decoding needs (except ASN.1, which is a pain in the ass)