A cipher system for use by a sender and receiver provides a plaintext alphabet, each character of which is coded by a numerical synonym, the set of numerical synonyms comprising a collection of non-negative integers of common length and known to both sender and receiver. The system further provides a concatenation of the numerical synonyms comprising a plaintext message string integer corresponding to a plaintext message and a masking tape string integer comprising a randomly or pseudo-randomly accessed sequence of digits extracted from a string of digits accessible to both sender and receiver and added to the plaintext message string to form a ciphertext string. The numerical synonyms of plaintext alphabet characters may be permuted, relative to the normal listing of the alphabet, from message to message according to prior secret arrangement of sender and receiver. Also, the ciphertext string may be adulterated by prefixing, suffixing, or inserting integers of possibly variable length generated by a number generator, according to secret prior arrangement between sender and receiver. Still further, the ciphertext string may be subjected to permutations of blocks of its (adulterated) digits, according to secret prior arrangement between sender and receiver.