Encryption

Encryption - VNSA220 VNSA220 Cyber Self Defense Encryption Erik Golen Bill Stackpole& Daryl Johnson © Daryl G Johnson 2006 What is Encryption

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Unformatted text preview: VNSA220 VNSA220 Cyber Self Defense Encryption Erik Golen Bill Stackpole & Daryl Johnson © Daryl G Johnson 2006 What is Encryption? What is Encryption? • Based on the word “cipher” – an algorithm designed to conceal the meaning of a message. • Definition: the process of obscuring information to make it unreadable without special knowledge, sometimes referred to as scrambling. http://en.wikipedia.org/wiki/Encryption History History • Encryption has been used to protect communications for centuries • Only organizations and individuals with an extraordinary need for secrecy had made use of it • Expensive and slow because done manually History History • Spartan generals • Method secret – Before winding – After winding | | | | H E N T | | | | E I D T | | | | L A E A | | | | P M R C | | | | M U A K – Spiral wound parchment HENTEIDTLAEAPMRCMUAK | | | | History History • Julius Caesar used substitution cipher ABCDEFGHIJKLMNOPQRSTUVWXYZ NOPQRSTUVWXYZABCDEFGHIJKLM • URYYB -> • HELLO • How would you break this • How many combinations? – Letter frequency – Key (letter offset) is secret • Limit to 25 different key values History History • Greeks first to use • • • numerical substitution 34 51 33 41 32 51 13 53 33 43 25 ­> SEND HELP NOW How would you break this? – Letter frequency 1 1 2 3 A F L Q V 2 B G M R 3 C H N S 4 D O T Y 5 E P U Z I/J K • How many combinations? 4 – Table secret 5 • 1.4 * 10^25 key values WX When do you use encryption? When do you use encryption? – Turn on your cell phone – Check voice / email (PGP) – Use debit / credit cards (Hopefully) – Order PPV movies – Drive on the thruway (EZPass) – Online gaming – Visit your doctor (Kind of) … But do you REALLY need it? But do you REALLY need it? • • • • • To do your banking? To purchase an item? On your cell phone? On your computer? For everyday conversation? No encryption required No encryption required • • • • • Purchase with cash Deposit/withdrawal at teller Don’t use wireless phone Speak in private If your communications do not pass through an insecure channel Questions Questions • Is your communication/data sensitive? – Is there value you don’t realize? – Is there something there that I don’t want someone else to get? – How do you know? – Can you be sure? • Is the channel public/private? Why use encryption? Why use encryption? • • • • • Hide communications or information Ensuring privacy Ensuring confidentiality Lack of trust Your communications or information must pass through some insecure area (e.g., internet) Goals of Cryptography Goals of Cryptography • Privacy • Authentication • Integrity – Keep private content private – You’re talking to who you think you’re talking to • Digital Signatures – Ensure the content SENT is the content RECEIVED • Non­Repudiation • One­way hash functions – Binding the transaction (prevents party from claiming they were not part of the transaction) Ethics of Encryption Ethics of Encryption • Who has access to high grade, uncrackable encryption? – You, your buddies, friends, siblings, parents, and grandparents – The US Government & its agencies (FBI, CIA, NSA, etc) local & state law enforcement, the military – Other governments & their militaries, people you may not like or may not WANT to have access – Your doctor, lawyer, teachers, grocer, butcher – Those you or your government considers terrorists or your enemy – EVERYONE Is this availability a GOOD thing? Is this availability a GOOD thing? • Balance – public interest and public safety with/against – right to privacy/right to free expression Recent History Recent History • 1976 ­ Diffie­Hellman– Introduced the concept of Public • Key Cryptography in their paper titled “New Directions in Cryptography“ – also introduced a new key­exchange mechanism (diffie­hellman key exchange) 1978 ­ Rivest, Shamir & Adleman –provided practical public key encryption / signature scheme (now referred to as RSA) – Security is based on complexity of factoring HUGE prime numbers • 1985 – ElGamal – alternative public key scheme (powerful and practical as well) Recent History Recent History • 1991 – First international standard for – Based on RSA digital signatures (ISO/IEC 9796) adopted adopted by US Govt. (Based on ElGamal standard) • 1994 – Digital Signature Standard (DSS) Recent History Recent History • 1991 – Pretty Good Privacy (PGP) published via CompuServe by Phil Zimmermann – – – Designed as a human­rights tool Leveraged RSA public­key scheme Started a three­year criminal investigation • US BATF Export restrictions on “munitions” were violated • Dropped in 1996 – Became most widely­used email encryption software in the world. – Current product “zfone” – end­to­end VoIP telephony encryption How does it work? (mechanics) How does it work? (mechanics) • Substitution ­ exchange one thing for • • • • • another Transposition ­ change the order One time pad (codebook) Block cipher Stream cipher (one at a time) Hash – – Digital Fingerprint Hash (vb.) How does it work? (cont.) How does it work? (cont.) • All types require the use of a KEY • Use of cryptography assumes some understanding of the cryptographic functions and risk of being broken I have written this book partly to I have written this book partly to correct a mistake. One Time Pads One Time Pads • • ILWTY NQUVC XBCVM YNEIW GFTKQ QTAXB RLLRC MSNTO FNBAF CIERD UAHAD JVULW CLORV LGPBY CATXC QCWBJ QYRUJ YEAYY LVPSW OTZMH • Problem­­Transposition & substitution use the same key over and over for each letter Can lead to frequency analysis OTPs provide a list of key values – – – – • Drawback ­ Must be as long as the message you want to encrypt, making it impractical Enough for a different key for each letter Can not do freq analysis “perfect secrecy” – cipher gives no added info http://www.alpharubicon.com/elect/otptoboe.htm Encryption categories Encryption categories • Symmetric key encryption • Asymmetric key encryption Symmetric key encryption Symmetric key encryption • Two parties share an identical key • Key used to ENCRYPT data is same as key used to DECRYPT data • K = key, D = data, C = ciphertext (encrypted data) • Mathematically commutative • f(D)K=C, f(C)K=D – (you remember commutative, right?) Asymmetric key encryption Asymmetric key encryption • AKA public key cryptography • Three keys – – – One “public”, one “private”, one symmetric Document to be sent is encrypted with symmetric key Symmetric key is encrypted with public key of recipient – PRIVATE key of recipient is used to decrypt the symmetric key, which is then used to decrypt the document. – Locked mailbox with mail slot – Digital Signature — Wax seal • Two analogies Public Key Infrastructure Public Key Infrastructure • Issue is ensuring the public key hasn’t been • tampered with Digital Certificates are PKI – Use Trusted Third Party to hold / distribute / validate keys. Public key servers Public key servers • Store copies of public keys • Allow individualsto search for posted public keys • How do you determine key validity? (see next slide) Public key servers Public key servers Breakable? Breakable? • • • Time Complexity Not if but when! ...
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This note was uploaded on 05/27/2009 for the course NSSA 4050-220 taught by Professor Golen during the Fall '08 term at RIT.

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