Re: MD5 is slow

[Jeffrey Haas via NANOG <nanog () lists nanog org>]

> On Sep 8, 2025, at 3:26 AM, Vasilenko Eduard via NANOG <nanog () lists nanog org> wrote:
>
> Sorry. It looks like I was not clear enough. My question was not related to the discussed MD5 strength that occurred 
> during the last week.
> Public key is not needed very often, no need to pay attention to the speed of fingerprint generation.
> I was talking about Hash usage in many networking protocols, where it delays a network control plane message.

You'd have to be clearer about what protocol and what hash you're asking after.

Two of the common cases where such things show up is for authentication and for integrity checks.

For authentication in control protocols, the balance you're looking for is being able to do the operation fast enough 
for expected traffic load among all of the other work being done by the system.  If you're lucky, you might have 
hardware support for the cryptographic operation.  For control planes, sometimes it's just the router's general purpose 
CPU.  Easy examples of this sort of thing are the authentication fields for the IGPs, or for TCP-MD5/TCP-AO used by 
BGP, LDP, etc.

For integrity checks, you have a set of data you're trying to provide a short-hand as to whether it's been passed 
around intact.  You'll often see this for detached file signatures, although protocols may do similar things for 
internal checksum purposes as well.

Cryptography of any sort can be an attack on the device implementing it.  Use expensive ciphers and do volumetric 
attacks that cause that code to run, you'll burn CPU in some cases.  Most protocols try to do the cryptographic checks 
far down their validation procedures.

A regular conversation for BFD, as an example, is how often you want to do some bit of cryptography.  Line card CPUs 
are usually puny and MIGHT have access to some hardware support for common ciphers like MD5/SHA-1/SHA-2.  BFD sends 
tiny packets often some tens of ms apart.  Now scale that up to a potentially large number of session on a line card.  
Using better ciphers, if you want authentication (many don't) gets expensive, so there's need to potentially think 
differently about when you do it.  For example:

https://datatracker.ietf.org/doc/html/draft-ietf-bfd-optimizing-authentication

-- Jeff

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