Information security

Stream Vs Block Cipher

Stream Cipher
⚫ Process: Encrypts a digital data stream one bit or one
byte at a time
⚫ Type: Symmetric key cipher (same key used for
encryption and decryption)
⚫ Key Feature: Uses a generated key stream in the form
of bits.
⚫ A key stream (e.g., K₀ = 01001) is generated.
⚫ This key stream is combined with the plaintext (bit by
bit) using an algorithm
⚫ Typically uses XOR operation between key stream and
plaintext
⚫ Same process is applied in reverse for decryption

, Stream Vs Block Cipher

Stream Cipher
Encryption:
⚫ Messsage = 10110110
⚫ Key= 01010101
⚫ Cipher= 11100011


Decryption: C 11100011
Key : 01010101
Message : 10110110

, Stream Vs Block Cipher

Block Cipher
⚫ Process: Encrypts a fixed-length block of plaintext as
a single unit
⚫ Input/Output: Processes entire blocks to produce
ciphertext blocks of equal length
⚫ Common Block Sizes: 64 bits or 128 bits
⚫ Evolution: Modern block ciphers have replaced
classical ones (like Playfair)
Key Characteristics:
⚫ Treats plaintext in fixed-size blocks rather than individual bits/bytes
⚫ Same algorithm used for encryption and decryption (symmetric)
⚫ Provides stronger security through diffusion and confusion
Plaintext 64 bits 64 bits