A method and device for creating ciphertext from plaintext, and for decoding ciphertext, utilizing a tree structure for both encoding and decoding, the tree having leaves which are associated with plaintext symbols and the branches having assigned thereto a member of the ciphertext alphabet so that when encoding, a traversal is made between the root and the leaf corresponding to the plaintext and recording the ciphertext associated with each branch traversed, and when decoding, using the ciphertext to determine the branches to be traversed until a leaf is reached and recording the plaintext associated with that leaf.