[Cryptography] hash size

jamesd at echeque.com jamesd at echeque.com
Thu Nov 1 03:23:30 EDT 2018

> On 10/31/2018 12:11 PM, jamesd at echeque.com wrote:
>> With 128 bits, a birthday attack is just barely possible, in that
>> someone could search 2^64 examples, but, supposing you don't care about
>> birthday attacks, only about someone finding a pre-image or finding a
>> new value that gives the same hash as someone else's hash, what do you get?

On 2018-11-01 07:10, Ray Dillinger wrote:
> "Just barely possible?"  Unless it's a hash that's specifically made to
> be inefficient to compute, then searching 2^64 examples is something
> that can be done in a couple of days on a single server rack.

You are not searching 2^64 examples against a single bit pattern.

You are searching 2^64 examples against 2^64 examples.

So, a single server rack with thirty million sixteen terabyte hard disks.

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