An Overview of Cryptography

[Nytro]

An Overview of Cryptography

Gary C. Kessler

21 April 2011

CONTENTS

    1. INTRODUCTION
    2. THE PURPOSE OF CRYPTOGRAPHY
    3. TYPES OF CRYPTOGRAPHIC ALGORITHMS
        3.1. Secret Key Cryptography
        3.2. Public-Key Cryptography
        3.3. Hash Functions
        3.4. Why Three Encryption Techniques?
        3.5. The Significance of Key Length 4. TRUST MODELS
        4.1. PGP Web of Trust
        4.2. Kerberos
        4.3. Public Key Certificates and Certification Authorities
        4.4. Summary
    5. CRYPTOGRAPHIC ALGORITHMS IN ACTION
        5.1. Password Protection
        5.2. Some of the Finer Details of Diffie-Hellman Key Exchange
        5.3. Some of the Finer Details of RSA Public-Key Cryptography
        5.4. Some of the Finer Details of DES, Breaking DES, and DES Variants
        5.5. Pretty Good Privacy (PGP)
        5.6. IP Security (IPsec) Protocol
        5.7. The SSL "Family" of Secure Transaction Protocols for the World Wide Web
        5.8. Elliptic Curve Cryptography
        5.9. The Advanced Encryption Standard and Rijndael
        5.10. Cisco's Stream Cipher
        5.11. TrueCrypt
    6. CONCLUSION... OF SORTS
    7. REFERENCES AND FURTHER READING
    A. SOME MATH NOTES
        A.1. The Exclusive-OR (XOR) Function
        A.2. The modulo Function
    ABOUT THE AUTHOR

1. INTRODUCTION

Does increased security provide comfort to paranoid people? Or does security provide some very basic protections that we are naive to believe that we don't need? During this time when the Internet provides essential communication between tens of millions of people and is being increasingly used as a tool for commerce, security becomes a tremendously important issue to deal with.

There are many aspects to security and many applications, ranging from secure commerce and payments to private communications and protecting passwords. One essential aspect for secure communications is that of cryptography, which is the focus of this chapter. But it is important to note that while cryptography is necessary for secure communications, it is not by itself sufficient. The reader is advised, then, that the topics covered in this chapter only describe the first of many steps necessary for better security in any number of situations.

This paper has two major purposes. The first is to define some of the terms and concepts behind basic cryptographic methods, and to offer a way to compare the myriad cryptographic schemes in use today. The second is to provide some real examples of cryptography in use today.

I would like to say at the outset that this paper is very focused on terms, concepts, and schemes in current use and is not a treatise of the whole field. No mention is made here about pre-computerized crypto schemes, the difference between a substitution and transposition cipher, cryptanalysis, or other history. Interested readers should check out some of the books in the bibliography below for this detailed — and interesting! — background information.

Tutorial:

http://www.garykessler.net/library/crypto.html

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