The one-time pad is the only encryption technique that has been mathematically proven to be uncrackable. While hard to use, it has often been the choice for highly sensitive traffic. Soviet spies used one-time pads in the 1940s and -50s. The Washington-Moscow “hot line” also uses one-time pads. However, the technique is hard to use correctly.
Whenever your browser establishes a “secure” connection to a web site, it encrypts the data. The encryption often takes place byte-by-byte, since the software can’t always predict how much data will be sent. This encryption style requires a stream cipher.