Module Four

N data within a file does not have to be encrypted in

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n Data within a file does not have to be encrypted in a certain order. n Used for small amounts of data, like challenge-response, key management tasks. n Also used to encrypt PINs in ATM machines. Cipher Block Chaining n Each block of text, the key, and the value based on the previous block is processed in the algorithm and applied to the next block of text. Cipher Feedback n The previously generated ciphertext from the last encrypted block of data is inputted into the algorithm to generate random values. n These random values are processed with the current block of plaintext to create ciphertext. n This mode is used when encrypting individual characters is required. Output Feedback n Functioning like a stream cipher by generating a stream of random binary bits to be combined with the plaintext to create ciphertext. n The ciphertext is fed back to the algorithm to form a portion of the next input to encrypt the next stream of bits. DES has been broken with Internet network of PC’s DES is considered vulnerable by brute force search of the key – replaced by triple DES and AES Triple DES n Double encryption is subject to meet in the middle attack n Encrypt on one end decrypt on the other and compare the values n So Triple DES is used n Can be done several different ways: n DES – EDE2 (encrypt key 1, decrypt key 2, encrypt key 1) n DES – EE2 (encrypt key 1, encrypt key 2, encrypt key 1) n DES –EE3 (encrypt key 1, encrypt key 2, encrypt key 3) - most secure n Advanced Encryption Standard n Block Cipher that will replace DES n Anticipated that Triple DES will remain approved for Government Use n AES announced by NIST in January 1997 to find replacement for DES 5 Finalists n MARS n RC6 n Rijndael n Serpent n Blowfish
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October 2, 2000 NIST Selected Rijndael 2 Belgian Cryptographers Dr. Daeman and Dr. Rijmen Will be used by government for sensitive but unclassified documents Rijndael Block Cipher n Resistance to all known attacks n Design Simplicity n Code compactness and speed on wide variety of platforms n Iterative block cipher with variable block length and key lengths that can be independently chosen as 128, 192 or 256 bits. n 3.4 x 10 38 possible 128 bit key combinations n 6.2 x 10 57 possible 192 bit key combinations n 1.1 x 10 77 possible 256 bit key combinations n Intermediate cipher result is called “state” that transformations operate on n Does not use Feistel transposition structure from DES n Uses round transformation of 3 layers n Non-linear layer n Linear mixing layer n Key addition layer n Suitable for High Speed Chips and compact co-processor on smart cards Twofish n 128 bit blocks in 16 rounds, up to 256 bit keys n Developed by Counterpane based on Blowfish (also by Counterpane) - Bruce Schnier n Employs whitening before first round and after second round n Need to break whitening keys in addition to Twofish key n Transposition IDEA Cipher - International Data Encryption Algorithm n 64 bit block, 8 rounds, and 128 bit keys n
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n Data within a file does not have to be encrypted in a...

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