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- 1A more sophisticated encryption approach n substitution ciphers, M1
,M2
,…,Mn
cycling pattern:
• e.g., n=4: M1
,M3
,M4
,M3
,M2
; M1
,M3
,M4
,M3
,M2
; ..
for each new plaintext symbol, use subsequent
substitution pattern in cyclic pattern
• dog: d from M1
, o from M3
, g from M4
Encryption key: n substitution ciphers, and cyclic
pattern
• key need not be just n-bit pattern - 2Symmetric key crypto: DESDES: Data Encryption Standard
US encryption standard [NIST 1993]
56-bit symmetric key, 64-bit plaintext input
block cipher with cipher block chaining
how secure is DES?
• DES Challenge: 56-bit-key-encrypted phrase decrypted
(brute force) in less than a day
• no known good analytic attack
making DES more secure:
• 3DES: encrypt 3 times with 3 different keys - 3AES: Advanced Encryption Standard symmetric-key NIST standard, replaced DES
(Nov 2001)
processes data in 128 bit blocks
128, 192, or 256 bit keys
brute force decryption (try each key) taking 1 sec
on DES, takes 149 trillion years for AES - 4—
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- Fichas sobre Sin título, creado por luke daniels el 11/06/2017.
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- luke daniels
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