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CRYPTOGRAPHY

• Cryptology – Science of encryption • Cryptography

Kryptos-hidden Graphein- to write • Cryptanalysis Obtaining original message from encrypted message without knowing algorithms or keys.

• Encryption: Process of converting original message in to form that is unreadable to unauthorized person. Decryption: Process of encrypted text message back in to original form.

Security provided by Encryption Confidentiality: Hide information from unauthorized individuals either in transit or in storage. Interception causes loss of message confidenttality  Integrity: It identifies changes of information either in transit or in storage. Modification causes loss of message integrity.

 ability : Enables authentication of the origin of message and prevents information from repudiating.  Nonrepudiation: It does not allow sender of message to refute the claim of not sending that message.  Access Control  Availability

Physical Cryptography (Weak keys) • Substitution Ciphers: Changing one character/ symbol in to another Transposition Cipher: Transposing or scrambling the letters in a certain manner. Stegnography Process of hiding one message in another. Hybrid Systems

• Substitution Poly alphabatic A B C D E F G……. Plain Text J K L M N O P…… Substitution 1 Q R S T U V W….. Substitution 2 Transposition Cipher( Permutation) From right 1-4, 2-8, 3-1, 4-5, 5-7, 6-2, 7-6, 8-3 00100101 01101011 00001011 10111010

Transposition Ciphers • Rearrange order of characters (permutation) • SIMPLE COLUMNAR CIPHER Using a grid, write plaintext horizontally, read ciphertext. vertically. P

launchmissilesnow launch missil esnow

C

LMEAISUSNNSOCIWHL

• ATTACK ON COLUMNAR CIPHER Ciphertext has same letter frequencies as plaintext -> Easy

• MULTIPLE TRANSPOSITION CIPHERS a plaintext through two or more transposition ciphers -> Much harder to attack.

One-time Pad •

•

Use a random key as long as the message. Must not reuse the key sequence ever again. Both parties must have key sequence

•

Hotline between USA and USSR was rumoured to use a one-time pad.

•

Destroy key sequence after use

•

Advantages?

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Disadvantages?

• EXAMPLE Key is number of places to shift letter K P C

321424 launch OCVREL

• Suggest a good 1-time pad function for binary data?

Transposition Ciphers • Rearrange order of characters (permutation) • SIMPLE COLUMNAR CIPHER Using a grid, write plaintext horizontally, read ciphertext. vertically. P

launchmissilesnow launch missil esnow

C

LMEAISUSNNSOCIWHL

• ATTACK ON COLUMNAR CIPHER Ciphertext has same letter frequencies as plaintext -> Easy

• MULTIPLE TRANSPOSITION CIPHERS a plaintext through two or more transposition ciphers -> Much harder to attack.

Steganography Dear George, March

3rd

Greetings to all at Oxford. Many thanks for your letter and for the Summer examination package. All Entry Forms and Fees Forms should be ready for final dispatch to the Syndicate by Friday 20th or at the very least, I’m told, by the 21st. has improved here, though there’s room for improvement still; just give us all two or three more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy your basic O and A pattern. Certainly this sort of change, if implemented immediately, would bring chaos.

 Conceal existence of message, e.g. 1st letter of each word, least sig. bit of graphic image  Useless once method discovered  Peter Wayner,

Disappearing Cryptography, 2nd ed, Morgan Kaufmann, 2002

Steganography Dear George, March

** 3rd

Greetings to all at Oxford. Many thanks for your letter and for the Summer examination package. All Entry Forms and Fees Forms should be ready for final dispatch to the Syndicate by Friday 20th or at the very least, I’m told, by the 21st. has improved here, though there’s room for improvement still; just give us all two or three more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy your basic O and A pattern. Certainly this sort of change, if implemented immediately, would bring chaos.

Moon beans are nice. Moon

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Nice

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Mathematical Cryptography • HASH Function Mathematical algorithms. Message : this ASCII Values: 116 104 105 115 Calculated value: 232 202 210 230 Hash value Calculation: (232+208+210+230)/10 Hash Value: 88

DES

• Symmetric Algorithms: Both ends of an encrypted message have the same key and processing algorithms. Secret key is generated which is some times called as Private key.  Asymmetric Algorithms: Two keys to encrypt & decrypt data, referred as Public Key & Private key. Public key used by sender to encrypt. Private key is used by receiver to decrypt.

Steganography Dear George, March

** 3rd

Greetings to all at Oxford. Many thanks for your letter and for the Summer examination package. All Entry Forms and Fees Forms should be ready for final dispatch to the Syndicate by Friday 20th or at the very least, I’m told, by the 21st. has improved here, though there’s room for improvement still; just give us all two or three more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy your basic O and A pattern. Certainly this sort of change, if implemented immediately, would bring chaos.

Steganography Dear George, March

3rd

Greetings to all at Oxford. Many thanks for your letter and for the Summer examination package. All Entry Forms and Fees Forms should be ready for final dispatch to the Syndicate by Friday 20th or at the very least, I’m told, by the 21st. has improved here, though there’s room for improvement still; just give us all two or three more years and we’ll really show you! Please don’t let these wretched 16+ proposals destroy your basic O and A pattern. Certainly this sort of change, if implemented immediately, would bring chaos.

 Conceal existence of message, e.g. 1st letter of each word, least sig. bit of graphic image  Useless once method discovered  Peter Wayner,

Disappearing Cryptography, 2nd ed, Morgan Kaufmann, 2002