The technologically more advanced BSB D-MAC/EuroCypher system was gradually replaced with Sky's VideoCrypt video encryption system.
The system also included a cryptographic element called the Fiat Shamir Zero Knowledge Test.
Already in use in America since 1997, the VideoGuard system was introduced to the UK by NDS in 1998 with the launch of Sky Digital, replacing the VideoCrypt system (also supplied by NDS) in use on Sky's analogue broadcasts.
Later on 3 June 1990, it started using transponder 24 on Astra 1B, at frequency 11.567 MHz for 11 hours a day, using the Videocrypt II encryption (time-sharing with The Children's Channel and later with CMT Europe).