Output Feedback Mode (OFB)

• An initial vector is encoded N times
• The result of each encoding is used to XOR a message block
• Allow pre-computing of pseudorandom stream
• No error propagation problem as in CBC
• Allow in-time encrypt/decrypt due to bit-wise computation
• Subject to known-plaintext substitution attacks:
  Knowing P_i allows you to recover K_i and substitute C_i with C_i'

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 Last change: Saturday, June 7, 2003 11:47 am
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