Cryptography

1. Cryptography Gerard Klonarides

2. What is cryptography? • Symmetric Encryption • Asymmetric Encryption • Other cryptography • Digital signatures • PKI

3. What is Cryptography? • Transforming plaintext to ciphertext Hello I love you won’t you tell me your name? Hello I love you won’t you tell me your name?

4. Cryptography • Transforming plaintext into ciphertext • Substitution • Transposition

5. Substitution • 123453452345231 • This = 1234 • Try and crack this one

6. This is his hit • 123453452345231

7. Transposition • Plaintext elements rearranged • This is his hit • ihT sis sih tih

8. Plaintext is processed • Block cipher • A block at a time • Stream cipher • Processed continuously

9. The Cipher Process • Keys • Single Key • Two-key encryption

10. About Keys • Bigger does not mean better • For example IDEA 128 is better than RSA 521 • One has to protect the integrity of the keys

11. What does 128 bit encryption mean? • A 128-bit number has 2128 possible values. • How big is that? • 218 is how many IPv6 addresses we have • 2170 is the # of atoms in the earth • 2190 is the # of atoms in the sun

12. Encryption types • Single key Encryption • Conventional • Symmetric • Two-key Encryption • Asymmetric • Public-key

13. Symmetric Encryption A type of encryption where the same key is used to encrypt and decrypt the message. This differs from asymmetric (or public-key) encryption, which uses one key to encrypt a message and another to decrypt the message.

14. Asymmetric Encryption • cryptographic system that uses two keys -- a public key known to everyone and a private or secret key known only to the recipient of the message. When John wants to send a secure message to Jane, he uses Jane's public key to encrypt the message. Jane then uses her private key to decrypt it. • An important element to the public key system is that the public and private keys are related in such a way that only the public key can be used to encrypt messages and only the corresponding private key can be used to decrypt them. Moreover, it is virtually impossible to deduce the private key if you know the public key. • Public-key systems, such as Pretty Good Privacy (PGP), are becoming popular for transmitting information via the Internet. They are extremely secure and relatively simple to use. The only difficulty with public-key systems is that you need to know the recipient's public key to encrypt a message for him or her. What's needed, therefore, is a global registry of public keys, which is one of the promises of the new LDAP technology. • Public key cryptography was invented in 1976 by Whitfield Diffie and Martin Hellman. For this reason, it is sometime called Diffie-Hellman encryption. It is also called asymmetric encryption because it uses two keys instead of one key (symmetric encryption).

15. Algorithms A formula or set of steps for solving a particular problem. To be an algorithm, a set of rules must be unambiguous and have a clear stopping point. Algorithms can be expressed in any language, from natural languages like English or French to programming languages like FORTRAN. • We use algorithms every day. For example, a recipe for baking a cake is an algorithm. Most programs, with the exception of some artificial intelligenceapplications, consist of algorithms. Inventing elegant algorithms -- algorithms that are simple and require the fewest steps possible -- is one of the principal challenges in programming.

16. The RSA Algorithm • Developed by Ron Rivest, Adi Shamir, and Len Adlerman from MIT in 1977 • The only widely accepted public-key algorithm • A block cipher algorithm • 98%

17. Authentication • The ability to verify that the contents of a message have not been altered • The ability to identify the owner of that message

18. The Authentication Process • To create an authenticator • To check for authenticity

19. Hash Algorithms • MD5 -Message Digest Algorithm • SHA - Secure Hash Algorithm • DSS – Digital Signature Standard

20. DSS FIPS 186-2 • SUMMARY: The Secretary of Commerce approved Federal Information Processing Standard (FIPS) 186-2, Digital Signature Standard (DSS), which supersedes Federal Information Processing Standard (FIPS) 186-1, Digital Signature Standard (DSS). FIPS 186-2 expands FIPS 186-1 by specifying an additional voluntary industry standard for generating and verifying digital signatures. This action will enable Federal agencies to use the Digital Signature Algorithm (DSA), which was originally the single approved technique for digital signatures, as well as two new ANSI Standards that were developed for the financial community. These new standards are ANSI X9.31, Digital Signature Using Reversible Public Key Cryptography, and ANSI X9.62, Elliptic Curve Digital Signature Algorithm (ECDSA). • EFFECTIVE DATE: This standard is effective June 27, 2000.

21. Diffie-Hellman key agreement • The Diffie-Hellman key agreement protocol (also called exponential key agreement) was developed by Diffie and Hellman [DH76] in 1976 and published in the ground-breaking paper ``New Directions in Cryptography.'' The protocol allows two users to exchange a secret key over an insecure medium without any prior secrets.