On Tue, 30 Apr 2024, Philip Homburg wrote:
The advise is split between producing SHA1 signatures and consuming SHA1
signatures, and those timings do not have to be identical.
That said, a number of OSes have already forced the issue by failing
SHA1 as cryptographic operation (RHEL, CentOS, Fedora, maybe more). So
right now, if you run DNSSEC with SHA1 (which includes NSEC3 using
SHA1), your validator might already return it as an insecure zone.
I think a MUST NOT for signing with SHA1 is a no-brainer. The timing for
MAY on validation should be relatively short (eg 0-2 years?)
What worries me about the draft is the security section. I can understand
the desire to get rid of old crypto, but as far as I can tell
this draft will mostly decrease security.
It will also prevent ServFails when the system crypto SHA1 for
authentication and signature purposes is blocked, and the DNS software
sees this as a failure and returns BOGUS. I am not sure how many DNS
implementations are now probing SHA1 and on failure put it in the
"unsupported algorithm" class, to serve it as insecure instead of bogus.
This issue did hit RHEL,CentOS, Fedora.
We can accept as given that it is easy to find collisions for SHA1. However,
a second pre-image attack is way off in the future.
I'm not too concerned about that.
Looking at the signer part, this is not great either. Moving away from SHA1
requires an algorithm roll-over. DNSSEC is already quite fragile and algorithm
rolls are worse. So there is a failure risk that is too big ignore.
Yes, this fragility is why there are still zones using SHA1 at all. But
I think software and DNS services have no matured to the point where it
is save to do. Eg bind, opendnssec, knot.
This draft requires zones that do not have a collision risk to move to a
different algorithm, at a significant risk, but there is no increase in
security. So that part is also a net negative for security.
Staying at SHA1 incurs the above risk of SHA1 leading to Bogus/ServFail.
So it seems that we are asked to adopt a draft that will mostly reduce
security, not increase it.
It prevents zone outages.
There might be other arguments for adopting the draft, such a Redhat not
validating signatures with SHA1 anymore. But those arguments are not
mentioned in the draft.
I guess these considerations can be added to the draft if the WG wants?
And if some companies from one country want to shoot themselves in the foot,
does the rest of the world have to follow?
The IETF and its cryptographic policies are a careful interworking
between market forces, reality and desire. Moving to fast leads to RFCs
being ignored. Moving too slow means RFCs do not encourage
modernization. Every other protocol has left SHA1 behind. It's time for
DNS to follow suit. It's had its "exemption" for a few years already.
Paul
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