2. HEY DOUG HOW ARE YOU?
NKE JUAM NUC GXK EUA

3. Cryptography
Jason Gruber
COSC 356-1

4. Outline Cryptography Terminology Types of encryption Symmetric Key
Asymmetric Key
Examples of different encryption methods
Questions

5. Cryptography Terms Cryptography
the study of ways to convert information from normal, comprehensible form into an incomprehensible format, rendering it illegible without ‘secret knowledge’
Cipher
Algorithm for performing encryption and decryption
Key
Small amount of information used to encrypt / decrypt information (aka ‘secret knowledge’)
Plain/Clear Text
Information in its normal comprehensible form
Ciphered Text
Information that has been encrypted

6. 2 Types of Encryption… The First Type
Symmetric key ciphers use the same key for encryption and decryption
"private-key", "one-key" and "single-key" cryptography
block ciphers and stream ciphers
Drawback: Key must be shared in a non-traditional communication medium
else the key and encrypted data can be collected & decrypted by anyone

7. Stream Cipher Encrypts bit-per-bit RC4, FISH, and Helix
The algorithm uses some function to combine a pseudorandom number generator (PRNG) with a plaintext stream (resulting in a key stream)
Encryption consists of XORing the plaintext bits with the corresponding bits of the keystream; decryption consists of XORing the ciphertext bits with the corresponding keystream bits

8. Block Cipher Encrypts block-per-block Generally 64 or 128 bits
DES, AES, IDEA

9. 2 Types of Encryption… The Second Type
Asymmetric key ciphers use a public and a private key, for encryption and decryption respectively
Public key algorithms are usually based on hard mathematical problems. RSA, for example, relies on the (conjectured) difficulty of factorisation
Although generally slower than symmetric, Asymmetric keys can be used to verify identity of sender.

10. Asymmetric Key Ciphers
Plain text is encrypted using public key
Corresponding private key is required to decrypt back to plain text
Attempts to decrypt using public-key or any other key than specific private key will result in garbage.
Key ranges from 160 – 510 bits

11. Caesar Cipher Key is a numerical value (1-26)
Key value represents the number of “shifts”
Original
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
G H I J K L M N O P Q R S T U V W X Y Z
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
HEY DOUG HOW ARE YOU? =
NKE JUAM NUC GXK EUA

12. RC4 is the most widely-used software stream cipher
It has become part of some commonly used encryption protocols and standards, including WEP and WPA for wireless cards and SSL
A number of attacks on RC4 have been published, and have demonstrated that some ways of implementing RC4 within a cryptosystem are completely insecure. However, it is believed that RC4 can be secure when used appropriately
RC4 was designed by Ron Rivest of RSA Security in 1987; while it is officially termed "Rivest Cipher 4", the RC acronym is alternatively understood to stand for "Ron's Code"

13. RSA asymmetric algorithm widely used in electronic commerce protocols
The algorithm was described in 1977 by Ron Rivest, Adi Shamir and Len Adleman who were all at MIT at the time
the RSA system relies on the difficulty of factoring very large numbers
As of 2004, there is no known method of attack which is feasible against the basic algorithm, and sufficiently long RSA keys make brute force attacks infeasible -- that is, effectively impossible

14. Data Encryption Standard (DES)
selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976
initially controversial, with classified design elements, a relatively short key length, and suspicions about an NSA backdoor
DES is now considered to be insecure for many applications. This is chiefly due to the 56-bit key size being too small; DES keys have been broken in less than 24 hours
believed to be practically secure in the form of Triple DES
the cipher has been superseded by the Advanced Encryption Standard (AES)

15. Triple DES (3DES)
a block cipher formed from the Data Encryption Standard (DES) cipher
developed by Walter Tuchman (the leader of the DES development team at IBM)
is specified in FIPS Pub 46-3
Triple-DES is defined as performing a DES encryption, then a DES decryption, and then a DES encryption again 3DES=(DES(DES(DES(text))))

16. Advanced Encryption Standard (AES)
also known as Rijndael (a combo of its inventor’s last names (Joan Daemen and Vincent Rijmen) )
block cipher adopted as an encryption standard by the US government, and is expected to be used worldwide and analyzed extensively
adopted by National Institute of Standards and Technology (NIST) as US FIPS PUB 197 in November after a 5-year standardization process
andard

17. Questions??