code: function (password, ciphertext, params, rp) {
      var j = sjcl.json;
      return j._decrypt(password, j.decode(ciphertext), params, rp);
    }
docs: Simple decryption function.
  @param {String|bitArray} password The password or key.
  @param {String} ciphertext The ciphertext to decrypt.
  @param {Object} [params] Additional non-default parameters.
  @param {Object} [rp] A returned object with filled parameters.
  @return {String} The plaintext.
  @throws {sjcl.exception.invalid} if a parameter is invalid.
  @throws {sjcl.exception.corrupt} if the ciphertext is corrupt.