如果从 1 数到 X，其中 X 是第一个与前一个数字发生 md5 冲突的数字，那么 X 是哪个数字？
我想知道如果我使用 md5 作为序列号，在发生冲突之前我可以期望能够枚举多少个单元。
Theoretically, you can expect collisions for X around 264. For a hash function with an output of n bits, first collisions appear when you have accumulated about 2n/2 outputs (it does not matter how you choose the inputs; sequential integer values are nothing special in that respect).
Of course, MD5 has been shown not to be a good hash function. Also, the 2n/2 is only an average. So, why don't you try it ? Take a MD5 implementation, hash your serial numbers, and see if you get a collision. A basic MD5 implementation should be able to hash a few million values per second, and, with a reasonable hard disk, you could accumulate a few billions of outputs, sort them, and see if there is a collision.
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