The Broadcast Encryption methods, often referred to as revocation schemes, allow data to be efficiently broadcast to a dynamically changing group of users. A special case is when the receivers are stateless [2,1]. Naor et al. [2] propose the Complete Subset Method (CSM) and the Subset Difference Method (SDM). Asano [1] puts forth two other methods, AM1 and AM2, which use public prime parameters to generate the decryption keys. The efficiency of broadcast encryption methods is measured by three parameters: (i) message size - the number of transmitted ciphertexts; (ii) storage at receiver - the number of private keys each receiver is required to store; and (iii) key derivation time - the computational overhead needed to access the decryption keys.
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