Questions tagged [ctr]

Counter Mode (CTR) is an encryption mode, that builds a random-access stream-cipher from a block-cipher.

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Does keeping IV secret increase security of CTR mode?

Let's suppose I encrypt something with CTR mode and keep the key and IV secret. Does keeping the IV secret together with the key increase strength of encryption?
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Proper use of AES CTR

I've read that AES CTR is only safe if used properly. Therefore, I want to be sure that I use it properly. The initial vector (IV) can only be used once, it doesn't have to be random. Is it secure to ...
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CTR and OFB block cipher modes and their post-quantum security. Some questions [duplicate]

It's said that quantum computers can break block ciphers with 2^(n/2) queries (being n the key size). I read this paper: https://eprint.iacr.org/2016/197 It says that CTR and OFB modes are safe ...
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Size of the counter in CTR mode

If I understood it correctly, in CTR mode I encrypt the nonce or IV together with the counter as a block, which is then XORed with the plaintext. For the next block, I increment the counter. Is there ...
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What does counter mean in Counter (CTR) Mode? Is it the same as nonce?

As asked above, what does "counter" mean exactly? Is it the same as nonce? Also, the book Network Security Essentials (6ed.) from William Stallings states, "Typically the counter is ...
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How to produce Auth Data and tag in GCM? Does MAC appended CTR mode encrypted text weaker than GCM?

In https://en.wikipedia.org/wiki/Galois/Counter_Mode, there's a diagram which tells us how GCM works in general. I have watched computerphile video on how ECB,CBC and CTR mode works and able to ...
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How is WinZip AES different from normal AES

I'm trying to write a function in dart that can can decrypt a file inside a zip that is encrypted using the WinZip AES-256 standard. Documentation I have found here: https://www.winzip.com/en/support/...
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CTR mode calculate messages before new key is required

I am studying a cryptography video on Coursera here titled: Modes of Operation: Many Time Key (CTR). I have just two simple questions: At around 4:30 in the video they show 2^48 without saying where ...
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226 views

CTR overlap with random IV

Problem: I'm slightly worried about counter repeats in CTR mode when using random IV. If you split it (like half IV, half counter), it increases chances of same IV (it is smaller) and limits message ...
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222 views

How to use nonce, counter, and IV in AES-256-CTR?

preface: i am not cryptographically savvy. there are similar questions on this board but they do not give the answer i need. how do i construct a valid IV, given a nonce? What does this have to do ...
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Do some Block Cipher Modes encrypt the nonce and then XOR it with the data?

Reading https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Counter_(CTR) it looks like CTR (and some other modes) encrypt the nonce (plus count, for CTR) rather than the plaintext. The ...
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Why is xor'ing plaintext blocks and encrypting the resulting checksum not a secure MAC using CTR mode? [closed]

Consider message $P$ being split into $n$ blocks that match the block size of the underlying block cipher. The message has fixed length and the length is always a multiple of the block size. ...
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Mismatch between NIST SP800-90A test vectors and CTR_DRBG output

I am testing my Python implementation of NIST SP800-90A CTR_DRBG https://csrc.nist.gov/publications/detail/sp/800-90a/rev-1/final (AES-256, no df) with the CAVP test vectors (https://csrc.nist.gov/...
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Hashing function as a cipher in CTR mode [duplicate]

Can we use hashing function in CTR mode as a cipher? And our key could be a random initialization vector. Are there any practical problems with that idea, that we don't do this?
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Simple XOR cipher with pseudo random plain text of arbitrary length

We all know that simple repeated XOR cipher over plaintext is trivially vulnerable to known plaintext attack, even when just a part of plain text is known and even to ciphertext only attack if you ...
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Is multiple encryption with CTR mode vulnerable to meet-in-the-middle attacks?

Let's suppose I want to encrypt my disk partition with AES-256 in CTR mode 2 times using two different keys and IVs. Will I get 512 bits of encryption strength?
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Comparing the security when using fixed IV for CBC and CTR

Assuming that I'm using fixed IV's for CBC mode and CTR mode. I know that in CBC, the blocks depend on the previous ones and on CTR they are all independent. Yet with the same key and fixed IV, the ...
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1answer
146 views

CTR block generation

From what I understand, CTR works by taking a counter, concatenating it with a nonce, and encrypting the result, which gets XORed to the ciphertext. For a 128-bit block cipher (ie. AES), my ...
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Brute force strategy

I am a beginner in this field, and I was thinking about brute force strategies to break symmetric key encryption. Let's say we have a block cipher in CTR mode and the key is 56 bits in size. What ...
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AES-128/CTR/NoPadding HMAC vs Signature

Is there a semantic difference between tagging AES_128/CTR/NoPadding ciphertext with a MAC (HmacSHA256) or Digital Signature (<...
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1answer
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Cryptography Engineering - Design Principles and Practical Applications - Chapter 9 Generating Randomness - Section 9.4 The Generator

I'm currently reading "Cryptography Engineering - Design Principles and Practical Applications" written by "Niels Ferguson, Bruce Schneier, Tadayoshi Kohno" published by Wiley in ...
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AES CTR: Random IV

I want to use AES CTR with a random IV, as this would be the easiest way for me. I have a cryptographic module, that supports true random number generation. Due to compatibility, I must use AES CTR. ...
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AES256 CTR nonce generation

I am following a wiki diagram for CTR mode of operation in AES256. The documentation states that for it to work you need a random nonce with 8 bytes and then a counter of 8 bytes. So I guess you can ...
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How to correctly implement an archetypal encrypt-then-MAC AES-CTR + HMAC mode cipher?

I've created an AES implementation in Python as a learning experience (mainly for encrypting/decrypting files), and wanted to make sure that I haven't made any huge mistakes in my logic (of course, ...
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With AES-CTR does the block input need to be implemented as nonce || counter?

I am looking at an AES-CTR implementation (WebCrypto) and it takes an initialization parameter count which is an array of 16 bytes. It then asks you to specify <...
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AES CTR - Counter Management

Let ssuppose that we are using AES in CTR mode to encrypt a number of blocks ($x$ bytes each). How is the current used IV (nonce+ctr) synchronized among both communicating entities? I suppose that the ...
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Malleability for varying length message

Given ciphertext for a message encrypted using $AES-CTR$ along with actual, desired message and IV, I need to perform malleability attack on the ciphertext to change the original message from $M$ to $...
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1answer
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Combining CTR and ECB modes to prevent attacks

In Reusing AES-CTR Keys and IVs for File Encryption, the OP was asking about a composite encryption scheme $$C_i = E_K\left(P_i \oplus E_K\left(IV + i\right)\right)$$ which is basically just a CTR ...
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Re-encrypt modified file section with AES-CTR

I am trying to encrypt a file using AES/CTR/NoPadding. The goal is to re-encrypt the new/changed blocks and leave the old ones unchanged then generate a new MAC. My thinking is that when the file ...
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Designing a secure UDP-based communication protocol

SUMMARY UPDATE: I have changed the title of this question from "Using an encrypted packet counter as a counter value in AES-CTR" to "Designing a secure UDP-based communication protocol&...
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Is there any real attack deployed on the CTR mode over history?

The CTR mode, with its CPA security, is one of the malleable block cipher mode of operations. An attacker can simply modify the bits of the ciphertext stream in their advance. This is due to the lack ...
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Disadvantages of AES-CTR?

On paper, it sounds *very* good to me: secure fast (in my tests it's somewhat slower than ECB (but without most of the weaknesses, more on that below) but faster than every other alternative I tested,...
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AES-CTR security if S-boxes substituion is omitted?

I understand why s-boxes are needed in general especially when ECB mode is used(because of using the same key for encryption of other blocks)but I wonder if it's ...
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135 views

Can I use different IVs when encrypting identical plaintexts with identical keys with AES-CTR?

I would like to use AES-CTR to encrypt the same plaintext with the same key more than once (on different machines). I'm wondering whether I should try to use the same IV each time, or whether it's ...
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1answer
79 views

What is encrypted with the key to give the keystream in CTR mode exactly?

I'm learning how CTR mode and there is something I have trouble understanding. If I understood correctly, two components are encrypted with the key, a nonce and a counter concatenated, and it looks ...
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Using AES-CTR as a PRNG

AES-CTR is not considered as a CSPRNG, why ? Is it unsecure to use it when a password is hashed with Argon2id to produce the seed to generate all random data needed for an end-to-end encyption system ...
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Is precomputing AES-CTR key stream secure?

Q0 : Is the precomputed key stream vulnerable to side-channel attacks like a lookup table for exemple ? I don't think it is because a lookup table is accesed very often, that's what makes it non ...
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AES-256 CTR with ESSIV, is this correct?

I am having some problems encrypting disk using AES-256 in CTR mode, with ESSIV iv generation (I am aware of couple of flaws, although this mode is enough for now). What I have here is: ...
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EAX vs CTR vs XTS + cascade ciphers in disk encryption hell

Often when I stumble across something interesting, I lose myself in the most overkill ways of implementing it. Today it was full disk encryption: I'm about to move to QubesOS, and I want to secure my ...
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Which is more secure, AES CTR or OTP with generate key?

My idea of the OTP is to generate from 50 letters (5 words, each 10 letters) a new pad of 2000 random letters, then attach user email to the pad end (to make it unique). The keywords and the pad will ...
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Repeating nonce in CTR mode

Can anybody explain in detail why repeating nonce is dangerous in CTR mode? Two cases to explain When plain text is repeated for each nonce. When plain text is unique for each nonce .
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Behavior of AES-CTR with 128-bit nonce and possible overflow

If I feed 128 bits of randomness into AES-CTR as its IV / nonce / initial counter, what will happen if I feed in a random 128-bit integer that overflows and wraps around? I've written a test for this ...
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Using 0 nonce for AES-256 in CTR mode

My question is: I'm using AES with 256 bits key in CTR mode. Will it be less secure if I use a random key and static zero nonce? key = random; nonce = 0;
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How to encrypt huge amount of data using AES-CTR

As far as I know, AES-CTR depends on nonce. If I will use same key and nonce for encrypting 1 block of data and another - it will be unsecure. So, how can I encrypt a huge block of data (about 1GB) ...
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892 views

Is CTR really equally secure than CBC?

Here is a typical cryptographic situation: A secret key exists that is only known to a sender and a receiver of messages. As it is hard to replace that key, since you either need a secure channel for ...
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Do I need to encrypt the IV?

For example, I'm using AES-CTR. I use fixed (random generated) key and random IV. I know that I have to encrypt key but I don't know about IV. If I will encrypt 1 block of data with fixed key and ...
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What is the maximum number of messages that can be encrypted using the same key for CTR mode?

In the counter mode of encryption, the nonce cannot be used again unless a new block cipher key is chosen. What is the maximum number of messages that can be encrypted using the same key? The maximum ...
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Alternative AES key expansion for CTR based random number generator

Daniel J. Bernstein proposes an alternative to NIST AES-CTR based deterministic random number generator (AES-CTR-DRBG). Instead of a less performant complex construction, he uses an standard AES-CRT ...
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Performance of Counter mode (CTR) with Ciphertext Errors

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about Counter mode (CTR) the authors say that: "As a result, its performance is identical to OFB's ...
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8 bit block cipher in CTR mode for practice - counter is 32 bits

I'm given a very simple 8 bit block cipher in which to encrypt plaintext x with k k one performs $ x \oplus k $. I am given IV = 0101 and a CTR of value CCCCCCCC (36bits). My understanding is that ...

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