Possible one byte Xor keys

Question

I need to find a key to decrypt something that was encrypted with Xor. I know that the key is only one byte. I was hoping to be able to brute force guess the correct key. Is there a list of possible keys someone could direct me to. Also, would the key be in hex or decimal. Thanks

Answer 1

Well, if the key is just one byte, then just try all numbers from 0 (0000 0000) to 255 (1111 1111)

Answer 2

I provided an answer previously for some 8-channel xor encryption scheme producing a result from an encoded msg and no keys. The function that finds the key along with setup and support code is as follows:

//setup a table of readable characters (characters we will expect to see in the decrypted result).
var readableCharacters=Object.create(null);
var alphanumerics=[[0x30,0x39],[0x41,0x5a],[0x61,0x7a]];
var alphabetical=[[0x41,0x5a],[0x61,0x7a]];
alphanumerics.forEach(function(range){
  var indexStart=range[0];
  var indexEnd=range[1];
  for (var i=indexStart; i<=indexEnd; i++){
    var ch=String.fromCharCode(i);
    readableCharacters[ch]=1;
  }   
});
//add some extra characters to the table (optional)
(" ,.;:!\"'").split("").forEach(function(ch){readableCharacters[ch]=1;});

//xor decryption
function dec(nkey,ncrypt){
  var ndec=nkey^ncrypt;
  return ndec;
}

//find a key candidate by determining which keys correspond to the highest occurance of characters found in the readable character lookup table.
function findKeyCandidate(byteArray){
  var keyResults=[];
  for (var key=0; key<256; key++){
    keyResults[key]=0;
    byteArray.forEach(function(ncrypt){
      var ndec=dec(key,ncrypt);
      var dchar=String.fromCharCode(ndec);
      if(readableCharacters[dchar]){
        keyResults[key]++;
      }
    });
  }
  keyResults=keyResults.map(function(count,index){
    return {key:index,count:count};
  });
  keyResults.sort(function(a,b){
    return a.count-b.count;
  });
  return keyResults.pop().key;
}

Note: For the input you'll need an actual byte array (i.e. an array of numbers 0-255) not a hexadecimal string (the conversion from hex to byte array and back is present in the previous solution linked above). Output is a byte-size key.

This all assumes you'll end up with a message that is readable by humans, if you expect some other message structure/composition, then you'll need to modify the code according to what you expect to find.