From msuinfo!agate!howland.reston.ans.net!cs.utexas.edu!cactus.org!ritter Wed Mar 2 09:52:20 1994 Newsgroups: sci.crypt Path: msuinfo!agate!howland.reston.ans.net!cs.utexas.edu!cactus.org!ritter From: ritter@cactus.org (Terry Ritter) Subject: Penknife Email Cipher Available Message-ID: <1994Feb28.063510.9665@cactus.org> Organization: Capital Area Central Texas UNIX Society, Austin, Tx Distribution: usa Date: Mon, 28 Feb 1994 06:35:10 GMT Lines: 114 INTRODUCING THE PENKNIFE EMAIL CIPHER from Ritter Software Engineering For a limited time, the commercial demo version of the Penknife cipher for DOS is available free by email to US citizens within the US only. (The Unix program uudecode--or equivalent--must be used to recover the DOS executable binary). Each email request must include: 1) Correct name, address, and phone, 2) Email address, city and state of email server, 3) Statement of US citizenship, and 4) Agreement to not export the program. Description Penknife is a commercial command-line file-cipher program for 80x86 DOS, which can encipher any file of any type into email-able text (ciphertext) lines. The commercial demo contains the same cipher used in the advanced version, but without various frills like key-aliases and wildcard processing. The demo may be further distributed (within the US only) to other email users. Individuals may evaluate the demo version until they decide to upgrade to advanced Penknife. Penknife uses a 63-bit internal key, so it cannot be exported and should not be placed on a BBS or ftp site. Secret-Key Cipher Penknife is a secret-key cipher; the need for a secret key reminds us that privacy is not available if the other end cannot be trusted. Admittedly, key-transport is sometimes awkward (even though enciphered keys can sent by mail or express-delivery service, taken by traveling friends or employees, or delivered in person). But the alternative is sometimes worse: Public-key algorithms absolutely *require* a cryptographic protocol so a user can "validate" or "certify" each public key they acquire. Failure to validate keys can result in "man-in-the-middle" or "spoofing" attacks which expose the protected information *without* any need to break the cipher. This makes detailed discussion of the "strength" of such a cipher irrelevant to its true security. The need to manually validate keys is a weakness which only crypto- trained operators would recognize and cover, a weakness which Penknife does not have. Good public-key ciphers exist, but these do not "trust" other users, instead using a cryptographic protocol to certify keys. This is a complication which Penknife does not need. Some Penknife Features 1) Penknife is based on original Dynamic Substitution technology invented and patented by this author and published in Cryptologia. The detailed cipher design is available and has been published for comment on sci.crypt. 2) Penknife is error-resilient: Each ciphertext line is ciphered separately, and the cipher recovers from errors with the start of each new ciphertext line. Each ciphertext line has its own 32-bit random line key. 3) Penknife deciphering automatically handles both DOS-style (CR LF) and Unix-style (LF) text lines, since text line- separators may change in transit. 4) Penknife does not include "BEGIN ENCIPHERED MESSAGE" or any other indication of cipher, or the name of the cipher used. There is just ciphertext. The receiving user is expected to know that a cipher has been used, and which cipher in particular, as well as the key. 5) In most cases, Penknife deciphering will automatically skip email headers or signature text (or optionally pass them through to the output file). It is normally unnecessary to "clean up" email messages for deciphering. 6) Penknife includes an overall error-check (32-bit CRC) on the ciphered data. This supports the transport of programs, which should not be executed if they were damaged. It also indicates the use of the wrong key when deciphering. 7) The Penknife advanced version has extensive key-management support, including enciphered alias files. Key-aliases reduce the irritation and potential for serious error which can result from typing-in long secret keys. 8) Advanced Penknife also includes dated aliases, which support automatic key-change by date, as well as access to archived ciphertext enciphered under old keys. 9) Advanced Penknife also supports ciphertext archives, wildcard and directory-tree search operations, automatic recovery of alias and date from the filename (supporting automatic deciphering of archived ciphertext from various old keys) as well as a simple batch facility. 10) Penknife does not infringe any known patents. Ritter Software Engineering is a registered manufacturer of cryptographic armaments. --- Terry Ritter ritter@cactus.org