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Re: Defeating MITM with Eric's Secure Phone
- To: [email protected]
- Subject: Re: Defeating MITM with Eric's Secure Phone
- From: Mix <[email protected]>
- Date: Fri, 10 Oct 1997 14:12:16 -0700 (PDT)
- Comments: This message did not originate from the address above. It was remailed by an anonymous remailing service. If you have questions or complaints, please direct them to <[email protected]>
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Adam Back wrote:
>Monty Cantsin writes:
>> My apologies if this has already been discussed, but wouldn't this be
>> a straightforward solution?
>
>John Kelsey described the same system.
>
>[adding hex passphrase digits exchanged via PGP to display digits]
>
>> Any flaws?
>
>See my other recent post in this thread... I think it doesn't work
>because Mallet can recover the passphrase. You must remember that
>when Mallet is actively doing a MITM attack he knows the digits on
>the display of each party. With that info he can recover the
>passphrase by subtracting. Then he can give Alice the correct
>checksum for the link A<->M and Bob the correct checksum for the link
>M<->B.
Oh, I get it. Thanks.
And now I get why people want to assign passwords to each digit.
Mallory has no way of knowing all the mappings, even when one is
revealed.
Just to get a feel for what this looks like, a table like this one
could be exchanged in advance of each telephone call. (Nothing here
is my invention, of course.) The columns are used once successively
for each digit.
0: Tientsin bedeviling Menominee bonneted coincides quotation
1: handling Bernadine prouder Navaho fittingly Swinburne
2: degrading Puritanizes allophone acquaint jack renditions
3: clientele homo Verderer diskettes overview surmounts
4: delimiting probes sobering modulating situated jelly
5: bewail reflex multistage plastics stigmata scandal
6: Genoa divider synonym bipeds tale denominators
7: aborts carbons welding amalgam chain innovation
8: salvaging Fargo transitional relishes Ozarks meditations
9: overlapping Tehran desperation initiated intimidate beggars
A: whereby muffins Soddy miniatures diagnostic proportionment
B: flour pistils aback despatched Rydberg tales
C: lifespan sallying Arianist kindness side corporal
D: wrongs nervousness minting totaller feather copyrightable
E: intoxicated Yukon Boyd response ingredients numismatist
F: stairway imitation consulted printably anesthetizes interval
This has about 85 bits of entropy assuming the words are randomly
selected from a pool of 20,000. As Mallory only gets one try, those
are very good odds. This is completely practical and secure because
the table is easy to generate and exchange.
(Not that an in-band method wouldn't be way cool!)
Monty Cantsin
Editor in Chief
Smile Magazine
http://www.neoism.org/squares/smile_index.html
http://www.neoism.org/squares/cantsin_10.html
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