Most, if not all of > > the other ciphers have support for OFB, but AES does not. > > I'll add CFB and OFB as soon as my other patches make it into the > snapshots. Do you need 64-bit, or will 128-bit work? 128-bit. I need aes-128-ofb to start. aes-192-ofb and aes-256-ofb would also be nice down the road.
Counter Mode – The Counter Mode or CTR is a simple counter based block cipher implementation. Every time a counter initiated value is encrypted and given as input to XOR with plaintext which results in ciphertext block. The CTR mode is independent of feedback use and thus can be implemented in parallel. Its simple implementation is shown below: OFB: An IV-based encryption scheme, the mode is secure as a probabilistic encryption scheme, achieving indistinguishability from random bits, assuming a random IV. Confidentiality is not achieved if the IV is a nonce, although a fixed sequence of IVs (eg, a counter) does work fine. 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".
Solved: Keeping The IV Secret In OFB Mode Does Not Make An
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[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 OFB (GNU cryptographic primitives and tools, version 2.0.0) public class OFB extends BaseMode implements java.lang.Cloneable. The Output Feedback (OFB) mode is a confidentiality mode that requires a unique IV for every message that is ever encrypted under the given key. The OFB mode is defined as follows: