1. Crytography
Chapter 8

2. Cryptology Cryptography Cryptanalysis Comes from Greek
Kryptos meaning “hidden”
Grahein meaning “to write”
Process of making and using codes to secure the transmission of information
Cryptanalysis
Process of obtaining the original message form encrypted message

3. Cryptology Encryption Decryption
Process of converting an original message into a form that is unreadable to unauthorized individuals
Decryption
Process of converting the encrypted message (cipertext) into an easily read message (plain text)

4. Basic Definitions Algorithm Cipher Ciphertext or cryptogram Code
Programmatic steps to encrypt message
Cipher
Encryption method or process
Ciphertext or cryptogram
Encrypted message
Code
Process of converting unencrypted components into encrypted components

5. Basic Definitions Decipher Encipher Key or crypto-variable Key-space
Convert to plaintext
Encipher
To encrypt
Key or crypto-variable
Information used with the algorithm to encrypt
Key-space
Entire range of values that can possibly be used to construct an individual key

6. Basic Definitions Link encryption
Series of encryptions /decryptions between a number of systems
Plaintext or clear text
The original message
Steganography
Process of hiding messages
Work factor
Amount - effort required to perform cryptanalysis

7. Cipher methods Bit stream method Block cipher method
Each bit in the plaintext is transformed bit by bit
Most common use XOR
Block cipher method
Messaged divided into blocks
Each block is encoded
Substitution, transposition, XOR or combination

8. Substitution Cipher Substitute one value for another
3 character substitution to the right
Original alphabet: ABCDEFGHIJKLMNOPQRSTUVWXYZ
Encrypted alphabet:
DEFGHIJKLMNOPQRSTUVWXYZABC
Simple by itself – powerful when combined with other operations

9. Substitution Cipher Polyalphabetic substitution
Orig: 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
Sub1: D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
Sub2: 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
Sub3: 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
Sub4: 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
Sub5: 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
Using this technique what is? ZTPG
3 shift to the right is know as the Caesar Cipher

10. Vigenere Cipher Implemented using the Vigenere Square
26 distinct cipher alphabets
Header row – normal order
Each additional row – shift right
Start in first row and find a substitution for one letter
Move down the rows for each subsequent letter of plaintext

12. Transposition Cipher Simply rearranges the values within a block
Can be done at the bit level or the byte level
Key pattern: , , , ,5 7,
7 6,8 3
Julius Caesar was associated with the early version of this cipher also
Larger blocks or keys makes cipher stronger

13. Exclusive OR (XOR) Function of Boolean algebra Two bits are compared
If identical, result is binary 0
If not identical, result is binary 1
Very simple encryption
Not very secure

14. Vernam Cipher One-time pad
Uses a set of characters only one time for each encryption process
Each character of the plaintext is turned into a number and a pad value for that position is added
Sum is then converted back to a cipher text
Decryption requires knowledge of pad values or difficult cryptanalysis.

15. Book or Running Key Cipher
Cipher text
List of codes representing a page number, line number, and word number of the plaintext word.
Must know which book was used

16. Hash functions Not an encryption methodology
Mathematical algorithm -generates a message summary or digest
Fingerprinting
Used to determine if it is the same message
Not used to decypher
Message always provide same hash value if unaltered

17. Hash functions Do not require keys
Uses Message Authentication Code (MAC)
Key-dependent
Used in password verification systems

18. Secure Hash Standard (SHS)
Secure algorithm
Standard issued by National Institute of Standards and Technology (NIST)
SHA-1 Produces a 160 bit digest
Family of SHA
SHA-256
A 256-bit cipher algorithm
Creates a key - encrypting the intermediate hash value with the message block functioning as the key

19. Cryptographic Algorithms
Symmetric and asymmetric and hybrid
Distinguished by the types of keys they use
Symmetric Encryption
Requires the same secret key
Encryption methods use mathematical operations
Both the sender and receiver must have the secret key
Primary challenge – getting key to receiver

20. Symmetric Encryption Cryptosystems
Data Encryption Standard (DES)
Key length of 128 bits
64-bit block size
56-bit key
Too weak
Triple DES (3DES)
Advanced Encryption Standards
Used by federal agencies other than national defense
Declassified, publicly disclosed, royalty-free
Uses block cipher, variable length block, key length of 128, 192, or 256

21. Asymmetric Encryption
Uses two different but related keys
Either key can encrypt or decrypt
Must use other to perform other function
One key private
One key public
Also know as public key encryption
Based on one-way functions
One is simple to compute , the opposite is complex

22. Asymmetric Encryption
Based on hash value
Uses mathematical trapdoor
Secret mechanism that enable you to easily accomplish the reverse function in a one-way function.
Public key becomes the true key
Private is derived form public key using trapdoor

23. Public Key RSA (Rivest-Shamir-Adlemann)
First public key encryption algorithm
Published for commercial use
E-commerce browsers
Has become the de facto standard

24. Encryption Key Size Cryptovariable or key size must be decided
Length of key increase the number of random selections to be guessed
Length of key influences strength
The security of encrypted data is NOT dependent on keeping the algorithm secret
Depends on keeping some or all of the elements of the keys secret
See table on page 367

25. Public Key Infrastructure (PKI)
Integrated system of software, encryption methodologies, protocols, legal agreements, and 3rd part services
Based on public key
Include digital certificates and certificate authorities

26. Digital Certificates
Public key container files that allow computer program to validate the key and identify to whom it belongs.
Allows integration of key characteristics to be integrated into business practices
Authentication
Integrity
Privacy
Authorization
Non-repudiation

27. Digital Certificate Used by third party
Certifies the authenticity of the
Digital signature is attached
Certify that file is from the entity that it claims to be
Has not been modified
Certificate authority
Software agent
Manages the issuance of certificates
Serves as the electronic notary pubic
Verify the certificates worth and integrity

28. PKI Common implementation
Systems to issue digital certificates to users and servers
Directory enrollment
Key issuing systems
Tools for managing the key issuance
Verification and return cetificates

29. Digital Signatures
Created to verify information transferred using electronic systems
Currently asymmetric encryption processes are used to create digital signatures
Encrypted messages that can be mathematically authentic
Used when using DSS (digital Signature Standard)

30. Digital Signatures Process Create a message digest using the hash
Input into the digital signature algorithm along with a random number to be used for generating the digital signature
Depends upon the sender’s private key and other info provided by the CA
Verified by the recipient through use of the sender’s public key

31. Hybrid Cryptography Systems
Pure asymmetric keys encryption is not widely used except in digital certificates
More widely used as part of hybrid system
Diffie-Hellman Key Exchange method
Exchanging private keys using public key encryption
Asymmetric encryption is used to exchange session keys
Limited use keys
Temporary communications

32. Steganography Process of hiding information
Not technically a form of cryptography
Most popular version
Hiding information within files that appear to contain digital picture or other images
Use one bit per color or 3 bits per pixel to store information.
Compute files that don’t use all available bits

33. Protocols for Secure Communication
Secure Socket Layer (SSL)
Used public key encryption to secure channel
Support by most internet browsers
Client and server establish HTTP session
Client requests access part of web site - requires secure communications
Server sends message to client
Client respond - sending its public key & security parameters
Server finds a public key match
Sends a digital certificate to the client
Client must verify - digital certificate –received, valid & trustworthy
Lasts for duration of session

34. Protocols for Secure Communication
SSL
Two layers of protocol
SSL Record Protocol
Compression, encryption and attachment of SSL header
Received encrypted messages are decrypted and reassembled
Basic security at top level of SSL protocol stack
Standard HTTP
Internet communication services

35. Protocols for Secure Communication
S-HTTP (Secure Hypertext Transfer Protocol)
Extended version of hypertext transfer protocol
Provides for encryption of individual messages between client and server
No session
Designed for sending individual messages

36. Securing E-mail Secure Multipurpose Internet mail Extensions (S/MIME)
Adds encryption of MIME (Multipurpose Internet Mail Extensions)
PEM
Uses 3DES symmetric key encryption and RSA for key exchanges and digital signature
PGP
Pretty Good Privacy
Used IDEA Cipher