Crypto questions

[Joseph Ashwood]

Honestly, it's pretty easy to take care of everything you need. Since you're
using SMTP you obviously know how long the message is so you can use fairly
well anything. Also because it's going over SMTP you need to be aware that
you should base-64 encode everything, and the other issues. However what you
need is simply:
a random number generator
an implementation of RSA-OAEP
a good block cipher with a good chaining method (Rijndael, CBC is great)
a signature scheme

do the following
generate a 128-bit number K
D = RSA-OAEP(K)
B = data | signature(data)
S = D | RijndaelCBC(K, B)
send(base-64(S))

Toss in some markers, something along the lines of "---Begin PGP encrypted
message---" and it should work wonderfully. The reverse should be obvious,
but just to make sure
T = receive()
S = base-64Decode(T)
(D, B)= Parse(S)BasedOnMarking
K = RSA-OAEPDecrypt(D)
data = RijndaelCBCDecrypt(K, B)

You can send anything you want this way. You can also add compression to the
data before encryption, and decompress after decryption. It's not bleeding
edge, but it's dependable, it's fast, it's secure, and if you're really
paranoid about security, move to SHA-256 with RSA-OAEP, and use a 256-bit
Rijndael key. You'll also need to make sure you use properly sized RSA keys.

If you want something closer to bleeding edge, go with XTR in place of RSA,
and well Rijndael is just an all around great cipher. If you want to strive
for exotic, use XTR and Serpent. Of course if you want the tried and true
use 3DES instead of Rijndael. If you want the most buzzwords for you
condition use half-ephemeral ECC like this:
do the following
generate a random private key
generate the public key to go with it, P
Compute the shared secret, K
B = data | signature(data)
S = P | RijndaelCBC(K, B)
send(base-64(S))
Decryption is left as an exercise. If you'd like more help there are plenty
of people on the cypherpunks list (myself included) that are capable of
consulting to determine what parameters you need to use.
                        Joe

----- Original Message -----
From: "Scoville, Chad" <CScoville at thrupoint.net>
To: <cypherpunks at toad.com>
Cc: <tech777_2000 at yahoo.com>
Sent: Tuesday, December 19, 2000 9:35 AM
Subject: Crypto questions


> I've been actively reading posts on this list for about two years now, and
> I'm in he process of actually trying to design/implement a data network
> where security is of the utmost priority. Where is a good starting point
to
> find out about packages using algorithms which are unbreakable as of yet.
> All of the traffic will remain domestically within the US. The traffic
will
> be SMTP.
>
> It would be illmatic if someone could reccomend a good reading list
> (current) on the bleeding edge of cryptography.
>
> Tks. in advance.
>
> CK$
>
> Chad K. Scoville
> Internetwork Solutions Engineer
> Thrupoint, Inc. formerly Total Network Solutions
> 545 Fifth Avenue, 14th Floor
> New York, NY
> 10017
> v 212.542.5451
> p 800.555.9172
> cscoville at thrupoint.net
> www.thrupoint.net
>
>