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I am trying to get the MS-MPPE-Send-key and MS-MPPE-Recv-key from the MS-CHAPv2 challenge material. I am able to follow the RFCs 2548 3078 and 3079 to the step of getting the GetNewKeyFromSHA() it is 16 bytes long.

I can use the key to encrypt data as the example in 3079. The problem is that I am not sure what should I do to get the session keys used in the RFC 2548 to get MS-MPPE-Send-key and MS-MPPE-Recv-key fields from there.

I have an example of freeradius and the session key is converted from 16 bytes long to 32 bytes long before the construction of the string stated in RFC 2548.

I have tried to encrypt with RC4 the session keys after GetNewKeyFromSHA() but it is not working for me. If someone could explain a bit in detail this intermediate step it would be nice!

Edit 1

I also have tried to make the encryption in 2548 twice but still no results, I am now digging into the freeRADIUS source code but it is not easy to follow after getting the master key from the MS-CHAPv2 material. Any ideas?

Edit 2

Looking into freeradius it seems to be that firstly it derives the keys from the MS-CHAv2 material but then instead of encrypt an send them, it uses the master secret and the random numbers from the TLS handshake to produce the 32 bytes Send and Receive keys. This is as RFC 2716 says, then encrypts them as RFC 2548 and finally it sends them.

So is it possible to use the master key derived from the MS-CHAPv2 material as in the RFC 3079? or the only way to do this is as freeradius does?

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You're throwing around a lot of RFCs. Can you give a step by step of how you think the derivation should go, and how you see it being performed by freeradius? Also, can you be specific about which sections in the RFCs you're referencing? –  raz Jul 6 at 18:13

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