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initial 64-bit X1

initial 64-bit X1

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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Please show explaintation for steps and how CFB mode works along the way thank you.

Consider the following simplified version of the CFB mode. The plaintext is broken into 32-bit pieces: P = [Pı, P2, · … ,], where each P; has 32 bits, rather than the 8 bits used in CFB. Encryption proceeds as follows. An initial 64-bit X1 is chosen. Then for j = 1,2, ·.., the following is performed: C; = P; L32(Ek (X;)) Xj+1 R32(X;)||C; where L32(X) denotes the 32 leftmost bits of X, R32(X) denotes the rightmost 32 bits of X, and X||Y denotes the string obtained by writing X followed by Y. (a) Find the description algorithm. (b) The cipher text consists of 32 bit blocks C1, C2, · ... Suppose that a transmission error causes C1 to be received as C1 7 C1 , but that C2, C3, ·.. are received correctly. This corrupted ciphertext is then decrypted to find plaintext blocks P, P2, P3,.... Show that Pi + P1 but that P; + P; for all i > 4. Therefore the error affects only three blocks of the decryption.
Transcribed Image Text:Consider the following simplified version of the CFB mode. The plaintext is broken into 32-bit pieces: P = [Pı, P2, · … ,], where each P; has 32 bits, rather than the 8 bits used in CFB. Encryption proceeds as follows. An initial 64-bit X1 is chosen. Then for j = 1,2, ·.., the following is performed: C; = P; L32(Ek (X;)) Xj+1 R32(X;)||C; where L32(X) denotes the 32 leftmost bits of X, R32(X) denotes the rightmost 32 bits of X, and X||Y denotes the string obtained by writing X followed by Y. (a) Find the description algorithm. (b) The cipher text consists of 32 bit blocks C1, C2, · ... Suppose that a transmission error causes C1 to be received as C1 7 C1 , but that C2, C3, ·.. are received correctly. This corrupted ciphertext is then decrypted to find plaintext blocks P, P2, P3,.... Show that Pi + P1 but that P; + P; for all i > 4. Therefore the error affects only three blocks of the decryption.
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