Abstract: 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.

Abstract: 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.

Abstract: A process for identifying the original tree, which is a member of a dictionary of labelled ordered trees, by processing a potentially Noisy Subsequence-Tree. The original tree relates to the Noisy Subsequence-Tree through a Subsequence-Tree, which is an arbitrary subsequence-tree of the original tree, which is further subjected to substitution, insertion and deletion errors yielding the Noisy Subsequence-Tree. This invention has application to the general area of comparing tree structures which is commonly used in computer science, and in particular to the areas of statistical, syntactic and structural pattern recognition.