Questions tagged [cbc]

Cipher block chaining (CBC) is a method for encrypting large amounts of data with a block cipher that can only encrypt fixed length plaintexts. When used with an unpredictable initialization vector (IV), it is secure against chosen plaintext attacks (CPA-secure).

Filter by
Sorted by
Tagged with
0 votes
1 answer
36 views

AES CBC: When to use new IV

I am trying to figure out when to use a new IV for an AES-CBC communication and whether my approach is safe. Here is a quote from Thomas Pornin from a similar question: So, to sum up: you must choose ...
user avatar
  • 135
0 votes
1 answer
44 views

Alternative to CBC mode encryption?

Given that CBC mode encryption is vulnerable to padding oracle attacks, what is the next best alternative ? a) Include a hash check in the API scheme, validate the hash and then proceed with CBC. If ...
user avatar
1 vote
0 answers
36 views

What would be the consequences of using a IV smaller than the block size in CBC encryption?

Here I use a Threefish kernel module with CBC mode. But there is no hash function that can supply a IV with Threefish block size (1024-bits), so I use a 64-bit random IV inserted in the dm-crypt with ...
user avatar
1 vote
0 answers
54 views

Can I decrypt AES-CBC ciphertext if I have the key without IV? [duplicate]

Can I decrypt ciphertext from AES-CBC encryption, if I have the key and ciphertext only?
user avatar
  • 17
1 vote
2 answers
91 views

AES output lengths are not always a multiple of 16

I have a C# solution that encrypts a bunch of small data chunks using AES. ...
user avatar
2 votes
2 answers
84 views

Is TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 vulnerable to Zombie POODLE/GOLDENDOODLE attacks?

I'm getting mixed reports on this one. I have a web host and multiple SSL scanning tools (including the one run by Qualsys SSL Labs), saying that the cipher suite TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256 ...
user avatar
0 votes
0 answers
36 views

calculate a tag of CBC-MAC

with a block cipher having a 256-bit key and 128-bit block length to MAC a 1024-bit message. How many evaluations of the block cipher will be performed to calculate the tag? [Assume there is no ...
user avatar
  • 13
0 votes
0 answers
68 views

what will be the impact of a 2-bit error in a ciphertext block for decryption if AES is used in ECB, CBC and CTR mode?

So I was reading about 1-bit error propagation for AES mode and how it propagates in various modes. I was wondering how error would propagate in ECB, CBC and CTR modes if it was a 2-bit or a 3-bit ...
user avatar
1 vote
2 answers
146 views

Is it possible to find an AES key given part of the key, the ciphertext, initialization vector and mode of encryption?

The following details are given: Partial Key: ...
user avatar
0 votes
1 answer
50 views

Is it possible to perform CPA attack against CBC changing IV by last ciphertext block?

I was trying to do a simple CPA attack against this scheme, to understand better the concept. Instead of using a new 𝐼𝑉 each time, we decide to use the last block of the previous ciphertext as an ...
user avatar
0 votes
0 answers
24 views

CBC byte flipping attack [duplicate]

I'm learning how CBC works but i don't understand when altering the first 2 bytes of the ciphered text why the 1rst block and ONLY the first 2 bytes of the second block are altered. The first 2 bytes ...
user avatar
2 votes
1 answer
296 views

Can you use RSA in “CBC mode”?

Are there any security concerns with using RSA in “CBC mode”? Specifically: if I use RSA encryption as my block cipher operation, and apply the standard CBC mode operations including a random IV, will ...
user avatar
0 votes
1 answer
58 views

Is multiple encryption using CBC mode of operation susceptible to Meet-in-the-middle attacks?

I read it once on a page (I don't remember the link and I coundn't find it) that said about a cascade of AES with two 256-bits keys and that it provides 384-bits of security. Maybe not 512-bits of ...
user avatar
0 votes
1 answer
70 views

Is CBC mode of encryption still safe as long as it's not use to send messages over a network?

I'm still reading about the Padding Oracle attack and Side Channel attack that can be performed to decrypt cipher text encrypted with CBC though it's still not clear to me. But base on my little ...
user avatar
1 vote
2 answers
104 views

changing messages for authentication without the tag changed. (CBC-MAC)

do you know about CBC-MAC? I have iv ,MAC and Transaction but no key. and I should change Transaction without change cipher text. do you know how this is possible at all? In addition, I do not have ...
user avatar
  • 21
2 votes
2 answers
119 views

Why bother to generate Key, IV and encrypt them?

When we perform encryption with Public or Private Key, Asymmetric AES with RSA and CBC 128, and when we use the padding as well. Why do we have to bother adding the additional: Key + IV? ...
user avatar
2 votes
2 answers
436 views

Distinguishing the correct IV from incorrect IV in AES CBC when key is known

Currently, I'm using a static IV value for all encryption and decryption but I would like it to be dynamic for each encyption/decryption request so I started using new byte[16] and it works. The ...
user avatar
1 vote
1 answer
407 views

Decrypt AES-128-CBC encypted partial RSA Key

I am given a private RSA key, which header indicates that it is AES-128-CBC encypted. Note that the last ten lines of the key are missing. (This is part of an educational task.) ...
user avatar
  • 111
3 votes
1 answer
82 views

Why does CBC-MAC(M) = CFB-MAC(M)?

I don't understand why $\text{CBC-MAC}(M) = \text{CFB-MAC}(M)$. Has it something to do with $\text{CBC-MAC}(M) = C_L$ and $\text{CFB-MAC}(M) = E_K(C'_{L-1})$?
user avatar
1 vote
1 answer
271 views

AES-CBC Hash Function Collision Resistance

I am using AES-CBC as a hash function which is encrypting a block of length n. The blocks, m = (m1, m2, ..., mn). The IV is one block long and the encryption key is length 128, 192 or 256 bits. Will I ...
user avatar
0 votes
1 answer
78 views

Why are des-cbc-hmac and rc4-hmac-exp considered weak in kerberos?

Kerberos uses des-cbc-hmac (mac and encrypt) and rc4-hmac-exp based on md5 (mac and encrypt I think) in their encryptions. Those encryptions are considered as weak and should not be used. Why are they ...
user avatar
  • 175
0 votes
2 answers
94 views

Grover algorithm for AES in CBC mode

Hello, I was wondering whether it is theoretically possible to use Grover alrogithm to break AES in CBC mode. Assume that I have ~1000 plaintext/ciphertext pairs and key length is 128 bits. I thought ...
user avatar
  • 15
1 vote
2 answers
80 views

Integrity while using CBC

We have a body we want to encrypt using CBC, and we add to that body one block of known text to both sides. newBody = body + knownBlock now we encrypt newBody using a key known to both sides, then we ...
user avatar
1 vote
1 answer
85 views

Safety of AES-256/CBC/PKCS#7 + randomization and reusage of IV

As a start, I'm by any means no expert or anything near that in cryptography. I know the very basic about this, enough to more or less choose a method to implement and then read about it so I knew ...
user avatar
  • 113
3 votes
2 answers
122 views

CBC mode with predictable IV ok if key is only used once?

Someone told me recently that using CBC mode with a predictable (e.g. all 0) IV is reasonably secure if a key is only used for encryption one time. I've gone through a couple of examples of chosen ...
user avatar
  • 1,900
1 vote
1 answer
50 views

Why is Masking used in CMAC? [closed]

I am working on masking in CMAC. If masking is not used, then what will be the behavior of CMAC?
user avatar
0 votes
0 answers
52 views

CBC mode, fixed Key and IV but unique plaintexts

My transport channel is sufficiently tiny that I don't want to give up 16 bytes for an IV (AES block size). My environment is also resource constrained such that I have no RNG. I have read over and ...
user avatar
1 vote
0 answers
41 views

Where exactly do you add the zeroes to a URL in a padding oracle attack? Also, how would you decrypt a file this way?

I have been studying various crypto attacks, and one of the attacks that I have recently studied was the padding oracle attack. Now, I mostly understand it, but there is one aspect of the padding ...
user avatar
  • 13
2 votes
2 answers
177 views

Does reusing IV in AES-CBC weaken it?

Rsynccrypto allegedly uses AES-CBC with a twist: If the last few bytes of plaintext meet a condition*, then stop, pad the current block and start encrypting new block from the current position in file ...
user avatar
0 votes
0 answers
65 views

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 ...
user avatar
1 vote
0 answers
64 views

Formal security arguments for 3 round feistal network using PRF

There is a proof sketch in Introduction to modern cryptography that a three-round feistel network using pseudorandom round functions is a secure pseudorandom permutation PRP Πk against probabilistic ...
user avatar
1 vote
1 answer
1k views

Online AES Calculator

I am currently looking into how AES works and found a calculator online: http://testprotect.com/appendix/AEScalc I understand that the AES process has 10 rounds of calculations. Does this mean that ...
user avatar
  • 11
0 votes
1 answer
52 views

Does XORing a random block into a layer of CBC encrypted message add some bit strenght?

Let's suppose I encrypt a message with a block cipher in CBC mode, keep the key and IV secret and XOR a random block of data in each encrypted CBC block, being the XORed block the same for each CBC ...
user avatar
11 votes
2 answers
2k views

Random data CBC padding scheme?

When using AES in CBC mode, padding is required when the last plaintext block has not the length required by the cipher. Let's say $k$ mode bytes would be required to fill the block. My idea was to ...
user avatar
1 vote
1 answer
131 views

Finding IV for forgery of AES CBC-MAC with non-fixed IV

As CBC mode might do several rounds, how it could be possible to find another IV for forgery attack? This is an example from my course: Assume you receive a pair with the plaintext $P_1$ and its MAC ...
user avatar
  • 13
0 votes
1 answer
142 views

AES-128 CBC encryption : ciphertext size seems too large

I am trying to encrypt messages with the AES symmetric algorithm using C language. I am using a key, an Initialization Vector (IV) and a plaintext, all with a length of 16 bytes. I expected as output ...
user avatar
0 votes
1 answer
243 views

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 ...
user avatar
1 vote
0 answers
93 views

Proving Security of a Tweakable Block Cipher in CBC Mode (Threefish)

I want to prove the security of a Tweakable Block Cipher in CBC Mode How does one prove the security of a Tweakable block cipher (ie Threefish) in CBC mode with a random IV and a constant (public) ...
user avatar
  • 31
0 votes
2 answers
1k views

AES/GCM/PKCS5Padding giving issues while AES/CBC/PKCS5Padding works fine for my use case

I have a requirement to read-encypt-save plus its reverse i.e. read-decypt-save files through chunk/block mechanism (single operation not feasible because of huge(GBs) file sizes). So essentially the ...
user avatar
2 votes
1 answer
125 views

How to create the ciphertext that generates a desired plaintext in CBC (previous cipher- and plaintext are known)

I'm struggling with understanding this part of the literature: It can be assumed that the entire ciphertext AND plaintext is known. Considering the encryption method is $C_i = enc_k ( P_i \oplus C_{...
user avatar
1 vote
1 answer
65 views

Exploitability of AES in CBC Mode For Recovery of Plain Text

I'm aware of existing literature that shows in a comprehensive manner just how simple it is to tweak the ciphertext of AES-CBC such that the decrypted message ends up being entirely different than ...
user avatar
  • 115
4 votes
2 answers
218 views

Substitution ciphers amended with cipher block chaining: susceptible to frequency analysis?

I have been studying ways to amend a simple substitution cipher, and one of the toy suggestions was to use CBC in the following way: identify each letter with a number from $0\ldots 25$ start with a ...
user avatar
1 vote
1 answer
1k views

Finding the IV of AES CBC (CTF)

We have a python program that encrypts/decrypts plaintext given in hex to a cipher using AES CBC. We know that the IV is the same and is not going to change (it is stored in a file). How can we ...
user avatar
  • 17
1 vote
1 answer
108 views

Is it safe to reuse an IV 100 times to a single key with AES CBC? [duplicate]

I have a unique 6 digit number that I am generating a IV from. I am trying to make it as unique as possible. From my programming, I am able to get it down to only have 100 duplicate IVs per unique 6 ...
user avatar
0 votes
1 answer
111 views

Which encryption technique should be adopted to keep the search functionalities?

I am in exactly the same situation as described in this post. I must be able to encrypt data from a client workstation then send it to an untrusted server (encrypted at rest), then decrypt it only on ...
user avatar
3 votes
2 answers
682 views

AES-CBC decrypts to wrong output?

Someone I know showed this to me, and I can't put a finger to why it's happening. Am I missing something? They encrypt the text, and the output is really guessable. $u\to t$, $i\to h$ (it's one letter ...
user avatar
  • 33
2 votes
0 answers
221 views

An exercise to show that CBC Chain is insecure

The CBC-Chain mode of operation is a CBC variant in which the IV that is used for the very first message to be encrypted is randomly selected, whereas the IV used for each subsequent encrypted message ...
user avatar
0 votes
0 answers
182 views

Is it more secure to use Diffie-Hellman to generate a symmetric AES key for use with CBC, rather than use CBC directly atop RSA encryption?

Short question: If we assume a one-session use public RSA keypair on both sides, and if we assume that the input stream will be split into blocks -- with CBC encryption -- is there any security ...
user avatar
  • 113
0 votes
0 answers
295 views

Is ECB mode more suitable than CBC mode while encrypting a long bit string?

I know that ECB is less secure than CBC, but will it be suitable for encrypting a long bit string?
user avatar
1 vote
0 answers
28 views

Is it necessary to use an IV in CBC mode when just encrypting one file? [duplicate]

As far as I know, CBC mode, even with a null IV, will encrypt identical plaintext blocks to unique ciphertext blocks within a single file. The purpose of an IV is to obscure the similarities between ...
user avatar
  • 11

1
2 3 4 5
10