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).

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Decryption failure for NIST vector AES-CBC-128

I am learning/exploring the openssl library for encrypting and decrypting data while encryption goes through fine I see standalone decryption not working as I expected. The test vector I am using is <...
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what is IV predictable?

What is IV predictable in the CBC mode? We only need one IV once for CBC mode, does the IV-predictable means we know the initialization vector before we start a CBC mode? Or it means we know each ...
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Can one infer concatenated ciphertext block boundaries through digital forensics?

Say one encrypts multiple plain text blocks with same IV but different keys using AES-256-CBC, can one infer concatenated ciphertext block boundaries through digital forensics? Example Plain text ...
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Is there a security risk to use AES-CBC as stream cipher?

I am building a chat application where I want to encrypt each character while they are typing. I would require a stream cipher for that. I am planning to use AES-CBC mode with HMAC. Are there any ...
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Is AES-256-CBC secure in the context of offline encrypted backups?

My understanding is that AES-256-GCM is more secure given it supports authentication. Also, my understanding is that AES-256-CBC is vulnerable to “chosen-plaintext”, “chosen-ciphertext” and “padding ...
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Can one securely use same salt and IV with different KDF-derived keys when using aes-256-cbc?

I know this is theoretically bad practice, but please bear with me… Assuming following spec: Salt and IV are randomly generated using cryptographically-secure RNG. Argon2 is used as KDF so ...
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What is DES-EDE3-CBC?

I came across DES-EDE3-CBC and a quick search didn't yield a clear explanation of what it is. Clearly, DES is the Data Encryption Standard and CBC is the Cipher Block Chaining mode. EDE is probably ...
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How does a GMAC in GCM not nullify the utility of a seekable decrypt-able stream

I have been looking at the Galois/Counter Mode (GCM) for stream encryption. I understand the idea that it's a stream cipher and so it can be encrypted one bit at a time by XORing with the key stream ...
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What AES mode does the CMAC use in Secure Channel Protocol 3 (SCP03)?

I am looking to verify a card cryptogram sent from a smart card chip in accordance with SCP03. According to the SCP03 spec, the CMAC is used to generate a MAC to authenticate messages sent to/from the ...
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Is disabling padding integrity check in CBC implementations a good way of overcoming / mitigating padding oracle attack?

Given that CBC mode has a padding oracle attack, would disabling the padding integrity check be a good way of overcoming the vulnerability (this may result in frustration among existing users with ...
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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 ...
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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 ...
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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 ...
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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?
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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. ...
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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 ...
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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 ...
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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 ...
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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: ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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? ...
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2 votes
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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 ...
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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.) ...
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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 $\text{CFB-MAC}(M) = E_K(C'_{L-1})$?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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?
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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 ...
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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 ...
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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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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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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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) ...
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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 ...
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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_{...
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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 ...
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