Re: Pretty Good Piracy

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On 10/5/97 6:37 PM, Anonymous (nobody@REPLAY.COM)  passed this wisdom:

>Ryan Anderson wrote:
>> Okay - the only difference between this and a normal version of 
>> PGP is that it always encrypts to a certain key-id, in addition
>> to all others.
>> 
>> That's the only weakness you'll see in it.
>
>It's the only weakness that's needed to compromise all the keys.

 It seems to me that it should not necessarily compromise all keys,
though it does in effect provide for a goodly number of 'known
plaintext' objects. Could some of our hardcore crypto experts comment
on IDEA's susceptability to known plaintext which then provides
'plaintext' to the DH/DSS or RSA keys and what is their susceptability
to 'known plaintext'

 It occured to me while proofreading the above that in effect a
digitally signed cleartext document provides 'known plaintext' every
time its used, since the SHA-1/MD-5 can be computed the hash is a
'known plaintext' on the  DH/DSS and RSA keys ... is this one of the
reasons for the two key types in PGP5 ???


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Brian B. Riley --> http://www.macconnect.com/~brianbr
  For PGP Keys  <mailto:brianbr@together.net?subject=Get%20PGP%20Key>

  "Never ask what sort of computer a guy drives. If he's a Mac user,
   he'll tell you. If not, why embarrass him?" - Tom Clancy

On Sun, 5 Oct 97 19:51:06 -0400
"Brian B. Riley" <brianbr@together.net> wrote
regarding "Re: Pretty Good Piracy":

<snip>
: It occured to me while proofreading the above that in effect a
:digitally signed cleartext document provides 'known plaintext' every
:time its used, since the SHA-1/MD-5 can be computed the hash is a
:'known plaintext' on the  DH/DSS and RSA keys ... is this one of the
:reasons for the two key types in PGP5 ???
<snip>
The reason for having two key types for PGP5 is that DH is only capable
of key distribution, not signing.  and DSS is only capable of signing. 
Hence, you require one key to sign, and one to distribute the session
key.

;____________________________________________________________________
;                  
;                                      aldius@mindless.com
;____________________________________________________________________
;

Aldius <aldius@mindless.com> writes:
> The reason for having two key types for PGP5 is that DH is only capable
> of key distribution, not signing.  

DH is an interactive key negotiation protocol.

El Gamal is the key exchange algorithm used in PGP5.  For some reason
PGP Inc insists on calling El Gamal "DH".  El Gamal is a variant of
DH; so it is related.  But El Gamal is not DH, and it is bad
terminology to call it DH.

The only reason I can think that they insist on calling El Gamal "DH"
at every opportunity is that they perhaps think that the name DH
(Diffie-Hellman) is more widely known, and want to give people warm
fuzzies "oh I've heard of that algorithm".

> and DSS is only capable of signing.  Hence, you require one key to
> sign, and one to distribute the session key.

right.

Adam
-- 
Now officially an EAR violation...
Have *you* exported RSA today? --> http://www.dcs.ex.ac.uk/~aba/rsa/

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