Triple-DES with Three-Keys  although are no practical attacks on two- key, Triple-DES has some drawbacks  can use Triple-DES with Three-Keys to avoid even these  C = EK3(DK2(EK1(P)))  has been adopted by some Internet applications, eg PGP, S/MIME
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Triple-DES with Two-Keys  hence must use 3 encryptions  would seem to need 3 distinct keys  but can use 2 keys with E-D-E sequence    C = EK1(DK2(EK1(P))) because encrypt & decrypt equivalent in security if K1=K2 then can work with single DES  standardized in ANSI X9.17 & ISO8732  no current known practical attacks
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Double DES?  Using two encryption stages and two keys  C=Ek2(Ek1(P))  P=Dk1(Dk2(C))  It is proved that there is no key k3 such that  C=Ek2(Ek1(P))=Ek3(P)  But Meet-in-the-middle attack Cryptography and Network Security 151
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Different Keys for Encryption and Decryption • • • • • Encryption key, K1 Decryption key, K2 Ek1(M) = C Dk2(C) = M Dk2(Ek1(M)) = M Decryption Key Encryption Key Plaintext Ciphertext Encryption Decryption Original Plaintext
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Pretty good privacy (PGP)  Internet e-mail encryption scheme, de-facto standard.  uses     symmetric key cryptography (triple-DES, CAST, or IDEA) public key cryptography (RSA) hash function (MD5 or SHA) and digital signature as described. A PGP signed message: ---BEGIN PGP SIGNED MESSAGE--Hash: SHA1 Bob:My husband is out of town tonight.Passionately yours, Alice ---BEGIN PGP SIGNATURE--Version: PGP 5.0 Charset: noconv yhHJRHhGJGhgg/12EpJ+lo8gE4vB3mqJh FEvZP9t6n7G6m5Gw2 ---END PGP SIGNATURE---  provides secrecy, sender authentication, integrity. Network Security 7-27
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Encryption/Decryption Decryption Key Encryption Key Plaintext Ciphertext Encryption M Decryption C EK1(M) = C Original Plaintext M DK2(C) = M DK2(EK1(M)) = M
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So…Where Have You Been? In this assignment, I would like you to help me compile a composite profile of Thinking Geographically students’ geographic experience. Attached are three blank maps: one of Virginia’s localities; one of the United States; and one of the world (with enlarged insets for Europe and the Middle East). On each, shade in all of the localities, states, and countries you have traveled through or visited. You must have been on the ground in each locality, state, or country; airport layovers or airport hotel stays and travel through by train do not count!. Use whatever kind of marker you like (I prefer the medium highlighters with sharp and wide surfaces, but marking pens that won’t bleed through, colored pencils, and even crayons will do), as long as it’s easily seen on the maps. Virginia map – (1) color-in the localities you have been in and/or through. You may need to consult a Virginia highway map to figure out which Commonwealth localities you’ve experienced. For example, if you’ve been from Fairfax County to Longwood via US 15, from north to south, you’ve been through Fairfax, Prince William, Fauquier, Culpeper, Madison, Orange, Louisa, Fluvanna, Buckingham, and Prince Edward Counties. From the City of Richmond to Virginia Beach via I-64, I-664, and I-264/Virginia Beach Expressway, you would have been in Richmond City, Henrico, New Kent, James City, and York Counties, and Newport News, Hampton, Norfolk, and Virginia Beach Cities. All of the places you’ve been in Virginia should be contiguous (strung together) unless you flew/parachuted in, came in by boat, or snuck in through a neighboring state. If you’ve been to all but a handful of localities, you may mark those you have not been to, as long as you make a note of that on the map. (2) count up and record the number of localities you have been to/through, divide that number by 133, multiply by 100, and record the percentage of localities you’ve been to in the space provided (all told, you’ve probably been to more of Virginia than you realize – that’s part of the point of this!); (3) write in what you consider your home locality (probably where you graduated high school) in the space provided and indicate it with a darker color or black on the map (if you’re from out-of-state, just leave it blank); (4) check the appropriate box for urban/suburban/small town/rural (be aware that just because your locality has the work “city” in its title doesn’t necessarily mean it’s urban – which means built-up); and (5) use a line pattern to indicate the locality you most want to begin your teaching career in. US map – (1) color the states you’ve been to/through (remember: airports and train travel don’t count), darken/blacken in your home state; (2) write in your birthplace state (for most of you, that probably will be Virginia) in the space provided and blacken/darken it in on the map; (3) tally and record the number of states you’ve been to/through (including the District of Columbia and your home state), divide by 51, multiply by 100, and that’s the percentage of states you’ve been to and enter that number in the space provided; (4) with a horizontal line pattern for your father and a vertical line pattern for your mother, mark your parents’ birth states on the map (if it’s the same state, you’ll have a crisscrossed pattern) World map – (1) color the countries you’ve been to other than the U.S. (even if you’ve only been to a coastal resort, you’ve been to that country, but again, airport layovers don’t count); (2) tally and record the number of countries other than the U.S. that you’ve been to, divide by 205, multiply by 100, and that’s the percentage of countries other than the US that you’ve visited. Enter that number in the space provided. I’ve provided inset maps for Europe and the Middle East that show more detail if you’ve been to a small country that’s difficult to see. If you’ve been to an island country too small to be seen, list those on the map. You do not need to mark the U.S. on this map. I will tally up the total results and produce maps showing the percentage of students across all three sections who have been to/through particular Virginia localities, U.S. states, and other countries. This will give us an idea of how well-traveled you all are. Value: up to 15 points (12 necessary items, one point each + 3 possible neatness points) Due date: Wednesday, February 10, 2016 DO NOT INCLUDE THIS COVER SHEET WHEN YOU HAND THE MAPS IN! 1
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Pretty good privacy (PGP)  Internet e-mail encryption scheme, defacto standard.  uses symmetric key cryptography, public key cryptography, hash function, and digital signature as described.  provides secrecy, sender authentication, integrity.  inventor, Phil Zimmerman, was target of 3-year federal investigation. A PGP signed message: ---BEGIN PGP SIGNED MESSAGE--Hash: SHA1 Bob:My husband is out of town tonight.Passionately yours, Alice ---BEGIN PGP SIGNATURE--Version: PGP 5.0 Charset: noconv yhHJRHhGJGhgg/12EpJ+lo8gE4vB3mqJ hFEvZP9t6n7G6m5Gw2 ---END PGP SIGNATURE--- 8: Network Security 8-71
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Double-DES?  could use 2 DES encrypts on each block  C = EK2(EK1(P)) issue of reduction to 1-DES; “is DES a group?”  Campbell, Wiener in 1992: NO!  “meet-in-the-middle” attack        works whenever use a cipher twice since X = EK1(P) = DK2(C) attack by encrypting P with all keys and store then decrypt C with keys and match X value Basic round of the attack takes 2 * 256 encryptions/decryptions; we may have to repeat it a few times. Show on board
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