OFB (Output FeedBack) as a Stream Cipher
The OFB mode requires that the IV is a nonce, i.e., the IV 33 * must be unique for each execution of the mode under the given key. 34 * Refer to SP 800-38A for more details OFB 3: The Output Feedback (OFB) mode processes small increments of plain text into cipher text instead of processing an entire block at a time. This mode is similar to CFB; the only difference between the two modes is the way that the shift register is filled. If a bit in the cipher text is mangled, the corresponding bit of plain text will be It is recommended to use NOFB mode rather than OFB mode. MCRYPT_MODE_NOFB (output feedback, in n-bit mode) is comparable to OFB mode, but operates on the full block size of the algorithm. MCRYPT_MODE_STREAM is an extra mode to include some stream algorithms like "WAKE" or "RC4". This is a weird assertion. A block cipher in OFB mode is, functionally, a stream cipher which produces a key-dependent stream of pseudorandom bytes; encryption is then just a XOR of the stream with the data to encrypt (and decryption is identical). Jul 21, 2020 · OFB mode (see Figure 6) is similar to the CFB mode except that the quantity exclusive-ored with each plaintext block is generated independently of both the plaintext and ciphertext. An initialization vector s 0 is used as a "seed" for a sequence of data blocks s i , and each data block s i is derived from the encryption of the previous data
[2010-02-25 18:18 UTC] zelnaga at gmail dot com mcrypt also seems to be implementing OFB and CFB modes identically. Although the first block produced by either mode should be the same, subsequent blocks should be different. ie. in CFB, the second block is XOR'd with the previous ciphertext, reencrypted with the key, whereas in OFB, the second block is XOR'd with that which the previous text
The OFB mode uses an initial chaining vector (ICV) in its processing. OFB mode requires that the ICV is a nonce (the ICV must be unique for each execution of the mode under the given key). Each encryption step takes an input block, enciphers it with the key provided to generate an output block, and then exclusive ORs the output block with the OFB mode is which is output feedback mode, each block ciphertext is generated by this way: use the IV encrypt with the key, then xor the output with the plaintext, in the next step, the value to encrypt with the key is the output of previous step before xor with plain text (which is feedback mechanism) This section describes what is OFB (Output FeedBack) Operation Mode - each plaintext block is XORed with the current output block to be the ciphertext block. The current output block is the encrypted version of the previous output block. OFB (Output FeedBack) operation mode can be described with notations defined earlier as the following AES encryption is a web tool to encrypt and decrypt text using AES encryption algorithm. The tool is free, without registration.
Finally review modern block cipher modes, such as cipher block chaining (CBC), cipher feedback (CFB), output feedback (OFB), and counter (CTR), which can help authenticate large amounts of …
[2010-02-25 18:18 UTC] zelnaga at gmail dot com mcrypt also seems to be implementing OFB and CFB modes identically. Although the first block produced by either mode should be the same, subsequent blocks should be different. ie. in CFB, the second block is XOR'd with the previous ciphertext, reencrypted with the key, whereas in OFB, the second block is XOR'd with that which the previous text