Output FeedBack (OFB)

Similar to Cipher FeedBack (CFB), except:

• Output of encryption function is fed back to shift register in OFB. (CFB: ciphertext unit is fed back to shift register)
• OFB operates on full blocks, not on an $s$-bit subset.

$$C_i=P_i\oplus E(K,(\dots ))\text{ and }{P}_i=C_i\oplus E(K,(\dots ))$$

Nonce

Nonce: time-varying value that has at most a negligible chance of repeating.

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