[jira] [Commented] (SSHD-1216) Implement RFC 8332 server-sig-algs on the server

["Evgeny Pasynkov (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SSHD-1216?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17429222#comment-17429222 ] 

Evgeny Pasynkov commented on SSHD-1216:
---------------------------------------

For me works this snippet at application side, no need to patch library:

```

mySSHD.kexExtensionHandler = object : KexExtensionHandler {
 val extensionsSentKey = AttributeRepository.AttributeKey<Unit>()

 override fun isKexExtensionsAvailable(session: Session, phase: KexExtensionHandler.AvailabilityPhase): Boolean {
 return phase == KexExtensionHandler.AvailabilityPhase.NEWKEYS
 }

 override fun sendKexExtensions(session: Session, phase: KexExtensionHandler.KexPhase) {
 if (phase != KexExtensionHandler.KexPhase.NEWKEYS)
 return

 if (session.getAttribute(extensionsSentKey) != null)
 return

 session.addSessionListener(object : SessionListener {
 override fun sessionEvent(session: Session, event: SessionListener.Event) {
 if (event == SessionListener.Event.KeyEstablished) {
 val buffer: Buffer = session.createBuffer(KexExtensions.SSH_MSG_EXT_INFO)
 buffer.putInt(1) // Number of extensions
 ServerSignatureAlgorithms.INSTANCE.putExtension(session.signatureFactories.map \{ it.name }, buffer)
 session.writePacket(buffer)

 session.setAttribute(extensionsSentKey, Unit)
 session.removeSessionListener(this)
 }
 }
 })
 }
}

```

> Implement RFC 8332 server-sig-algs on the server
> ------------------------------------------------
>
>                 Key: SSHD-1216
>                 URL: https://issues.apache.org/jira/browse/SSHD-1216
>             Project: MINA SSHD
>          Issue Type: Improvement
>            Reporter: Ben Humphreys
>            Priority: Major
>
> In the recently released [OpenSSH 8.8|https://www.openssh.com/txt/release-8.8] for RSA keys the public key signature algorithm that depends on SHA-1 has been disabled by default:
> {quote}This release disables RSA signatures using the SHA-1 hash algorithm 2by default. This change has been made as the SHA-1 hash algorithm is cryptographically broken, and it is possible to create chosen-prefix 4hash collisions for <USD$50K [1]
> {quote}
> As a result OpenSSH 8.8 clients are unable to authenticate with Mina SSHD servers with RSA based keys (it is however possible to reenable ssh-rsa). OpenSSH since 7.2 does however support RFC 8332 RSA/SHA-256/512 signatures, indeed the release notes go on to say:
> {quote}
> For most users, this change should be invisible and there is no need to replace ssh-rsa keys. OpenSSH has supported RFC8332 RSA/SHA-256/512 signatures since release 7.2 and existing ssh-rsa keys will automatically use the stronger algorithm where possible.
> {quote}
> It appears Mina SSHD partly implements support for RFC 8332, indeed the client code appears to support it (see SSHD-1141). However the server appears to lack full support because it doesn't full implement the"server-sig-algs" extension.
> The basic framework for supporting this seems to be present, specifically {{AbstractKexFactoryManager.setKexExtensionHandler()}} could perhaps permit such a "server-sig-algs" extension.
>  



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