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List:       ms-cryptoapi
Subject:    Re: Diffie Hellman shared secret accessiblity
From:       Jeff Spelman <jeffspel () MICROSOFT ! COM>
Date:       1999-03-26 16:29:31
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Shilpa
   Currently released versions of the Microsoft DSS/DH CSP do not allow
direct access to the DH agreed secret.  This is due to US export
restrictions.  In addition the key derivation you describe below is also not
currently supported.
Thanks Jeff

-----Original Message-----
From: S Bansod [mailto:sbansod@FCPL.CO.IN]
Sent: Thursday, March 25, 1999 9:30 PM
To: CryptoAPI@DISCUSS.MICROSOFT.COM
Subject: Diffie Hellman shared secret accessiblity


Hello,
I had requested information about accessing the Diffie - Hellman shared
secret (the pre-master key) generated  using MS DH/DSS CSP,somewhere in
08/98 and had learnt that such functionality was not supported by the MS DH
CSP. I have been busy with something else, and checked the archives hoping
to find some development on this front, but in vain. I have gone through a
few crypto libraries. However, I would like to know if MS is planning to
provide such support (of making the shared secret accessible or implementing
functionality some of us need)in days to come. I am very eager to continue
using MS CAPI for my work but cannot do so due to this one problem.
Either one of the following functionalities provided would solve my problem
1)Access to the value of shared secret
2)Once the DH key of peer host has been obtained using CryptImportKey(),
the shared secret generated would be say 'K'.
The encryption and integrity keys sould be generated as
EncryptKey_Client_to_Server =
HASH(K||"C"||session_id)EncryptKey_Server_to_Client =
HASH(K||"D"||session_id)Integrity_Client_to_Server =
HASH(K||"E"||session_id)
Integrity_Server_to_Client = HASH(K||"F"||session_id)
where session_id is a byte stream

Please let me of some information in this direction.
Thanks
Shilpa

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