A fast software one-way hash function
Journal of Cryptology
Improving Implementable Meet-in-the-Middle Attacks by Orders of Magnitude
CRYPTO '96 Proceedings of the 16th Annual International Cryptology Conference on Advances in Cryptology
Design Principles for Dedicated Hash Functions
Fast Software Encryption, Cambridge Security Workshop
TWOPRIME: A Fast Stream Ciphering Algorithm
FSE '97 Proceedings of the 4th International Workshop on Fast Software Encryption
Secure and Private Distribution of Online Video and Some Related Cryptographic Issues
ACISP '01 Proceedings of the 6th Australasian Conference on Information Security and Privacy
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Ding et al [DNRS97] propose a stream generator based on several layers. We present several attacks. First, we observe that the non-surjectivity of a linear combination step allows us to recover half the key with minimal effort. Next, we show that the various bytes are insufficiently mixed by these layers, enabling an attack similar to those on two-loop Vigenere ciphers to recover the remainder of the key. Combining these techniques lets us recover the entire TWOPRIME key. We require the generator to produce 233 blocks (235 bytes), or 19 hours worth of output, of which we examine about one million blocks (223 bytes); the computational workload can be estimated at 228 operations. Another set of attacks trades off texts for time, reducing the amount of known plaintext needed to just eight blocks (64 bytes), while needing 232 time and 232 space. We also show how to break two variants of TWOPRIME presented in the original paper.