[strongSwan] Authentication against Linux Users

Christian Salway christian.salway at naimuri.com
Mon May 14 13:52:37 CEST 2018

thanks.  I've swapped over to using NTLM hashes 


Christian Salway 
IT Consultant
Tel: 07463 331432
christian.salway at naimuri.com


> On 14 May 2018, at 10:13, Tobias Brunner <tobias at strongswan.org> wrote:
> Hi Christian,
>> but what if the server stored the password in a sha256(md4(password))
>> hash and then when it received the md4 hash from the client, hashed that
>> with sha256 to compare to?
> It doesn't receive the MD4 hash, which is only a part of the calculation
> of EAP-MSCHAPv2 (the NT password hash).  The actual value that's
> transmitted (ChallengeResponse) and has to be verified (by doing the
> same calculation) also incorporates random challenges (see RFC 2759 [1]
> for details).  Which is why the only thing you can store instead of the
> plainttext password is the NT hash (ntlm secrets in swanctl.conf).
>> The Server can send any fake md4 hash across the network to the client
>> (unless the client does its own check of the hash)...
> It does, the server sends its an AuthenticatorResponse, which
> incorporates the client's response and the random challenges (including
> one provided by the client) to prove it knows the password.  So the EAP
> method does provide mutual authentication, however, a weak version
> because the server is authenticated after the client.  Which means a
> MITM could attack a weak client password, which is why the server should
> be authenticated via IKEv2 pubkey authentication first (i.e. EAP-only
> authentication is not allowed for EAP-MSCHAPv2).  EAP-MSCHAPv2 can also
> be tunneled in another EAP method (e.g. EAP-TTLS or EAP-PEAP) to
> authenticate the AAA server first.
> There are, of course, several other EAP methods based on passwords, with
> much stronger algorithms and some of them don't require plaintext
> passwords.  The problem is that common clients (as those built-in
> Windows and Apple OSes) don't support them (and neither does strongSwan
> actually).
> Regards,
> Tobias

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