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Simple Cryptology

Handy definitions borrowed without permission from sci.crypt Frequently Asked Questions file:

Cryptology – the study of codes and ciphers

Cryptography – the act of inventing code or cipher systems

Cryptanalysis – the breaking of a code or cipher system without benefit of the normal deciphering mechanism(s)

What is Cryptography? (The Short Version)

“Cryptography is the art and science of hiding data in plain sight. It is also the art and science of stealing data hidden in plain sight.”

(Both accurate definitions, by Larry Loen.)

Have you ever made secret codes with your friends when you were little? Whether it was a number code where each letter of the alphabet had a substituted number, or you made a chart for each of you to translate a message, you were practicing a simple form of Cryptography. As far as I can back up, cryptology wasn’t widely used until World War I, when actual machines were created for the sole purpose of making messages unreadable to the enemy.

Cryptography is the method by which “plaintext” is encrypted into an unreadable form. The plaintext is the original text, before ltering to make it unreadable to other people. The key, or code, is the actual password (or whatnot) used to make it unreadable. This is a very simplistic, and not completely accurate view for which I apologize and again urge anyone seriously interested to read actual hard-copy books and papers for a more detailed explanation.

Why are encrypted communications important?

In today’s electronic communication forums, encryption can be very mportant! Do you know for a fact that when you send a message to someone else, that someone hasn’t read it along the way? Have you ever really sent something you didn’t want anyone reading except the person you sent it to? As more and more things become online, and “paperless” communication predictions start coming true, it’s all the more reason for encryption. Unlike the normal U.S. Mail where it is a crime to tamper with your mail, email-reading can commonly go unnoticed on electronic pathways as your message hops from system to system on its route towards its final destination. Just think, the average Internet letter makes at least two hops before it reaches its recipient, usually more. Even on public BBS’s, your mail is usually stored in plaintext. Can you be sure someone else isn’t reading it? The sysop? Half a dozen co-sysops and hangers-on? How hard would it be for system administrators to set up a process to “grep” (search for known text) all incoming/outgoing mail batches for certain catch phrases? It’s not very hard, I assure you. Although most people probably don’t do things like this, the threat is real. That’s why you need to encrypt your messages. You have the right of privacy, as stated in the Constitution. That’s why cryptography is so key.
Different types of encryption schemes

One-Way encryption algorithms: What are they?

There are certain mathematical/cryptographical algorithms that will encrypt a string of text/numbers using a complex equation. However, you cannot reverse these equations again (take my word for it, it has to do with pieces of the equation being unknown, and purposely lost in the encryption process).

A real-life example of one-way encryption:

These types of algorithms are used when someone needs to compare text, such as in password validation checks. Crypt(), the Unix password validation routine works like this. A password is used at the key to encrypt a plaintext string of 0’s. Then, to verify the password, the computer tries to encrypt the same string of plaintext with the password typed in. If a match is made to the original encrypted text, then the password is valid. (Note: Although you can’t reverse this to find out what the original password/key was, you can compare two encryptions to see if it’s the same key.)

The “One-Time Pad”

A long string of random numbers are generated/created. Messages cannot be any longer than the string of random numbers, but can be shorter.

The text is encrypted by XOR’ing the bits in relation to the random string of numbers. Bit by bit. So, anyone not knowing the original key wouldn’t know whether the string, “123” was really “456” or “789” because in fact the originator and the intended receiver know it’s really, “012” (wrap around 9->0). This is the best explanation I can come up with for this. It’s a proven technique and is considered quite secure.

Single-Key Encryption

This is what most non-crypto-speak people would understand as an encryption system. You enter one string of characters (or whatnot – The KEY) and encrypt your plaintext with this key. Anyone with knowledge of what this key is can decrypt and read the plaintext.

Public-Key Encryption

This is gaining a large following during the time of this writing with such programs as RIPEM, PGP, and the availability of RSAREF, a RSA Public Key algorithm library. RIPEM, and PGP (Pretty Good Privacy by Phil Zimmerman) are both examples of RSA Public Key systems. There are two distinct parts to a public key system, the PUBLIC key and the PRIVATE key.

  • The PUBLIC key is given out to everyone you know who would want to send you an encrypted message.
  • The PRIVATE key you keep secret and do not disclose to anyone.
How it works:

User A (Iskra) wants to send a message to User B (B00gerHed) so Iskra encrypts a message to B00gerHed using BH’s public key that was given out at the last HoHoCon. No one except B00gerHed has the private key to decrypt the message. So he takes his private key, the counterpart to his public key, and decrypts the message sent to him by Iskra. Viola. He now sees that the new red boxes are no longer working because AT&T has cinched up the timing checks. However, Veggie (User C) has intercepted the encrypted message and is trying to figure out what they are talking about. But because he doesn’t have B00gerHed’s private key, he cannot read it. A successful use of public key encryption.

There are a LOT of books on this, so that’s all I’m going to say.

Books, journals et al…

NOTE: A lot of the best and most complete sources of cryptography and some algorithms are classified by the United States Government. However, there are still a decent number I can suggest. Also, the NSA has been pushing for legislation to require all encryption schemes to be “breakable” in a reasonable matter of time with back doors or weaknesses so THEY can decrypt your messages. This is a violation of your rights. I hope you would oppose such things.

David Kahn, The Codebreakers, Macmillan, 1967 [history; excellent]

H.F. Gaines, Cryptanalysis, Dover, 1956 [originally 1939, as Elementary Cryptanalysis].

Abraham Sinkov, Elementary Cryptanalysis, Math. Assoc. of Amer., 1966.

D. Denning, Cryptography and Data Security, Addison-Wesley, 1983.

[Dorothy Denning, also wrote a paper proposing all public key systems be required to register” their private keys with the NSA or other agency for decryption should the gov’t feel it necessary.]

Alan G. Konheim, Cryptography: A Primer, Wiley-Interscience, 1981.

Meyer and Matyas, Cryptography: A New Dimension in Computer Data Security, John Wiley & Sons, 1982.

Books can be ordered from Aegan Park Press. They aren’t cheap, but they are the only known public source for most of these and other books of historical and analytical interest.

Write for catalog to:

Aegean Park Press
P.O. Box 2837
Laguna Hills, CA 92654-0837

Cryptologia: a cryptology journal, quarterly since Jan 1977.
Cryptologia; Rose-Hulman Institute of Technology; Terre Haute, Indiana 47803 [general: systems, analysis, history, …]

Gordon Welchman, The Hut Six Story, McGraw-Hill, 1982. [excellent description of his WW-II crypto work (breaking the German Enigma); discussion of modern cryptological implications]

Various books available from Artech House, 610 Washington St., Dedham, MA 02026; including:

Deavours & Hruh, Machine Cryptography and Modern Cryptanalysis.[operation and breaking of cipher machines through about 1955]

Deavours, et al., CRYPTOLOGY Yesterday, Today, and Tomorrow.[Cryptologia reprints – 1st volume]

Deavours, et al., CRYPTOLOGY: Machines, History & Methods. [Cryptologia reprints – 2nd volume]

Rose-Hulman Institute of Technology
Terre Haute, Indiana 47803
Cryptologia: a cryptology journal, quarterly since Jan 1977.

Journal of the International Association for Cryptologic Research. [quarterly since 1988]

The RSA paper: The Comm. of the ACM, Feb 1978, p. 120.

Claude Shannon’s 2 1940’s papers in the Bell System Tech Journal.

Herbert O. Yardley, The American Black Chamber, Bobbs-Merrill, 1931.
[First hand history – WW-I era]

Edwin Layton, “And I Was There”, William Morrow & Co., 1985.
[First hand history – WW-II]

W. Kozaczuk, Enigma, University Publications of America, 1984.
[First hand history (Rejewski’s) – pre-WW-II]

Journal of Cryptology
Springer-Verlag New York, Inc.
Service Center Secaucus
44 Hartz Way
Secaucus, NJ 07094
$87/year + $8 postage & handling. Published three times a year.

Cryptosystems Journal
Tony Patti, Editor and Publisher
P.O. Box 188
Newtown, PA 18940-0188

$45/year. Published three times a year. Journal dedicated to the implementation of cryptographic systems on IBM PC’s. Emphasis on tutorial/pragmatic aspects. Evidently all articles are written by the publisher.

Forbidden Knowledge
P.O. Box 770813
Lakewood, OH 44107

$18 a year – make check or m/o to Darren Smith (editor). Jack Jeffries (cj137@cleveland.Freenet.Edu) says that this is a local publication which has articles on cryptology. That’s all I know about it.

The Cryptogram
Journal of the American Cryptogram Association
P.O. Box 6454
Silver Spring, MD 20906

This is the Journal of the American Cryptogram Assocation, available by joining the ACA. Dues are probably about $20/year by now. Published six times a year. Contains mostly puzzles for you to solve. No techniques invented after 1920 are used, with simple substitution being the most common. Also contains articles on classical cryptosystems, and book reviews.

The Cryptogram Computer Supplement
Dan Veeneman
P.O. Box 7
Burlington, IL 60109 USA

$2.50/issue. Published three times a year for ACA members. Newsletter for computer hobbyist members of the ACA.

The Public Key
George H. Foot, Editor
Waterfall, Uvedale Road
Oxted, Surry RH8 0EW
United Kingdom

Cost unknown. Magazine devoted to public key cryptography, especially
amongst personal computer owners. Note that RSA’s patents do not apply in
Europe, hence the existence of this magazine.

Lock Box Mail Unit 18757
Washington, DC 20036-8757

6 issues/year, $48.00. Announces new acquisitions and has some news from the intelligence field. Each issue comes with a check-off order form for books announced in that issue.

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