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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Quadruple DES vs AES-128 security

I came across this question regarding the security of Quadruple DES (hypothetically DES done four times) in CBC encryption mode vs security of AES-128 in CBC encryption mode. What parameters help to ...
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7zip : Why does encrypting the same file with AES-256 not give the same output?

Using 7-zip 19.00, on Windows 10 1909, build 18363.592, I encrypted a text file with the contents "hello there" using AES-256 and the password "123". I did this two times, the exact same procedure, ...
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Multiple IV CBC

CBC's encryption is not paralelizable but I could divide a 64 block message in 4 16 block parts and encrypt those 4 parts separatly in parallel using a diferent IV for each one. Is this unsecure ? Is ...
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How can Cipher Block Chaining (CBC) in SSL be attacked?

I am trying to understand how CBC-mode in SSL/TLS can be attacked. I have been looking around online but all examples and explanations are very hard to understand and follow. Can you give a simple ...
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AES-256, CBC, plaintext length is multiple of block size: Does PKCS #7 padding weaken the encryption?

Of course, padding is superfluous when AES with CBC is used if you know that the plaintext length is a multiple of the block size. But does the padding precipitate a weakness in the encryption? ...
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Looking for a way to enlarge a message so that any modification to the “enlarged” message makes recovering the original message impossible

Let's say we have a message m of small size. I am looking for a system $S$ so that $S(m)$ is arbitrarily large, we can easily compute the inverse $I(S(m)) = m$, and any modification to $S(m)$ makes it ...
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Alter plaintext through IV in block cipher AES in CBC mode

IV: 69bb375aa919c72aa561dd7b7ffacf66 Ciphertext: "c28ea025d10186510855d083747d6435c808d9857075abd9bfc54b094e60eaf3" Plaintext: "SEND ENCRYPTED DATA" I want to be able to change the resulting ...
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Is it okay to have no IV when using AES-CBC with unique keys, that are however derived from one shared key?

Given $\operatorname{AES-CBC}$ (128-bit), with $IV=0$ and unique encryption keys $$K_{Enc} = \operatorname{CMAC}(MK, \text{known_text})$$ where $MK$ is a shared symmetric 128-bit key and $\text{...
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Crypto system design : How to design Encryption for Zero width characters

Zero width character's can be used to hide text in plain sight.I am building a system where user's can provide their secret message , cover message and a password (key) which I would encrypt and give ...
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OPA attack with IV || ciphertext1 || ciphertext2

I know this is a kind of a very un-specific question. But I cannot figure it out where I am doing it wrong implementing an Oracle Padding attack. So What I'm supposed to do is to send a iv || ...
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Should I use ECB or CBC encryption mode for my block cipher?

Can someone tell me which mode out of ECB and CBC is better, and how to decide which mode to use? Are there any other modes which are better?
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Does AES-CBC always use PKCS#7?

I need to add AES decryption with a 256 bit key to our software, and of course I won't do it myself; rather, I chose a library that works fine for our needs. It supports various modes of operation, ...
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How do I find out whether a message in CBC has padding?

When a program is decrypting a message encrypted by CBC mode, what does it find out, whether the last bytes of the last block is part of the padding or part of the plaintext? Example: Use CBC mode ...
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Encryption & decryption in AES CBC mode - Which is faster?

I wrote a small code to compute the time consumption by the AES in CBC mode, I noticed that the encryption is faster than the decryption, my question: Is my result correct? If yes, why is the ...
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DES-CBC with random IV - how big is the keyspace? Can COTS tools crack it?

I've spent the night reversing the implementation of the 'Basic Text Encryptor' from Jasypt [1]. The algorithm is defined in documentation as 'PBEWithMD5AndDES'. The implementation is this: A ...
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CBC encryption + CBC MAC reusing key in MAC-then-Encrypt

I'm reading the Handbook of Applied Cryptography by ‎Alfred J. Menezes et al. Especially, I'm stuck with the case that reusing key for CBC encryption and CBC-MAC in MAC-then-encrypt structure. My ...
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What is the difference between CBC and GCM mode?

I am trying to learn more about GCM mode and how it differs between CBC. I already know that GCM provides a MAC which is used for message authentication. From what I have read, and from the code ...
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Weakness in a CBC-like XOR cipher

A simple symmetric encryption algorithm can be written as follows: Input message M and 64 bit key $K$ Divide M into 64 bit size blocks $B_1...B_n$ Get first block $B_1$ and perform bit-wise $\oplus$ ...
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How are initialization vectors used in TLS 1.1?

From my understanding, TLS 1.0 can use CBC to encrypt data. To do so, it creates one initialization vector (IV), and then uses the previous ciphertext block as the IV for the next record. I made this ...
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Randomly initialised global counter used to encrypt the kth message with IV = IV + k mod 2^n

The use of an increasing IV is not secure for a block cipher. That is, using a random IV for the first message then IV + 1 for the second , IV + 2 for the 3rd etc. How can I construct an attack to ...
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Is there any way to find out two numbers such that the XOR between them is a given number?

I have the following operation I took from a cryptanalysis I'm performing for a specific CBC encryption where the challenger has provided the key: ...
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Can CBC ciphertext be decrypted if the key is known, but the IV not?

Let's say that there is a binary file encrypted with AES in CBC mode (i.e. using a key and initialization vector). If key is known, but IV is not, is it easy to fully decrypt the file? How hard is it?...
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Why is CBC with predictable IV considered insecure against chosen-plaintext attack?

I just learned that using CBC encryption with an IV which is predictable is not secure. From what I understand, using certain plain texts, and then guessing the IV that it uses, the attacker can ...
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Validating successful decryption in AES

I have a program which uses AES-256 in CBC mode to encrypt and decrypt files. As I have quickly realized, AES will even use an incorrect passphrase to decrypt data, which leaves me with no way to ...
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When using CBC-ESSIV for disk encryption, why does the generation of IV require a hash then encryption instead of only one hash?

The CBC-ESSIV algorithm specifies how to calculate the IV to use for a given key (K) and sector number (S) as the following: $$\text{IV} = \operatorname{Enc}(\operatorname{Hash}(K) , S)$$ https://en....
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Is CBC really dead?

I developed a p2p-app in C# which sends and receives encrypted text messages (50kB). For encryption, my app uses 128-bit AES in CBC cipher mode. For each message it uses a new randomly-generated IV. ...
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Block cipher linearity (in relation to hill ciphers)

So while I knew hill ciphers were a form of block cipher (I'm assuming all the ones I have solved to date were ECB or something similar), so that got me thinking. Is it possible to use hill ciphers in ...
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Another cut-and-paste attack on CBC mode

I am trying to see specific cases of attacks in the CBC mode, in particular, I am investigating some attacks such as Example of a cut-and-paste attack on CBC. Here I have posted something similar and ...
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AES-128-CBC padding size [closed]

I'm trying to figure out how padding works by seeing what happens when I try to encrypt a 16 byte file with AES-128-CBC. My understanding was if I encrypt a file of size, say, 28, then there would ...
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How to break CBC cipher with partly known plaintext?

I'm learning some IT security and during practice I found an exercise I couldn't solve. I have an encrypted message with block cipher in CBC mode. The blocks are one byte long and the first block is ...
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CMAC Generation : If input payload length is not aligned in 16 bytes, what are the possible side effects?

While searching for answers ,I understand that RFC AES-CMAC 4493 is suggested by NIST to overcome if payload is not aligned in 16 bytes. I would like to know what drawbacks/insecure caused by AES-...
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TDES (Triple DES) DUKPT decryption

We have a POS (Ingenico) that uses DES3-CBC encryption using a derived key. It sends encrypted data, and 10 bytes size Key Serial Number (KSN). I tried to use ...
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Cipher Block chaining but with encrypting the plain text first then xor with IV

I have just learned about the CBC mode of operation and that it gives the cipher by xoring the plaintext m0 with random IV and then encrypt it with random key and I found out that the CBC is not CPA-...
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Longer IV generation from a single block IV for ICBC

I was reading a question about ICBC here and it mentioned that you would need a $s \cdot n$-bit $IV$ if you would use $s$ "stripes", where $n$ is the blocksize. Say that we don't like transmit that ...
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Why is it difficult to encrypt large amounts of information using quantum key distribution?

An article last month claimed that Toshiba Corp. and Tohoku University recently broke the record for the amount of data encrypted using quantum key distribution by transmitting "a few hundred ...
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Reusing IV but still generating different code?

I'm in a beginner's cryptography class and I'm trying to figure out if I'm doing something wrong, or if I just don't understand why something is the way it is. I created a simple .txt file of 124 ...
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Example of a cut-and-paste attack on CBC

I am reading the cryptography book by Stamp and there is a cut-and-paste attack on $ECB$ and this is easy to follow because $ECB$ is relatively simple, the problem is that I would like to see an ...
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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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Parallelizabilty and prepocessing in Modes of operation (with example)

I have a doubt about parallelizability and preprocessing in modes of operation. I understand that these two technologies are able just when the "block" is independent. In another way, ad example in ...
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AES CBC Security

I am building an Apache webserver with TLS 1.2 and OpenSSL 1.0.1. So far, I have enabled 2 encryption algorithms - ECDHE AES-256 GCM and ECHDE AES-128 GCM. Firefox and Chrome / Chromium use NSS which ...
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AES-128 Decryption in Objective-C just slightly off [closed]

I have been asked to integrate a home-grown CRM system with a 3rd-party data service provider (DSP). The DSP has encrypted the information they are providing. I only have their decryption ...
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During padding oracle attack (CBC), how is first byte of plaintext block is obtained?

Imagine conducting a padding oracle attack against CBC mode with 16-byte length blocks, and PKCS#5 used for padding. You start, as always, revealing the last byte of plaintext. Then you iteratively ...
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What are easy yet fool proof ways of ensuring that AES encryption algorithm works like it should and no bugs/developer mistakes have sneaked in?

As a developer when it comes to encryption, there is an insane amount of weakness/mistakes/bugs that the programmer can add to the encryption algorithm. So a pretty general question to the crypto pro’...
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AES CBC in need of multiple IV's, possible to avoid creating duplicate iv's by using resulting cipher text 16 bytes as next iv?

I saw a little close to these questions but not exactly. Encryption method AES-256-Rijndael-CBC: if we have multiple cipher chunks that look like this: {iv}{cipheredchunk}{chiphered chunk}{chiphered ...
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What is the advantage of XTS over CBC mode (with diffuser)?

I have some problems in understanding the "advantage" of AES-XTS compared to CBC with diffuser. I read something about FileVault, in this paper they mention the two modes of operations XTS and CBC (...
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Given the key, the plain text and the cipher text can I calculate the IV used in CBC mode?

If I have the plain text, the ciphertext and the key for an AES-128 CBC operation, can I determine the IV, even if I don't know the padding (assuming the padding follows one of the more common formats)...
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How does AEAD guarantee authenticated encryption and plain AES does not?

This is a follow up to my earlier question. This is more out of curiosity in how AEAD (like CCM or GCM) works compared to encryption in other modes (like CBC or ECB). Suppose you have AES-256-CBC ...
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Error propagation in CBC [duplicate]

I am doing an error propagation experiment with the CBC mode.I have encrypted a 100 byte text file with openssl. I made the 55th bytes of my encrypted file corrupted.As per theory the corresponding ...
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1answer
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128 bit AES CBC bit flipping on second block

I have a 128 bit AES cipher in CBC Mode with the IV prepended to the message. I am aware of the security issues here, but that is exactly the point of my example. I would like to change the plain text ...
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AES 256 CBC - Storing local data, how to save IV vector?

I want to use AES256 CBC for protecting small data (<100kb) against misusage for my application in the local store folder. I'm not an expert at data encrypting so I'm to try to understand it step ...

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