L16-MOP - Encrypting Long Texts • Message M is divided...

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Encrypting Long Texts Encrypting Long Texts • Message M is divided into L blocks, each consisting of N bits: M = M 1 , M 2 , . . ., M L • Cipher C is constructed in L blocks, each consisting of N bits: C = C 1 , C 2 , . . ., C L • The modes of operation to build the cipher blocks – Electronic Code Book (ECB) – Cipher Block Chaining (CBC) – Output Feedback Mode (OFB) – Cipher Feedback Mode (CFB)
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Electronic Code Book (ECB) Electronic Code Book (ECB) • Each block is encrypted independently –Enc ryp t ion : C i = E K (M i ) – Decryption: M i = D K (C i )
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ECB ECB Advantages: • Small value encryption • Parallel encryption • Parallel decryption • Random Access to blocks Disadvantages: • Identical blocks encrypt the same • No protection on order of blocks • No protection against block loss
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Cipher Block Chaining (CBC) Cipher Block Chaining (CBC) –Enc ryp t ion : C i = E K (M i C i-1 ) – Decryption: M i = D K (C i ) C i-1 M 1 M 2 M n C 1 C 2 C n Encrypt ⊕⊕ Encrypt Encrypt KK K IV Decrypt C 1 C 2 C n
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L16-MOP - Encrypting Long Texts • Message M is divided...

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