Freestyle，一个随机版本的ChaCha，用于抵抗离线暴力攻击和字典式攻击
Freestyle, a randomized version of ChaCha for resisting offline brute-force and dictionary attacks
摘要：
介绍了ChaCha密码的一种随机可变轮的Freestyle。Freestyle使用基于哈希的停止条件的概念，其中使用不正确密钥的解密尝试可能需要更长的时间才能停止。这使得Freestyle能够抵抗密钥猜测攻击，即暴力攻击和基于字典的攻击。Freestyle证明了一种新的方法，通过使用随机数的轮为每个块的密文随机化，其中确切的轮数是未知的接收器提前。Freestyle提供了为给定密钥、随机数和消息生成$2^{128}$不同密文的可能性，从而抵抗密钥和随机数重用攻击。由于其固有的随机行为，Freestyle使得通过已知明文、选择明文和选择密文攻击的密码分析在实践中变得困难。另一方面，Freestyle的密码初始化过程更昂贵，通常会生成3.125%的密文，并且被发现比ChaCha20慢1.6到3.2倍。Freestyle适用于在性能和密文大小方面更倾向于密文随机化以及抵抗密钥猜测和密钥重用攻击的应用程序。Freestyle非常适合于假设密文完全由对手控制的应用程序，并且可以进行离线密钥猜测攻击。
英文摘要：
This paper introduces Freestyle, a randomized and variable round version of the ChaCha cipher. Freestyle uses the concept of hash based halting condition where a decryption attempt with an incorrect key is likely to take longer time to halt. This makes Freestyle resistant to key-guessing attacks i.e. brute-force and dictionary based attacks. Freestyle demonstrates a novel approach for ciphertext randomization by using random number of rounds for each block, where the exact number of rounds are unknown to the receiver in advance. Freestyle provides the possibility of generating $2^{128}$ different ciphertexts for a given key, nonce, and message; thus resisting key and nonce reuse attacks. Due to its inherent random behavior, Freestyle makes cryptanalysis through known-plaintext, chosen-plaintext, and chosen-ciphertext attacks difficult in practice. On the other hand, Freestyle has costlier cipher initialization process, typically generates 3.125% larger ciphertext, and was found to be 1.6 to 3.2 times slower than ChaCha20. Freestyle is suitable for applications that favor ciphertext randomization and resistance to key-guessing and key reuse attacks over performance and ciphertext size. Freestyle is ideal for applications where ciphertext can be assumed to be in full control of an adversary, and an offline key-guessing attack can be carried out.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
