The Aumasson et al. paper also attacks ChaCha, achieving one round fewer: for 256 bits ChaCha6 with complexity 2139 and ChaCha7 with complexity 2248.
Aumasson et al. paper也攻击过ChaCha，实现了少一轮循环：256位ChaCha6有复杂性2139，ChaCha7有复杂性2248。