论文标题
chacha置换的旋转分析
Rotational analysis of ChaCha permutation
论文作者
论文摘要
我们表明，相对于旋转密码分析，Chacha20流密码的基本排列并不是最多17发回合的随机排列。特别是，我们为通过Chacha四分之一回合得出了旋转概率的较低和上限，我们展示了如何将界限扩展到完整的回合，然后再扩展到完整的排列。获得的边界表明，找到我们称为平行旋转碰撞的可能性，例如，17发chacha置换量的$ 2^{ - 488} $不到$ 2^{ - 488} $，而对于相同的输入大小的随机置换，此概率为$ 2^{ - 511} $。我们指出的是，我们的区分不是对Chacha20流密封器的攻击，而是从旋转隐性分析的角度对其内部置换的理论分析。
We show that the underlying permutation of ChaCha20 stream cipher does not behave as a random permutation for up to 17 rounds with respect to rotational cryptanalysis. In particular, we derive a lower and an upper bound for the rotational probability through ChaCha quarter round, we show how to extend the bound to a full round and then to the full permutation. The obtained bounds show that the probability to find what we call a parallel rotational collision is, for example, less than $2^{-488}$ for 17 rounds of ChaCha permutation, while for a random permutation of the same input size, this probability is $2^{-511}$. We remark that our distinguisher is not an attack to ChaCha20 stream cipher, but rather a theoretical analysis of its internal permutation from the point of view of rotational cryptanalysis.
