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Crytography Chapter 8. Cryptology  Cryptography  Comes from Greek  Kryptos meaning “hidden”  Grahein meaning “to write”  Process of making and using.

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Presentation on theme: "Crytography Chapter 8. Cryptology  Cryptography  Comes from Greek  Kryptos meaning “hidden”  Grahein meaning “to write”  Process of making and using."— Presentation transcript:

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 3 rd 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

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