RE: MD5 is too fast

[nanog--- via NANOG <nanog () lists nanog org>]

Have you calculated how long it should take to test all 80-bit passwords? 200-bit passwords? 2000-bit passwords?

Suppose that a good server can try about a billion passwords per second. How long do you think it takes to try all the 
passwords?


On 11 September 2025 12:18:00 CEST, Vasilenko Eduard via NANOG <nanog () lists nanog org> wrote:
> The simple integer division on the processor takes something like 40 cycles (fast). Hence, the factorization challenge 
> should have thousands of bits. Then it is going to take millions of years for one processor to try all possibilities.
>
> If the password is just 12 letters (80 bits?), then the time to test the password should be longer. Or else the good 
> processor would try all combinations for a limited time.
> Of course, a longer password would help a lot, but even 200 bits is not 2000. The check should be proportionally 
> slower.
> It is especially a problem when we are dealing with predictable passwords based on human language words.
>
> Maybe SHA-2/3 have not been developed with "slowness" as a goal. It may be that only randomness was the target. Hence, 
> so many assembler instructions for one round.
> But only the slowness permits its use for HMAC or the password fingerprint that you have discussed before.
> I could not believe that slowness is just a byproduct of randomness. It is so evident why it is needed by itself (for 
> some applications).
> Ed/
> -----Original Message-----
> From: Thomas Bellman via NANOG <nanog () lists nanog org> 
> Sent: Thursday, September 11, 2025 12:03
> To: North American Network Operators Group <nanog () lists nanog org>
> Cc: Thomas Bellman <bellman () nsc liu se>
> Subject: Re: MD5 is slow
>
> On 2025-09-11 09:23, Vasilenko Eduard via NANOG wrote:
>
> > SHA-2 and SHA-3 are used not only for networking, they are general.
> > Hence, they were developed to be slow enough to prevent brute force 
> > for some other applications.
>
> Since you are asserting that the hash functions must be "slow" in order to resist brute force attacks, could you 
> perhaps give us an estimate of *how* slow they must be?  And how you arrive at that (e.g. how much resources does the 
> attacker deploy, and how long walltime do you give the attacker)?
>
>
>       /Bellman
>
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