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From "Thomas Wolf (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SSHD-850) sshd client; encrypted private key identity file: FilePasswordProvider called only once; should be called NumberOfPasswordPrompts times
Date Wed, 17 Oct 2018 06:35:00 GMT

    [ https://issues.apache.org/jira/browse/SSHD-850?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16653046#comment-16653046
] 

Thomas Wolf commented on SSHD-850:
----------------------------------

I know the two are different, and one (keyboard-interactive auth) is handled fine by sshd.
The other (passphrases for encrypted private keys) isn't.

Your proposed work-around for the missing functionality (implement my own {{KeyPairProvider}}
that does this) implies that this special {{KeyPairProvider}} cannot use {{SecurityUtils.loadKeyPairIdentity()}}.
It even looks I'd have to implement a whole separate hierarchy of {{KeyPairResourceParser}}s
just to get something that in {{extractKeyPairs}} loops the required number of times, since
outside of that it is not known whether a failure to read a key was due to a wrong password
or some other problem. It also looks to me that I'd need a stateful {{FilePasswordProvider}}
that remembers if it had been called at all for the key so that I can query it – if it hasn't
even been called by the key parser, the key wasn't encrypted (or had a problem before we even
got to decrypting it) and re-trying would be futile. (Outside of {{extractKeyPairs}} it isn't
even known whether the key is encrypted at all.)

The fact that I'd have to side-step or re-implement quite a lot of the sshd default behavior
is to me an indication that something is missing here in sshd.

> sshd client; encrypted private key identity file: FilePasswordProvider called only once;
should be called NumberOfPasswordPrompts times
> ---------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: SSHD-850
>                 URL: https://issues.apache.org/jira/browse/SSHD-850
>             Project: MINA SSHD
>          Issue Type: Improvement
>    Affects Versions: 2.0.0
>            Reporter: Thomas Wolf
>            Priority: Minor
>
> In openssh, the ssh config entry NumberOfPasswordPrompts controls the number of times
the ssh client keeps asking for a password if the one entered was invalid in two cases:
>  # keyboard-interactive authentication, and
>  # asking for passwords for encrypted private keys in identity files in pubkey authentication
(see [openssh sources; sshconnect2.c|https://github.com/openssh/openssh-portable/blob/1a4a9cf/sshconnect2.c#L1380]).
> sshd-core only has support for (1) through setting the property {{ClientAuthenticationManager.PASSWORD_PROMPTS}}
in the session's properties.
> There doesn't seem to be any support for FilePasswordProvider to make it respect this
value.
> {{AbstractPEMResourceKeyPairParser.extractkeyPairs()}} and also {{BouncyCastleKeyPairResourceParser.loadKeyPair()}}
call {{FilePasswordProvider.getPassword()}} exactly once.
> So how can I write a ssh client using sshd that asks the user NumberOfPasswordPrompts
times? Either I'm missing something, or there is some support for this missing in sshd.



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