This document discusses different types of ciphers used for encryption. It describes stream ciphers that encrypt data bits using an XOR operation with a keystream. Block ciphers divide data into blocks and encrypt each block separately using keys and an initialization vector. Electronic Code Book (ECB) encryption uses the same key to encrypt each block, revealing patterns, while Cipher Block Chaining (CBC) XORs each plaintext block with the previous ciphertext block before encryption to provide more security.

1. Block Cipher
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2. Contents
• Introduction
• Stream Cipher
• ECB
• CBC
• others
• Closing
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3. Introduction
• Encipherment
o Meaning any mechanism transforming a
data for the unauthorised can’t understand
o Normally a key (pair) is used
o stream cipher and block cipher
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4. Stream Cipher
• Consider data a bit streams
• There is a key stream for encipherment
• The bits and keys are doing exclusive-OR
for each bits
• Faster than block cipher but lower
security
• Ex) LFSR, MUX generator
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5. Block Cipher
• Cut the data into several blocks to do
encipherment
• Keys and IV (Initial Vector) are used
• Slower than stream cipher but appears
higher security
• Ex) DES, AES
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6. ECB (Electronic Code Book)
• Encrypt blocks of plaintext with the key
• Key is already shared beforehand
• Same plaintext produces same ciphertext
so shows low security
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Source: wikipedia

7. CBC (Cipher Block Chaining)
• Reverse operation for decryption with key and
IV
• Can be parallelized because previous
ciphertext block (or IV) is enough for
decryption
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Source: wikipedia

8. CBC (Cipher Block Chaining)
• Exclusiv-ORed block between plaintext and
previous ciphertext are encrypted with
symmetric keys
• IV (Initial Vector) is used at first encipherment
• Slower because encryption should be
sequential
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Source: wikipedia

9. Closing
• Data stream or data block can be
encrypted
• EBC is encryption for plaintext blocks
with keys and have lower security
• CBC is encryption for data blocks which
are exclusive-ORed between plaintext
blocks and previsous ciphertext with keys
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