Abstract: An encryption system for transmitting confidential data from a transmitting device comprising: a processor fore effecting a dynamic algorithm which is a function of time, e.g., Greenwich Mean Time; means for entering confidential data into the transmitting device; means for encrypting at least a portion of said confidential data in accordance with said algorithm; means for transmitting the resulting encrypted data; means for decrypting the received data, including circuitry which embodies the inverse of said dynamic function; means for extracting said confidential data from the encrypted data in accordance with said inverse dynamic algorithm. The system is intended to be used for electronic funds transfers: e.g., for credit card transactions.