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

learn more… | top users | synonyms

1
vote
1answer
76 views

Difference between plain AES CTR and “CCM-style” CTR

I am trying to adapt the following function from SJCL, which does "AES-CCM" style CTR encryption, to do "pure CTR" encryption. I am playing around with SIV and would rather use this well-reviewed ...
0
votes
1answer
50 views

Multi cipher CTR

What is your opinion on this scheme: 1)get IV from CSPRNG 2)set 3 encryption keys k1,k2,k3 (3*key_lenght) (KDF/PBKDF) 3)Use 3 ciphers in CTR mode like this: The initial IV is encrypted using ...
5
votes
2answers
165 views

Reusing AES-CTR Keys and IVs for File Encryption

I’m implementing some file encryption module with random-access capability and AES-CTR seems the right way to go. I understand that reusing Keys and IVs can expose the file to ‘Stream Cipher Attacks’ ...
3
votes
2answers
124 views

Why does CTR mode XOR the plaintext into the output of the block cipher rather than XORing the plaintext into the input of the block cipher?

As I understand it, CTR mode essentially turns a block cipher into a stream cipher like so: ...
7
votes
2answers
258 views

Why do we use XTS over CTR for disk encryption?

I'm taking Prof. Boneh's crypto class from Coursera, and am unsure on the requirement for XTS mode for disk encryption. It seems that CTR mode would do exactly what XTS can do, but is simpler to ...
0
votes
0answers
57 views

Decryption returns different data

I am new to cryptography so forgive me if I am doing anything stupid. I am following the Cryptography in JAVA book. I am creating my own kerberos. I am stuck at a point. I have Message class which ...
0
votes
2answers
166 views

Game traffic encryption AES CTR + HMAC

I was asked to implement traffic encryption between the game server and clients. Currently, the traffic is not encrypted in any way, which lets players use cheats to listen to the traffic in order to ...
2
votes
1answer
159 views

How does the IV or initial counter increase internally for each block in AES CTR mode?

I am working on Intel AES-NI library and since the AES function is coded using low-level assembly instructions. I could not see how the IV or initial counter increases in CTR mode. In general, how ...
2
votes
1answer
263 views

How good is using AES CTR mode with initial counter as 0?

Is it advisable to use AES CTR mode with the counter initialized to 0? How good is it in security terms?
5
votes
0answers
305 views

What is wrong with AES-CTR-HMAC-SHA256 - or why is it not in TLS?

It seems the only specified CTR mode ciphers in TLS are all GCM based. GCM ciphers run AES-CTR and do authenticated encryption with a MAC based on Galois-field ...
3
votes
2answers
210 views

Making counter (CTR) mode robust against application state loss

Counter (CTR) mode, which is a block cipher mode of operation, has some desirable qualities (no padding, parallel encryption and decryption), but at the cost of failing badly when non-unique counter ...
1
vote
1answer
384 views

Reusing keys with AES-CBC

I heard that key/IV pairs must not be reused in AES-CTR, or when using any stream cipher for that matter. Yet the attacks described do not seem to apply to AES-CBC. Is reusing the same key several ...
3
votes
0answers
113 views

Which encryption method supports random reads?

I have a file containing 16-bit samples and I want to encrypt it, but the problem is that I need to be able to read any random 16-bit value from the file, and be to able to decrypt it, without reading ...
1
vote
0answers
38 views

one-time key, zero IV in stream cipher (e.g. AES-CTR) [duplicate]

Say I am using a random key to construct a stream cipher with, say, AES in CTR mode, which will never be used to encrypt more than one data stream. Is there any advantage, no matter how small, to ...
4
votes
2answers
190 views

CTR mode nonce with aggressive key rotation policy

I'm writing a small encryption library which will be required to use the shortest possible amount of overhead for describing ciphertexts. I want to use CTR mode with a 6-byte random nonce. Normally ...
3
votes
1answer
176 views

AES-CTR with ephemeral keys vs IV

Let's say that we have a key exchange of some sort, which leaves A and B sharing the long-term secret $S$. Then, A and B want to use AES-CTR for the communication, which leaves us with several ...
0
votes
2answers
199 views

Recommended authenticated stream cipher for minimum overhead?

I'm running my TCP/IP protocol secured by encrypting each packet with AES128/CBC, bundling a SHA256 HMAC over that packet. This causes quite a bit of space overhead for small packets, so at first I ...
3
votes
1answer
221 views

Counter Mode: static IV but different keys [duplicate]

Given we are using AES counter mode, suppose we randomly generate several keys, all of them are using same IV (say, zeros). Does this lead to any security issue? I know that in CTR mode, same key-iv ...
1
vote
1answer
309 views

Proper uses for CTR and CBC AES block cipher modes

Assuming the following: Key is randomly generated is being used (32 bytes+) IV is also randomly generated Crypto random key generator is used Data being encrypted contains common bytes like ...
2
votes
2answers
2k views

AES+CTR+HMAC Encryption and Authentication on an Arduino

In my project we would like to encrypt and authenticate the the communication channel between our server and our Arduino nodes, which relies on an underlying TCP channel. We have chosen AES in CTR ...
1
vote
2answers
198 views

Why nobody considers counter re-keying as a standard Block Cipher Mode?

One of the simplest possible cipher modes is setting each successive key as a function F of the previous one. ...
3
votes
2answers
751 views

AES-CTR vulnerability to cryptographic oracle

I am new to cryptographic issues and from what I googled so far I could not retrieve the information I need. Consider the use of AES-128 in CTR mode. Let M be the set of possible plaintexts, for ...
3
votes
1answer
4k views

AES CBC mode or AES CTR mode recommended?

what's benefits and disadvantages of CBC vs CTR ? which one is more secure ?
5
votes
1answer
249 views

Why doesn't CTR mode require blocking?

I've been reading a bit about block cipher modes and I have a relatively straightforward question regarding CTR. In essence, I was hoping you guys would be kind enough to validate my understanding of ...
2
votes
1answer
157 views

How many different keystreams can I produce with AES in Counter Mode?

I'm using a 64-bit nonce (incremented between the streams) and a 64-bit counter (incremented within a stream) for AES in CTR mode. How many different key streams can I produce with this setup?
1
vote
1answer
2k views

Counter Mode in Advanced Encryption Standard(AES) Algorithm

In Advanced Encryption Standard, if I used "Counter Mode", how should I handle the nonce? Should I divide the nonce value into two? For example: I have 128-bit of nonce, should I divide it so I get ...
2
votes
1answer
812 views

Why must IV/key-pairs not be reused in CTR mode?

Many sources mention that IVs must not be reused with the same key in CTR mode, for encrypting 2 different pieces of data, because that totally destroys security - but I haven't found an explanation ...
6
votes
1answer
843 views

Deterministic nonces in CTR mode

I want to encrypt a file with AES in CTR mode. I have a 256 bit master key and the file. Given these, the encryption must be deterministic, so I can't use a random nonce in the usual way. Fortunately ...
5
votes
3answers
3k views

Which one of the Block Cipher modes is the best?

I have two questions regarding the Block Cipher Modes: Which one of the modes is considered the best? I know CBC has a problem of IV since the next block of the plain text is XORed with the result ...
5
votes
4answers
858 views

Is SHA-256 secure as a CTR block cipher?

Generate a 256-bit random nonce. XOR it with a 256-bit reusable symmetric key. This is x. We represent numbers in simple binary instead of a counting function. ...
4
votes
2answers
268 views

Is it safe to store initial counter value for AES-CTR alongside with ciphertext?

The initial counter value can actually be thought of as a sort of IV, which I assume is safe to transmit with the ciphertext, but I really want to be sure that this is indeed safe.