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Digital multimedia content is delivered to homes via the Internet, satellite, terrestrial and cable networks. Scrambling is a common approach used by conditional access systems to prevent unauthorized access to audio/visual data. The descrambling keys are securely distributed to the receivers in the same transmission channel. Their protection is an important part of the key management problem. Although public-key cryptography provides a viable solution, alternative methods are sought for economy and efficiency. Message authentication is an important objective of information security in modern electronic distribution networks. This objective is met by providing the receiver of a message an assurance of the sender's identity. As physical protection such as sealed envelopes is not possible for messages expressed as binary sequences, digital tools have been developed using cryptography. A major limitation of all cryptographic methods for message authentication lies in their use of algorithms with fixed symmetric or public keys. This paper presents a key transport protocol based on secret sharing. Conditional access and message authentication are two important application areas for which the advantages of the proposed protocol are discussed. The protocol eliminates the need for a cipher, yet effectively combines the advantages of symmetric and public-key ciphers. It can be used to build a new key management scheme that allows the service providers to generate different keys for different sets of receivers, and to renew these keys in a convenient way.