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From "Goldstein Lyor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SSHD-860) org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyIterator pre-loads client identities (private key files)
Date Tue, 06 Nov 2018 18:55:00 GMT

    [ https://issues.apache.org/jira/browse/SSHD-860?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16677170#comment-16677170

Goldstein Lyor commented on SSHD-860:

I do not necessarily agree with the severity but I can see why some may think it is not minor
(so upgraded it to major). Unfortunately, loading key pairs lazily is a major overhaul of
the code which we can afford at the moment given the extremely limited R&D resources at
our disposal. We have considered it in the past but I am not sure when we might find the time
for such an overhaul.

The good news is that we do accept code contributions (;)). If this is indeed critical for
you I recommend not to wait for us to get around to it, clone the code and publish a PR. (Again,
not because we don't want to, but because in the foreseeable future we might not be able to
invest the time it requires). If you do go ahead with it, please note that not only this class
needs an overhaul, but perhaps all the other identity loaders and all their code....

> org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyIterator pre-loads client identities
(private key files)
> ------------------------------------------------------------------------------------------------------------
>                 Key: SSHD-860
>                 URL: https://issues.apache.org/jira/browse/SSHD-860
>             Project: MINA SSHD
>          Issue Type: Bug
>    Affects Versions: 2.0.0, 2.1.0, 2.1.1
>            Reporter: Thomas Wolf
>            Priority: Major
> {{org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyIterator}} loads and caches in
memory private keys prematurely. Keys are loaded even if they are not used at all in the end.
In other words, incremental loading of keys doesn't work.
> This is bad for two reasons:
>  # Private keys should be kept in memory only if and when needed. Loading completely
unused private keys must be avoided.
>  # With encrypted private keys, the user may end up being asked for passphrases for keys
that are not used at all in the end, which is highly disruptive.
> {{org.apache.sshd.client.auth.pubkey.UserAuthPublicKeyIterator}} does in its constructor:
> {code:java}
> Iterator<? extends PublicKeyIdentity> current;
> Collection<Stream<? extends PublicKeyIdentity>> identities = new LinkedList<>();
> ...
> identities.add(Stream.of(ClientSession.providerOf(session))
>     .map(KeyIdentityProvider::loadKeys)
>     .flatMap(GenericUtils::stream)
>     .map(kp -> new KeyPairIdentity(signatureFactories, session, kp)));
> current = identities.stream().flatMap(r -> r).iterator();
> {code}
> The final {{current}} iterator uses some internal buffer (size unknown; didn't try to
determine it) and will pre-fill this buffer completely. So with buffer size _N_ it'll pre-load
the first _N_ keys from the combined identity stream. If the first key authenticates successfully,
loading all the others must not be done.
> See my [test case|https://github.com/tomaswolf/mina-sshd/blob/SSHD-860/sshd-core/src/test/java/org/apache/sshd/client/ClientKeyLoadTest.java]
showing this faulty behavior. It does exactly the same as the {{UserAuthPublicKeyIterator}} 
constructor, using two iterators with two identity files each, and then tests the resulting
iterator. The first {{hasNext()/next()}} call on the {{current}} iterator _loads all four

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