Crytography

1. Crytography Chapter 8

2. Cryptology • Cryptography • 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 • 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 • 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 • 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 • 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: 1 4, 2 8, 3 1, 4 5,5 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