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5

streamcipher lesson

SEC 2213Based on 462-AC-4B Symmetric Stream Ciphers

Modern Stream Ciphers & RNGs

Stream ciphers encrypt data bit-by-bit, offering extreme speed for real-time applications like GSM and Bluetooth. Master the mechanics of One-Time Pads, PRNGs, and LFSRs.

Stream Cipher

Encrypts bits individually. Like a conveyor belt.
Usage: GSM, Bluetooth, RC4.

  • Extremely Fast
  • No Padding Needed
  • Low Error Propagation (1 bit error = 1 bit error)

Block Cipher

Encrypts chunks (e.g., 64 or 128 bits) at once.
Usage: AES, DES, 3DES.

  • High Diffusion
  • Needs Padding
  • Error Propagation (1 bit error = Whole block trash)

Stream Encryption: Bit-by-Bit XOR

PLAINTEXT
01001000 01000101
KEYSTREAM
11010101 10101010
The keystream generator produces bits continuously to XOR with plaintext.

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