Re: MD5 is slow

[Saku Ytti via NANOG <nanog () lists nanog org>]

I didn't read the paper in detail, but it is immaterial if the paper
finds performance lacking in some architecture. We are not discussing
what is the performance, we are discussing what is the design goal.
Design goal is that it should be fast.
Here is another SHA3 paper which looks at low, mid, high performance.
cores and hardware implementations and reports massively faster SHA3
performance. https://keccak.team/files/Keccak-implementation-3.2.pdf

My cursory look at SHA2 I came up thinking that a typical +10y old
XEON will do like 10-20cpb, and <10y will do 1-2cpb (when using SHA
instruction set). Which is not meaningful contributor to latency and
indeed we can amortize this if we are on microseconds budget, as we
can do other work while we validate it, before committing to one or
another outcome.

https://www.cs.haifa.ac.il/~orrd/HashFuncSeminar/Lecture13.pdf - here
are SHA3 finalist performances:
Skein 4-8cpb
Blake 5-10cpb
KECCAK 14-16cpb
Grøstl 15-35cpb
JH 16-45cpb

They are not low, because the authors were incompetent. They are both
memory and instruction count cheap by design. If you find anecdotes of
performances that you consider slow, it doesn't change the fact that
the design goal is cheap cycles, cheap memory.

Look for argon2, balloon with design goals which would be more
conducive towards hashing 8byte passwords.




On Wed, 10 Sept 2025 at 09:55, Vasilenko Eduard
<vasilenko.eduard () huawei com> wrote:
> Hi Ytti, I have to apologize for the subject. I have SHA2/3 in mind because NIST said that MD5 is "not recommended".
> I have answered Matthew, but it was blocked by the mailman. This answer is very relevant to you too:
>
> Hi Matthew,
> Thanks for the discussion. It is the right approach to calculate carefully.
> I do not believe that MD5 is a good basis; NIST recommends moving away from it. I am not qualified to question NIST 
> decisions.
> I have already pointed out the reference to https://www.ijcna.org/Manuscripts/IJCNA-2020-O-01.pdf . It is SHA-3; I 
> have not found good data for SHA-2 (I was interested in ARM).
> They have a table in section 6.1 for all sizes. It is 4151199 Cycles for 750B. The maximum clock for the ARM core is 
> about 2Ghz (practically less, routers do not have enough cooling for this). Hence, this 750B would be checked for 2ms.
> There is a discussion in the IETF that in the big networks, many attributes (TE, flex-algo, whatever) are attached in 
> ISIS, hence the packet may be full size (1500B). Then the hash would be 4ms.
> Twice (8ms) if the message is relayed, because a hash would be needed on input and output.
>
> Hence, I do not understand why 5ms is “completely incorrect”.
> Eduard
> -----Original Message-----
> From: Saku Ytti <saku () ytti fi>
> Sent: Wednesday, September 10, 2025 09:39
> To: North American Network Operators Group <nanog () lists nanog org>
> Cc: Vasilenko Eduard <vasilenko.eduard () huawei com>
> Subject: Re: MD5 is slow
>
> On Wed, 10 Sept 2025 at 09:12, Vasilenko Eduard via NANOG <nanog () lists nanog org> wrote:
>
> > But it's reality. Many passwords are not strong enough.
> > More importantly, hash has XX rounds to give a really random output.
> > Hence, the hash is designed to be slow.
>
> No, not all hashes, only hashes for some application for some reason.
> MD5, SHA are designed to be fast. You can look into SHA competition and see that CPB is a metric which they are 
> measured against. They have to be fast in the existing instruction set and they have to be friendly towards HW 
> acceleration to win SHA competition.
>
> You really need to look at your application before you start to define what metrics hash should and should not have.
>
> Yes, for password hashing (like legacy unix 8 bytes) MD5 was a poor choice.
>
> For authenticating ISIS, BGP whatever, there is absolutely no reason for it to be slow. In the above example you need 
> collision, any input string will be accepted. For BGP MD5, TCP-AO, it is authenticating the _message_, not only you 
> need collision, but you need the input to be valid and conducive towards your attack vector.
>
> I continue to be at loss, this thread has made these points repeatedly. It is also easy to verify out of the thread 
> that you are not being misled when you are told being slow is not only a non-goal but undesirable for most hash use 
> cases. And there are many hash use cases, your programming language needs hash to do associative arrays, your switch 
> needs hash to do ECMP (which is interesting topic onto itself, as we used to use same CRC as for ethernet FCS, which 
> turns out to be not good hash for ECMP).
>
>
>
> --
>   ++ytti



-- 
  ++ytti
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