Information Security and Management (Abstract) 5

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Presentation transcript:

Information Security and Management (Abstract) 5 Information Security and Management (Abstract) 5. Advanced Encryption Standard 6. Contemporary Symmetric Ciphers Chih-Hung Wang Fall 2011

Famous Symmetric Ciphers AES (Advanced Encryption Standard) Triple DES Other symmetric block ciphers (ex. IDEA、Blowfish、RC5、CAST- 128…etc.)

AES Next generation encryption standard of NIST/FIPS It will replace the use of DES in the following 30 years The sensitive information protected by AES cannot be revealed within 100 years It is selected by the competition from international selection process

Calendar of AES

AES Requirements Block cipher 128-bit block 128/192/256-bit keys It is equal to Triple DES at least on security and is more efficient Provide descriptions and analysis Provide three implementations in two languages (reference and optimized in C，optimized in Java) IF selected, royalty free world wide

The 15 Submission for AES (1)

The 15 Submission for AES (2)

Final AES Selection Rijndael Block cipher with block size 128 bits Accept 128-, 192-, 256-bit length keys Easy to implement in H/W

The Implementation of Crypto Algorithms (W32) http://us.cryptosoft.de/ Different platforms: win16, win32, linux, OS/2,… Triple DES, Rijndael, Safer+, Blowfish, Cast-128, … Old version Crypto++: a C++ Class Library of Cryptographic Primitives Version 5.6.1 (2010/8/9) http://www.cryptopp.com/ Microsoft CryptoAPI

More AES Information NIST AES Homepage AES proposal http://csrc.nist.gov/encryption/aes/ Rijndael Specification Those who are interested in the AES specification (i.e., what will be in the standard) should refer to the Draft FIPS for the AES. Test Values Supporting Documentation Rijndael Developers' Contact Information Rijndael Code: C/C++/Java/Visual Basic FIPS 197 http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf AES proposal http://csrc.nist.gov/archive/aes/rijndael/Rijndael- ammended.pdf

Practice Reading Project Programming/testing Project Rijndael Specification : download from http://csrc.nist.gov/encryption/aes/ Programming/testing Project Download Rijndael source code (C/C++) from Rijndael homepage or other web sites. Modify and refine the source code from web sites such that it can be used to encipher and decipher a message. Write a report that includes the address of web sits, source code and testing results.

Triple DES Double DES

Triple DES Double DES: reduction to a single key It would be possible to find a key K3 such that With 264 possible inputs, how may different mappings? (264)! > (101020) It is reasonable to assume that if DES is used twice with different keys, it will produce one of the many mappings that is not defined by a single application of DES.

Meet-in-the-Middle Attack Works whenever use a cipher twice [DIFF77] Since X = EK1[P] = DK2[C] Attack by encrypting P with all keys and store Then decrypt C with keys and match X value Can show takes O(256) steps

Triple DES Triple DES with two keys C=EK1[DK2[EK1[P]]] P=DK1[EK2[DK1[C]]]

Triple DES Standardized in ANSI X9.17 & ISO 8732 No current known practical attacks The cost of a brute-force key search on triple DES: 2112 (51033) Has been adopted by some Internet applications, eg PGP, S/MIME

Known-Plaintext Attack

Other symmetric block ciphers IDEA International Data Encryption Algorithm A symmetric block cipher developed by Xuejia Lai and James Massey of the Swiss Federal Institute of Technology. One of a number of conventional encryption algorithms that have been proposed in recent years to replace DES. IDEA is included in PGP. 128-bit key to encrypt data in blocks of 64 bits

Other symmetric block ciphers Blowfish A symmetric block cipher developed by Bruce Schneier. Characteristics Fast Compact: can run less than 5K of memory. Simple Variably secure: the key length is variable and can be as long as 448 bits. This allows a tradeoff between higher speed and higher security. 64-bits block cipher

Other symmetric block ciphers RC5 A symmetric encryption algorithm developed by Ron Rivest. Adaptable to processors of different word lengths. Variable number of rounds. Variable-length key Low memory requirement Suitable for smart cards

Comparison