[cifs-protocol] [Pfif] MS-NRPC: AES Schannel problems
Stefan (metze) Metzmacher
metze at samba.org
Sat Aug 29 00:27:49 MDT 2009
> A quick clarification for the AES bit in Negotiate Flag, as shown in 22.214.171.124. The information in the document regarding this bit is wrong. Bit W NETLOGON_NEG_SUPPORTS_AES_SHA2 (0x00400000) is not supported in Windows 7/Windows Server 2008 R2. The right bit to negotiate AES support should be NETLOGON_NEG_SUPPORTS_AES(0x01000000), as you already indicated. If you use bit 0x00400000 to negotiate the AES support, it might be the source of your problem.
I was already only using the correct bit.
> I will file a request to fix this problem in the document. Meanwhile, I will work on the AES encryption details for Schannel.
> -----Original Message-----
> From: Stefan (metze) Metzmacher [mailto:metze at samba.org]
> Sent: Friday, August 28, 2009 12:00 PM
> To: Hongwei Sun
> Cc: pfif at tridgell.net; cifs-protocol at samba.org
> Subject: Re: [Pfif] MS-NRPC: AES Schannel problems
> Stefan (metze) Metzmacher schrieb:
>>> The SharedSecret used for AES session key computation, as described in 126.96.36.199 MS-NRPC , should be the NTOWF (MD4(UNICODE(Passwd))) of the plaintext password. The section 3.1.1 of MS-NRPC explains what a SharedSecret is used for session key calculation in Windows implementations. The SharedSecret is stored in UnicodePwd AD attribute. Please see section 3.1.1 and Windows Behavior notes <66>,<67> of MS-NRPC for details.
>> Yes, I saw that and that's why I've also done it like this, but I was
>> wondering why Section 3.4.1 has M4SS := MD4(UNICODE(SharedSecret))
>> explicit for the hmac_md5 session key and the des session key.
>> I think it would make sense to also add it to the hmac_sha256 section
>> in order to remove the confusion I had.
>>> I will continue working on all questions related to AES encryption.
>> Thanks, as it seems I compute the session key correct, this is the
>> (netlogon_creds_step_crypt()) where I have a bug, because I'm getting
>> access denied when I try DCERPC_SCHANNEL_AES against a w2k8r2rc server.
> Please also provide details about the aes encryption used when schannel acts as security provider for dcerpc.
> I noticed that the documentation on has only the
> NETLOGON_NEG_SUPPORTS_AES_SHA2 (0x00400000) flag, but w2k8r2 used the new flag NETLOGON_NEG_SUPPORTS_AES(0x01000000).
> I assume the docs may missing also some crypto details, because of this...
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