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 Used in PGP n Much more difficult than DES RC5 – Family of algorithms n Developed by Ronald Rivest in 1994 n
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