Stacey Levine. History of cryptography Why cryptography? Private Key Systems Public Key Systems Comparisons and PEM (not) The future - Quantum Cryptography.

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Presentation transcript:

Stacey Levine

History of cryptography Why cryptography? Private Key Systems Public Key Systems Comparisons and PEM (not) The future - Quantum Cryptography

Earliest recorded us around 1900BC in Egypt Around 100BC Julius Caesar used substitution cipher 1623 – Sir Francis Bacon described bilateral cipher A type of steganography (hiding) Lots of other uses/advances – most notable Enigma machine in WWII 1970’s - Dr. Horst Feistal invented DES 1977 magazine The Scientific American – RSA announced 2007 Quantum Cryptography successfully used to transmit 50 miles [8]

Message passing between authenticated principals Authenticate message has digital signature

Encryption algorithm E turns plain text message M into a cipher text C C=E(M) Decrypt C by using decryption algorithm D which is an inverse function of E M=D(C)

Confidentiality kept by keeping algorithms secret. Not practical over distributed systems – too many algorithms. Solution is to decompose algorithm Function - public Key - private

Encryption algorithm with secret key Ke Decryption key Kd M=D kd ( E ke (M)) Requirements of function (algorithm) Different messages with same key  distinct result Same message different key  distinct results Key impossible to infer from plaintext/ciphertext

The keys Ke and Kd are different, but it is convenient to choose a key K that can be applied to both. The longer the key (the more bits) the more secure it is

DES – developed by IBM  56 bit key – sufficient because 2 56 =7.2 *  According to the book this too large to enumerate with modern computers but our book is from 1998  The plaintext is broken down into 64 bit blocks  Each block is encrypted using the key  Drawback is that if blocks are repetitive in plaintext, so will the ciphertext be giving a clue to the interlopers.  This can be addressed with chaining – each block is XOR’d with previous encrypted block BEFORE encryption.

Private key systems require [n*(n-1)]/2 keys Keys must be agreed on before secure communication can start. The keys can be distributed in a key distribution system which will be covered next week.

Introduced by Diffie and Hellman Each principal keeps a set of encryption keys ( Ke & Kd ) Encryption algorithm E is public and so is the key Ke Decryption algorithm D and decryption key Kd is kept private. Data sent to a principal is encrypted using that persons Ke

Basically a two key system It is possible to make E and D public if Ke and Kd are kept private and impossible to infer RSA uses this approach E and D are public. And are inverse of each other. Relies on computational complexity in factoring large numbers upon which keys are placed.

 Message is limited to k size bits  Integer k is chosen such that 2 k < N  N =p * q where p & q are LARGE prime numbers  Kp (public encyrption key) and Ks (private decryption key) are derived from p & q

 Private Key DES is computationally efficient  Public Key RSA is computationally expensive  Possible best use is RSA for short/important data and DES for long or less critical  Privacy Enhanced (PEM) initiative does this (NOTE: this is gone now..) – basically used certificates  PGP took over

 Based on Quantum theory  The act of observing affects what is being observed  Schrodinger’s Cat  quantum indeterminacy or the observer's paradox

Al Sends Message Bob Gets Message Interloper

1. Chow, Randy; Johnson, Theodore; Distributed Operating Systems & Algorithms, [April 2007] 3. What is Quantum Physics, 4. Elliott, C., Pearson, D., and Troxel, G Quantum cryptography in practice. In Proceedings of the 2003 Conference on Applications, Technologies, Architectures, and Protocols For Computer Communications (Karlsruhe, Germany, August , 2003). SIGCOMM '03. ACM Press, New York, NY, DOI= 5. Papanikolaou, N An introduction to quantum cryptography. Crossroads 11, 3 (May. 2005), 3-3. DOI= 6. Diffie, W Ultimate cryptography. Commun. ACM 44, 3 (Mar. 2001), 84. DOI= 7. Components for quantum cryptography Zbinden, H.; Ribordy, G.; Stucki, D. Optical Fiber Communication Conference, 2006 and the 2006 National Fiber Optic Engineers Conference. OFC 2006, Vol., Iss., 5-10 March 2006 Pages: 3 pp.- 8. E.S.;”Hack-Proof Internet”, Popular Science Magazine, February 2007, pg (April 2007)