Movable Type Scripts

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TEA (Tiny Encryption Algorithm)

128 bits (16 characters) from the Password will be used to encrypt the Plaintext, using Wheeler & Needham’s Tiny Encryption Algorithm (‘xtea’).

The more recent Block TEA is simpler and more effective, especially for arbitrary-length strings.

See below for the source code of the JavaScript implementation. You are welcome to re-use these scripts [without any warranty express or implied] provided you retain my copyright notice and when possible a link to my website. If you have any queries or find any problems, please contact me.
© 2000-2005 Chris Veness

// use (16 chars of) 'password' to encrypt 'plaintext'

function encrypt(plaintext, password) {
  var v = new Array(2), k = new Array(4), s = "", i;

  plaintext = escape(plaintext);  // use escape() so only have single-byte chars to encode

  // build key directly from 1st 16 chars of password
  for (var i=0; i<4; i++) k[i] = Str4ToLong(password.slice(i*4,(i+1)*4));

  for (i=0; i<plaintext.length; i+=8) {  // encode plaintext into s in 64-bit (8 char) blocks
    v[0] = Str4ToLong(plaintext.slice(i,i+4));  // ... note this is 'electronic codebook' mode
    v[1] = Str4ToLong(plaintext.slice(i+4,i+8));
    code(v, k);
    s += LongToStr4(v[0]) + LongToStr4(v[1]);
  }

  return escCtrlCh(s);
  // note: if plaintext or password are passed as string objects, rather than strings, this
  // function will throw an 'Object doesn't support this property or method' error
}

// use (16 chars of) 'password' to decrypt 'ciphertext' with xTEA

function decrypt(ciphertext, password) {
  var v = new Array(2), k = new Array(4), s = "", i;

  for (var i=0; i<4; i++) k[i] = Str4ToLong(password.slice(i*4,(i+1)*4));

  ciphertext = unescCtrlCh(ciphertext);
  for (i=0; i<ciphertext.length; i+=8) {  // decode ciphertext into s in 64-bit (8 char) blocks
    v[0] = Str4ToLong(ciphertext.slice(i,i+4));
    v[1] = Str4ToLong(ciphertext.slice(i+4,i+8));
    decode(v, k);
    s += LongToStr4(v[0]) + LongToStr4(v[1]);
  }

  // strip trailing null chars resulting from filling 4-char blocks:
  s = s.replace(/\0+$/, '');

  return unescape(s);
}


function code(v, k) {
  // Extended TEA: this is the 1997 revised version of Needham & Wheeler's algorithm
  // params: v[2] 64-bit value block; k[4] 128-bit key
  var y = v[0], z = v[1];
  var delta = 0x9E3779B9, limit = delta*32, sum = 0;

  while (sum != limit) {
    y += (z<<4 ^ z>>>5)+z ^ sum+k[sum & 3];
    sum += delta;
    z += (y<<4 ^ y>>>5)+y ^ sum+k[sum>>>11 & 3];
    // note: unsigned right-shift '>>>' is used in place of original '>>', due to lack
    // of 'unsigned' type declaration in JavaScript (thanks to Karsten Kraus for this)
  }
  v[0] = y; v[1] = z;
}

function decode(v, k) {
  var y = v[0], z = v[1];
  var delta = 0x9E3779B9, sum = delta*32;

  while (sum != 0) {
    z -= (y<<4 ^ y>>>5)+y ^ sum+k[sum>>>11 & 3];
    sum -= delta;
    y -= (z<<4 ^ z>>>5)+z ^ sum+k[sum & 3];
  }
  v[0] = y; v[1] = z;
}


// supporting functions

function Str4ToLong(s) {  // convert 4 chars of s to a numeric long
  var v = 0;
  for (var i=0; i<4; i++) v |= s.charCodeAt(i) << i*8;
  return isNaN(v) ? 0 : v;
}

function LongToStr4(v) {  // convert a numeric long to 4 char string
  var s = String.fromCharCode(v & 0xFF, v>>8 & 0xFF, v>>16 & 0xFF, v>>24 & 0xFF);
  return s;
}

function escCtrlCh(str) {  // escape control chars which might cause problems with encrypted texts
  return str.replace(/[\0\t\n\v\f\r\xa0'"!]/g, function(c) { return '!' + c.charCodeAt(0) + '!'; });
}

function unescCtrlCh(str) {  // unescape potentially problematic nulls and control characters
  return str.replace(/!\d\d?\d?!/g, function(c) { return String.fromCharCode(c.slice(1,-1)); });
}