PuTTY wish hostkey-prefer-cached

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summary: PuTTY should prefer host-key types it already has cached
class: wish: This is a request for an enhancement.
priority: high: This should be fixed in the next release.
fixed-in: 2015-05-30 d21041f7f8846b16ff6d72ed696d6190627e19b4 (0.68)

We've just added support for several new host key formats (ECDSA; Ed25519) for the first time in a long time. EC host keys are already widely deployed in servers. If we do nothing, this is going to lead to lots of users prompted for host key verification as if they were connecting to the server for the first time.

PuTTY now deliberately adjusts its algorithm preferences to prefer host key types that it already has in its cache. This means that in any case where pre-EC PuTTY would have successfully connected without issuing a host-key prompt, post-EC PuTTY will do the same (using the existing host key it knows rather than any new EC key; automatically upgrading is a knotty problem covered by host-key-rollover).

Update, March 2016: in this situation, it's now possible to upgrade to a newer host key manually, using the new "Cache new host key type" submenu on the Special Commands menu.

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Audit trail for this wish.

(last revision of this bug record was at 2017-04-28 16:52:45 +0100)