Cryptanalysis of Stream Cipher Alpha1
Komninos, Honary and Darnell recently proposed stream cipher Alpha1. Alpha1 is based on A5/1 and is claimed to be much safer than A5/1. However Alpha1 is insecure: a 29-bit feedback shift register could be recovered with about 3000 known plaintext bits with O(229) operations. The rest of the message could be recovered in the broadcast application in which the same message is encrypted with different keys.
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