Abstract: A computer-implemented method, which comprises: receiving an input message comprising N-bit input segments, N being an integer greater than one; converting the N-bit input segments into corresponding N-bit output segments using a 2N-by-2N one-to-one mapping stored in a non-transitory storage medium; and generating an output message comprising the N-bit output segments. Also, a computer-implemented method for a recipient to validate a message received from a sender, the message including a first part and a second part. This method comprises receiving a token from a witnessing entity; obtaining a first data element by joint processing of the first part of the message and the token; obtaining a second data element by joint processing of the second part of the message using a key associated with the sender; and validating the message by comparing the first and second data elements.