Subject: Mixing rsa and dh/dsa

From: "James H. Cloos Jr." <[email-masked]>
Date: 13 Apr 1999 14:31:12 -0500

Given a recipient with only an RSA keypair (algo 1), and a sender with
only a DSA/Elgamal pair (algos 17 and 16), should the sender
encrypt+sign, will any extant software be able to decrypt and verify?

- -JimC
- -- 
James H. Cloos, Jr.  <http://www.jhcloos.com/cloos/public_key> 1024D/ED7DAEA6 
<[email-masked]>     E9E9 F828 61A4 6EA9 0F2B  63E7 997A 9F17 ED7D AEA6

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From: Tom Zerucha <[email-masked]>
Date: Tue, 13 Apr 1999 17:41:03 -0400

> encrypt+sign, will any extant software be able to decrypt and verify?

Yes.  The encryption is done using the RSA algorithm, but the signing is
done using DSA.  The recipient can decrypt using his RSA key and verify
from the DSA from a keyserver or keyring.

The encryption algorithm is separate and thus can be different from any
signature algorithm.

My test suite generates every possible combination, so I know it is
possible for this to work.  Whether any particular implementation handles
this depends on that implmementaiton, but there should not be any problems
if they simply did things in an obvious manner.

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From: Jon Callas <[email-masked]>
Date: Wed, 21 Apr 1999 15:05:31 -0700

At 02:31 PM 4/13/99 -0500, James H. Cloos Jr. wrote:

|Given a recipient with only an RSA keypair (algo 1), and a sender with
|only a DSA/Elgamal pair (algos 17 and 16), should the sender
|encrypt+sign, will any extant software be able to decrypt and verify?
|

If the sender has software that can do RSA, yes. If their software can't do
RSA (for example, suppose they had an NAI/PGP freeware version), then the
sender cannot encrypt to the recipient.

Any OpenPGP-compliant version, though will be able to verify DSA sigs and
encrypt to Elgamal keys.

Does that answer your question? Really your question is an implementation
question, not a standards question.

	Jon

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Jon Callas                                  [email-masked]
CTO, Total Network Security                 3965 Freedom Circle
Network Associates, Inc.                    Santa Clara, CA 95054
(408) 346-5860                              
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