The authors discuss secure broadcasting, effected by means of a secure lock, on broadcast channels, such as satellite, radio, etc. This lock is implemented by using the Chinese Remainder theorem (CRT). The secure lock offers the following advantages: only one copy of the ciphertext is sent; the deciphering operation is efficient; and the number of secret keys held by each user is minimized. Protocols for secure broadcasting using the secure lock, based on the public-key cryptosystem as well as the private-key cryptosystem, are presented.>