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In cryptography, output feedback (OFB) is a mode of
operation for a block cipher. It has some similarities
to the ciphertext feedback mode in that it permits
encryption of differing block sizes, but has the key
difference that the output of the encryption block
function is the feedback (instead of the ciphertext).
The XOR (exclusive OR) value of
each plaintext block is created independently of both
the plaintext and ciphertext.
Output feedback (OFB) is yet another variation on the same theme.
The only difference is that the input to block N+1 is the output of
the block cipher
It is this mode that is used when there can be no
tolerance for error propagation, as there are no chaining
dependencies. Like the ciphertext feedback mode, it uses
an initialization vector (IV). Changing the IV in the same
plaintext block results in different ciphertext. In terms of
error correction, output feedback can tolerate ciphertext
bit errors, but is incapable of self-synchronization after
losing ciphertext bits, as it disturbs the synchronization of
the aligning keystream. A problem with output feedback is
that the plaintext can be easily altered, but using a digital
signature scheme can overcome this problem
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Output Feedback (OFB) is part of