Elliptic Curve cryptography for public key authentication

[termim]

Once I connect to some host that supplies its public key in ecdsa I can't use twisted's conch.ssh anymore. It always raises BadKeyError:

2011-11-01 13:35:46-0400 [-] Log opened.
2011-11-01 13:35:46-0400 [-] Starting factory <twisted.conch.client.direct.SSHClientFactory instance at 0x105bf80>
2011-11-01 13:35:46-0400 [SSHClientTransport,client] kex alg, key alg: diffie-hellman-group-exchange-sha1 ssh-rsa
2011-11-01 13:35:46-0400 [SSHClientTransport,client] outgoing: aes256-cbc hmac-sha1 none
2011-11-01 13:35:46-0400 [SSHClientTransport,client] incoming: aes256-cbc hmac-sha1 none
2011-11-01 13:35:47-0400 [SSHClientTransport,client] Unhandled Error
	Traceback (most recent call last):
	  File "/usr/lib64/python2.7/site-packages/twisted/python/log.py", line 84, in callWithLogger
	    return callWithContext({"system": lp}, func, *args, **kw)
	  File "/usr/lib64/python2.7/site-packages/twisted/python/log.py", line 69, in callWithContext
	    return context.call({ILogContext: newCtx}, func, *args, **kw)
	  File "/usr/lib64/python2.7/site-packages/twisted/python/context.py", line 118, in callWithContext
	    return self.currentContext().callWithContext(ctx, func, *args, **kw)
	  File "/usr/lib64/python2.7/site-packages/twisted/python/context.py", line 81, in callWithContext
	    return func(*args,**kw)
	--- <exception caught here> ---
	  File "/usr/lib64/python2.7/site-packages/twisted/internet/selectreactor.py", line 146, in _doReadOrWrite
	    why = getattr(selectable, method)()
	  File "/usr/lib64/python2.7/site-packages/twisted/internet/tcp.py", line 460, in doRead
	    rval = self.protocol.dataReceived(data)
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/ssh/transport.py", line 438, in dataReceived
	    self.dispatchMessage(messageNum, packet[1:])
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/ssh/transport.py", line 453, in dispatchMessage
	    f(payload)
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/ssh/transport.py", line 1182, in ssh_KEX_DH_GEX_REPLY
	    d = self.verifyHostKey(pubKey, fingerprint)
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/client/direct.py", line 87, in verifyHostKey
	    fingerprint)
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/client/default.py", line 74, in verifyHostKey
	    or os.path.expanduser("~/.ssh/known_hosts")
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/client/knownhosts.py", line 417, in fromPath
	    entry = HashedEntry.fromString(line)
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/client/knownhosts.py", line 253, in fromString
	    stuff, keyType, key, comment = _extractCommon(string)
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/client/knownhosts.py", line 59, in _extractCommon
	    key = Key.fromString(keyString.decode('base64'))
	  File "/usr/lib64/python2.7/site-packages/twisted/conch/ssh/keys.py", line 81, in fromString
	    raise BadKeyError('cannot guess the type of %r' % data)
	twisted.conch.ssh.keys.BadKeyError: cannot guess the type of '\x00\x00\x00\x13ecdsa-sha2-nistp256\x00\x00\x00\x08nistp256\x00\x00\x00A\x04j\x82Z\x88v\xad\xf9\xa3\xc4\x94\x19\xff\xc5\x81\x0e6\x7f\xaf\xce\xf5\xbbC\x1d\x8f\x99l\x99=\x95\xc9\x1f\x1e{\xb0\xb7:Z\x9fh7\x91\xa8lf\x03\xc2`x\x05\x1a\xadqV\x0f|\xa7 `2\x80\xda\x0f\x8e\x11'
	
2011-11-01 13:35:47-0400 [SSHClientTransport,client] connection lost
2011-11-01 13:35:47-0400 [SSHClientTransport,client] Stopping factory <twisted.conch.client.direct.SSHClientFactory instance at 0x105bf80>

[Jean-Paul Calderone]

The regular-releases milestone is for release automation related tasks.

[Ying Li]

I filed #5530 recently, which may be related (or possibly a duplicate)

[Thijs Triemstra]

parse ECDSA

[Thijs Triemstra]

Attached test script generates a ValueError on an ECDSA private key:

$ ssh-keygen -b 521 -t ecdsa -f id_ecdsa_conch -N qwerty
Generating public/private ecdsa key pair.
Your identification has been saved in id_ecdsa_conch.
Your public key has been saved in id_ecdsa_conch.pub.
The key fingerprint is:
9c:36:91:fd:d5:f9:ee:92:55:65:49:3d:0a:d6:2a:8c 

The key's randomart image is:
+--[ECDSA  521]---+
|            . ..o|
|         o o . +=|
|        = o o oo+|
|       E = o o  o|
|        S . .   o|
|       . .     ..|
|               o.|
|              o. |
|               ..|
+-----------------+

$ python ecdsa.py id_ecdsa_conch qwerty

Traceback (most recent call last):
  File "ecdsa.py", line 13, in <module>
    key = Key.fromFile(fn, passphrase=phrase)
  File "/home/thijs/workspaces/opensource/software/twisted/svn/Twisted/trunk/twisted/conch/ssh/keys.py", line 62, in fromFile
    return Class.fromString(file(filename, 'rb').read(), type, passphrase)
  File "/home/thijs/workspaces/opensource/software/twisted/svn/Twisted/trunk/twisted/conch/ssh/keys.py", line 90, in fromString
    return method(data, passphrase)
  File "/home/thijs/workspaces/opensource/software/twisted/svn/Twisted/trunk/twisted/conch/ssh/keys.py", line 216, in _fromString_PRIVATE_OPENSSH
    keyData = DES3.new(decKey, DES3.MODE_CBC, iv).decrypt(b64Data)
ValueError: IV must be 8 bytes long

Replying to cyli:

I filed #5530 recently, which may be related (or possibly a duplicate)

Can you try the attached script with your key?

[termim]

Actually there are two bugs here

1. missing support for ecdsa keys
2. bug when reading knownhosts file

For the second a simpler one case I've opened another ticket #5616 (with a patch attached).

[z3p]

Can you attach an ECDSA key? I couldn't create one on OS X or on Debian.

[Thijs Triemstra]

private

[Thijs Triemstra]

public

[Thijs Triemstra]

Attached the keys, generated like described in comment 4.

[z3p]

(In [34683]) Branching to 'ecdsa-keys-5350'

[z3p]

(In [34684]) add ECDSA key guessing

Refs #5350

[z3p]

Unfortunately at the moment, PyCrypto doesn't support ECDSA keys. I'm going to do some reading, though, and look into implementing it.

[z3p]

Does this key have a passphrase I can use? Alternatively, can you generate one which isn't encrypted?

[z3p]

Nevermind, I'm an idiot. It's in the command you generated it with.

[z3p]

(In [34703]) Branching to 'ecdsa-keys-5350-1'

[Pascal Bouchareine]

Hello, given the age of this report, would it be possible to catch this Exception in twisted.conch.ssh.userauth so that we refuse the key ?

This would prevent an unsupported key proposal to break the negociation process and proceed further to password auth, waiting for a better fix. Thanks!

[Jean-Paul Calderone]

Hello, given the age of this report, would it be possible to catch this Exception in twisted.conch.ssh.userauth so that we refuse the key ? This would prevent an unsupported key proposal to break the negociation process and proceed further to password auth, waiting for a better fix. Thanks!

Already done, I think: #5616. If you still have this problem with Twisted 12.1 or newer, please file a ticket explaining what's up. Thanks!

[Adi Roiban]

So this should be fixed by #5616

Also as of #8828, ECDSA key can not be read/loaded.

Please reopen if you still have problems.