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Questions tagged [ofb]

Output Feedback Mode (OFB) is an encryption mode, that builds a synchronous stream-cipher from a block-cipher.

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1answer
26 views

How many bytes of the last keystream block are used to XOR the final block of partial plaintext in CFB, OFB & CTR modes?

I apologize if this is a dumb question but I'm trying to understand how the final block of partial plaintext is XORed using only n number of bytes in the final keystream block. How do we determine ...
4
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1answer
191 views

Is it ok to transmit an IV as a custom HTTP header?

Considering an AES OFB encryption algorithm, suppose that I'm sending a message over HTTP (not HTTPS) and my message body contains the cyphertext. I'd like to know if transmitting a random ...
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1answer
58 views

What (if any) information can an eavesdropper infer in this scenario when using DES in OFB mode?

Assume that a company wants to use DES in order to encrypt messages to remotely control its manufacturing machines. The company uses different messages types of 8 ASCII characters length each. The ...
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1answer
762 views

What is the advantage of CFB over OFB?

I was wondering if CFB can be better than OFB in any ways. I would like to know in what cases one would use CFB over OFB.
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1answer
500 views

AES in OFB mode and IVs

I'm trying to understand cryptosystems and their implementations to understand how to properly implement them. I have a function implementing AES-128 in OFB mode. Let's call it ...
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1answer
2k views

OFB mode and CFB mode error propagation in 64bits

I am trying to understand (in simple terms), how error propagation works in the transmission of ciphertext in both OFB and CFB using a 64bit mode. I am having a hard time understanding the ...
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1answer
127 views

Security of OFB mode if PRP is used instead of PRF

In the cryptography lecture at my university, we had the theorem that (randomized) OFB mode is IND-CPA secure if the used pseudorandom function (PRF) is IND-PRF secure. Afterwards, we investigated ...
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1answer
399 views

Is AES in OFB mode with same IV more robust than ECB mode?

I am looking at implementing AES128 bit encryption of a data stream. Since AES128 is a block cipher, which is inherently less robust than a stream cipher, I have considered configuring AES128 as a ...
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1answer
2k views

Is there a way to encrypt an integer within an arbitrary range?

I need an algorithm that can take an integer, an arbitrary range, a key of 16/24/32 bytes, and an initialization vector of 16 bytes(ideally), and return an integer in the same range. My latest attempt ...
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1answer
455 views

Implementing 5 modes of operation with a hash function

Is it possible to implement any of the 5 modes of operation (ECB, CBC, OFB, CFB, CTR) with a hash function?
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2answers
6k views

What are the advantages of using OFB (Output Feedback Mode)? [closed]

I have a problem with OFB mode, because I have heard that it is stronger than CFB.
3
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1answer
407 views

Is MCrypt's 8-bit OFB mode secure?

I just stumbled across a Stack Overflow post which points out that the libmcrypt library (notably used in PHP) implements a somewhat unusual set of block cipher modes: it calls the usual CFB and OFB ...
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1answer
455 views

CTR_DRBG versus OFB_DRBG

As far as I know, in the development of ANSI X9.82, there was consideration of OFB_DRBG, a pseudorandom number generator based on block ciphers like CTR_DRBG, but it appears to have been rejected of ...
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1answer
122 views

With wrong IV at receiver side, the CFB in better than OFB?

Assume the receiver have a wrong IV (initialization vector), in the CFB mode only the first block of plaintext is wrong but in OFB mode the second and all blocks will be affected. Is that correct? ...
4
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1answer
2k views

What's the advantage of using OFB/CFB/CTR modes over a stream cipher

As far as I understand: The primary disadvantage associated with stream ciphers is the need for a random and unique key for each run in order to protect against reused-key attacks. OFB/CFB/CTR block ...
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1answer
819 views

crypto design with AES256 MODE OFB

I have the following APP Design key store (contains 1:n user payload as 1:n key store entries) key store salt (is used to extend to key store password to 256 bits, stored in clear text) key store ...
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2answers
1k views

May the problem with DES using OFB mode be generalized for all feistel ciphers

There is a problem with using DES as the block cipher in OFB mode, eg: the feedback that goes back into the next round will be encrypted with the same key $k$ resulting back into the plaintext IV used ...
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3answers
418 views

How comparable is OFB to a one-time pad?

This is a rather trivial question, I just want to see if I get the concept right. In OFB you generate a pseudorandom stream based on some nonce, and you XOR that with the message to get the ...
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2answers
582 views

Is the Blum Blum Shub PRNG suitable to create initialization vectors?

Is it a good idea to use a Blum Blum Shub Generator to create my initialization Vector (IV) in AES-OFB (Output Feedback Mode)?
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1answer
394 views

Probability of Repeated Encrypted Block In Output Feedback (OFB) Mode

Is there any probability/chances of repeated encrypted block in Output Feedback (OFB) mode? Is there any existing documentation/studies about that? If it is existing, can you please provide me a link ...
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2answers
1k views

Capacity of Advanced Encryption Standard in terms of File Encryption

what is the capacity of AES in terms of File Encryption? is it really good to encrypt a large files in AES? ex. I am encrypting a 8GB of File... is it still good to used AES? is it still good to used ...
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4answers
2k views

Is my pseudo-random initialization vector secure?

How can I know if I am generating a secure pseudorandom initialization vector? Currently I am planning to generate a pseudo-random initialization Vector using current date and time - is this secure ...
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3answers
3k views

Which attacks can be avoided by the use of OFB instead of ECB?

For a file encryption program, I was told to use Output Feedback mode (OFB) instead of ECB (Electronic code book) mode. Which attacks can I avoid by this choice?
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2answers
839 views

Complexity of ECB and OFB

What is the complexity of ECB in terms of Time and Memory? and also in OFB? I can't find it in the internet, so I decided to ask it in here.
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1answer
2k views

How does Output Feedback mode use the initialization vector?

How can I process Initialization Vector inside the Block Cipher Encryption box (using for example AES) together with the Key? Will I encrypt the Initialization Vector like a block of plaintext? So I ...