Question

I have an caching application that uses a CRC64 value to ensure data integrity. I m thinking about putting an extra field, a timestamp to be passed around with the data between the various cache servers and compared to see if data has changed.

However, this requires protocol changes. While that s not a huge deal, I already have a CRC64 that could be used as an indicator that something has changed.

Does anyone know the stats around two blocks of data producing the same CRC64? If not, how could I compute it or estimate it s likelyhood?

Answer 1

如果您认为,第64条是完美的,那么这个数字是相当合理的:

碰撞概率为1%,需要6.1×10^8条目。碰撞概率为50%。

当然,如果数据可能由恶意来源提供,那么,由于震荡64很容易产生,因此,散射线中的碰撞可能十分猖獗。因此,你是否走这条路取决于输入数据的来源和碰撞的潜在影响。

Answer 2

两个given区块的碰撞概率为1/2⁶⁴,或1 % × 10¹⁹。

然而,如果你对N级人口碰撞速度感兴趣的话,这种可能性就会迅速增加。

For more information, see Birthday Problem on Wikipedia, which has formulas and approximations.

Answer 3

两个《儿童权利公约》64 相对于不同的随机数据而言是相同的,其可能性在2**64中几乎是一次。但是,由于《儿童权利公约》对数据模式有些敏感,可能会出现一些变性的情况,即你失去几个双亲保护命令。也许不可能出现硬数,但你在假设最坏的碰撞机会时可能不会安全,在2**50或50年时,这种机会将不足1。

如果你使用加密带而不是《儿童权利公约》64,那么你可以放心地接近理论限制,但一般而言,加密洗刷的成本要高得多。

友情链接