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lecture2 - Lecture 2 Private Key Cryptography CS 392/6813...

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Lecture 2: Private Key Cryptography CS 392/6813: Computer Security Fall 2010 * Adopted from Previous Lectures by Nasir Memon 9/16/2010 Lecture 2 - Private Key Cryptography 2 Course Administration HW#1 due by midnight today Solution will be posted soon HW#2 will be posted by the weekend Would be due in 10 days TA Session for Jon Voris: Email: [email protected] 5-6pm Mondays or Tuesdays (subject to room availability) – please wait for further announcement
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9/16/2010 Lecture 2 - Private Key Cryptography 3 Course Administration -- Partners Please indicate the name of your partner on your HW1 submission In case you are not able to find a partner yourself, please send me an email notifying me about this (if you haven't already done so). Please do this by tomorrow midnight. Instructions to submit team homeworks will be provided a bit later 9/16/2010 Lecture 2 - Private Key Cryptography 4 Outline of today’s lecture Cryptography Overview Private Key Cryptography: Encryption
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9/16/2010 Lecture 2 - Private Key Cryptography 5 Cryptography Etymology: Secret (Crypt) Writing (Graphy) Study of mathematical techniques to achieve various goals in information security, such as confidentiality, authentication, integrity, non- repudiation, etc. Not the only means of providing information security, rather a subset of techniques. Quite an old field! 9/16/2010 Lecture 2 - Private Key Cryptography 6 Private Key/Public Key Cryptography Private Key : Sender and receiver share a common (private) key Encryption and Decryption is done using the private key Also called conventional/shared-key/single-key/ symmetric-key cryptography Public Key : Every user has a private key and a public key Encryption is done using the public key and Decryption using private key Also called two-key/asymmetric-key cryptography
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9/16/2010 Lecture 2 - Private Key Cryptography 7 Cryptography: Cast of Characters Alice (A) and Bob (B): communicating parties Eve (E): Eavesdropping (or passive) adversary Mallory (M): Man-in-the-Middle (or active adversary Trent (T): a trusted third party (TTP) 9/16/2010 Lecture 2 - Private Key Cryptography 8 Common Terminologies Plaintext Key Encrypt (encipher) Ciphertext Decrypt (decipher) Cipher Cryptosystem Cryptanalysis (codebreaking) Cryptology: Cryptography + Cryptanalysis
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9/16/2010 Lecture 2 - Private Key Cryptography 9 Private key model 9/16/2010 Lecture 2 - Private Key Cryptography 10 Open vs Closed Design Closed Design (as was followed in military communication during the World War I/II) Keep the cipher secret Also sometimes referred to as the “proprietary design” Bad practice! (why?) Open Design ( Kerckhoffs' principle ) Keep everything public, except the key Good practice – this is what we focus upon!
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9/16/2010 Lecture 2 - Private Key Cryptography 11 Private Key Encryption: main functions 1.
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