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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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Why is the ciphertext output 32 bytes long when i encrypt a 16 bytes long plaintext by using AES-128-CBC

I am studying AES algorithm, as far as I know, encrypting a 16 bytes plaintext will result in a 16 bytes ciphertext. But I got a different result when trying to encrypt a 16 bytes plaintext using AES-...
user25513320's user avatar
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Producing existential forgery against CBC-MAC

Given the above MAC scheme, I want to ask how to form existential forgery of this scheme? I have looked through a couple explanations on existential forgery but still struggle understanding the ...
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crack AES CBC with chosen Ciphertext, IV and known plaintext [closed]

I am currently tackling a challenge involving AES CBC encryption where i have the ability to choose both the IV and the ciphertext, and then provide it to a service. The service decrypts with an ...
ucker's user avatar
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Security of modified CBC$ mode encryption

I am trying to understand the (IND-CPA or lack thereof) security of a modified CBC mode. Instead of choosing the IV completely at random per plaintext, the adversary provides a "pre-IV" ...
puppet puppet's user avatar
3 votes
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Understanding CBC-MAC Algorithm and Nested Encryption

In the CBC-MAC algorithm as given in the image below, I have two questions: It is said that the CBC-MAC is simply the last block of ciphertext if the message is encrypted using CBC block cipher mode, ...
revision's user avatar
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Does truncating a CBC ciphertext result in a truncated plaintext?

I want to know why in the CBC cipher, if we truncate the first block in the ciphertext then the corresponding plaintext block is truncated in the same way. I have an equation for the plaintext $m_i$ ...
revision's user avatar
1 vote
1 answer
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Statistical differences between ciphertexts generated by AES in ECB vs CBC mode?

Given two ciphertexts encrypting the same (natural language) plaintext, where we know that one of the ciphertexts was encrypted with AES-CBC (and unknown IV) and one was encrypted with AES in EBC mode,...
mudskipper's user avatar
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Putty PPK Encryption Questions (or AES-CBC)

I am learning about aes-cbc and to simplify things we need two parameters for encryption and randomness (key and IV). IV is random at runtime and will be used to randomize the first cipherblock which ...
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Using AES-CBC with a random number plus a counter for the IV

I understand that AES-CBC uses the following scheme for encrypting data (diagram from Wikipedia): And, I understand that we don't want initialization vectors to be predictable or constant, and also ...
Jojodmo's user avatar
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Given and encrypted message, is it theoretically possible to decrypt a message without the key or guessing it? If so, what methods could be used?

Decrypting an AES-Encrypted Message Without the Key: A Cryptographic Challenge Summary: I am investigating the possibility of decrypting an AES-encrypted message when the encryption key is unknown ...
NeoX's user avatar
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2 answers
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Rate the security of the following MAC

Ok we know when we add a random IV in our "modified encrypted" MAC became useless and the IV can be forgery, then our encryption scheme becomes vulnerable to chosen plaintext attacks. ...
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CBC KEY recovery when KEY=IV

We have access to an encryption and decryption server with the following implementation. How can we get the secret key by interacting with this server? ...
Sahar's user avatar
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0 answers
157 views

CBC Predictable IV Help

I have this problem where I need to guess if bob wrote "yes" or "no" It is using AES-128-CBC and it tells me the next IV to be used. it takes input as a hex string and does the ...
drift's user avatar
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1 vote
1 answer
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Is the Bit Flipping attack on CBC mode possible if the IV is not know to the attacker?

This is a follow up question to: Bit Flipping Attack on CBC Mode which demonstrates that a bit flipping attack with a known IV is possible on CBC mode. Is it safe to assume that the bit flicking ...
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Does using a block cipher in CBC mode *twice* result in an all-or-nothing transform (AONT)?

Use a block cipher in CBC mode with a public or all-0 key. Twice. Wrapping the last block into (xor) the first on the second round. Every block will depend on all previous and all successive blocks. ...
Arnold Snooli's user avatar
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how 0/n split prevent BEAST attack against TLS?

I read that to mitigrate BEAST attack openSSL tried to inject empty TLS record before each real TLS record. and by doing that there is no opportunity to execute an attack but i dont understand way? ...
eitan's user avatar
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How to get the rest of 10 bytes (from total 32 bytes plaintext) of plaintext from a 48 byte ciphertext using AES-128 when knowing 22B of plaintext?

I have a challenge in which I need to decrypt 32(?) bytes of plaintext, which by encryption resulted in 48 (this for sure) bytes of data. It's a black box challenge, but managed to figure out the ...
Sir Muffington's user avatar
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Key expansion in AES CTR mode

While working with AES 256 in CBC mode, I learned that it requires Key Expansion - forward (for encryption) and reverse (for decryption). Does AES CTR mode also requires such a step ? Or can the 256 ...
shaiko's user avatar
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AES CBC - Find IV (CTF)

I am currently trying to solve a training challenge based on AES with CBC. This is the infos I'm given: ...
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Is it possible to craft a valid AES-CBC cipher-text that will decrypt (to random) with any possible key?

I am mainly looking to perform this trick for fun. I have access to an API that uses WebCrypto under the hood for encrypt and ...
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CBC not CCA secure

I always get stuck at those kind of exercises in my Cryptography class. I just don't understand how should I build these scenarios of "sending m1 and m2 and then somehow telling if it was m1 or ...
trying_to_learn's user avatar
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Padding Oracle Attack Example

I try to understand a oracle Padding Oracle Attack example. I try to solve this question but I didn't figure out the answer. A 7-byte message is padded per PKCS#5 and encrypted using the CBC mode of ...
MariaDb's user avatar
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1 answer
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Cryptography particular block length valid message

I am new at cryptography and start to learn some terms. I just saw an question in the book and didn't got a clue about this question. Could someone can explain me the answer of this question? Because ...
MariaDb's user avatar
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Padding Oracle Attack - Decrypting First Block with Static IV

I'm trying to understand the exploitability of the padding oracle attack, which enables someone to decrypt and encrypt the contents without knowing the encryption key. Can encrypted data with the ...
VitoCorleone's user avatar
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Exploit 3DES-CBC with known checksum of plaintext and repeated IV

I came across the following enterprise encryption scheme. I laughed when I first saw it, but I'm not a specialist and I'd like to know how bad it really is. 3DES-CBC k1=k2=k3 for 3DES IV for CBC is ...
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Role of IV in Perl's Crypt::Rijndael

Sorry in advance if I'm asking a stupid question: I thought the role of "IV" in encryption is to avoid having identical ciphertext for identical plaintext. So one could use some random IV. ...
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1 answer
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GCM-SIV vs CBC with fixed IV?

I keep hearing CBC with fixed IV mode is bad because it has similar issues to the codebook breakdown of ECB mode. However, people seem quite willing to recommend AES-GCM-SIV for deterministic ...
Paul's user avatar
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1 answer
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How to encrypt with CBC, step by step?

I have this message "Hello from another world" Can you explain how to encrypt it with CBC step by step? Are the message characters ...
Edward Akina's user avatar
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1 answer
437 views

How is DES used with CBC?

I'm reading our school's notes for cryptography, and it does a good job explaining CBC and DES in detail, but it fails to provide good information on how they are related. From what I've researched so ...
Green Ideology's user avatar
6 votes
2 answers
1k views

Always set the IV to 0 randomized CBC

Please explain what goes wrong if we always set the IV to 0 in randomized CBC, and use the system to encrypt two different messages m0 /= m1 with the same key k. I ...
Amirhossein's user avatar
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169 views

AES-CBC collision resistance of hash function [closed]

I'm very new to cryptography and am having some issues with the following question ...
George's user avatar
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AES-CBC-MAC forgery attack

I have a CBC-MAC scheme using AES as the block cipher (T=H_K1(M)), which gives me a tag and a stream cipher using another key and a nonce, which gives me a cryptotext (C=E_K2(N,M)). So my question is ...
MSCHA's user avatar
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1 vote
1 answer
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Is it normal that cypertext size can be smaller than IV when using AES-256-GCM?

I noticed that when using AES-256-CBC with a 128-bit IV, the ciphertext is always at least 16 bytes long (size of IV). I also noticed that when using AES-256-GCM with a 96-bit IV, the ciphertext size ...
sunknudsen's user avatar
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CBC Operation with Known IV [duplicate]

I am trying to understand how XOR operation can lead us to know the plaintext if we can predict the iv using the chosen plaintext attack game.
CryptoGuru's user avatar
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1 answer
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CBC-MAC Forge Attack Question

I am trying to understand how the forgery attack works when using the CBC-MAC Algorithm
CryptoGuru's user avatar
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302 views

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 <...
Eddy's user avatar
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2 votes
1 answer
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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 ...
mike.w's user avatar
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1 answer
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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 ...
sunknudsen's user avatar
3 votes
3 answers
6k views

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 ...
tarun14110's user avatar
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0 answers
121 views

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 ...
sunknudsen's user avatar
7 votes
3 answers
6k views

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 ...
Erwin's user avatar
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1 vote
1 answer
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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 ...
Grub's user avatar
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2 votes
2 answers
730 views

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 ...
veda-s4dhak's user avatar
3 votes
2 answers
448 views

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 ...
Ravindra HV's user avatar
2 votes
2 answers
341 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 ...
earthling's user avatar
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1 answer
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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 ...
Ravindra HV's user avatar
1 vote
0 answers
84 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 ...
phantomcraft's user avatar
1 vote
0 answers
61 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?
Yara's user avatar
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2 votes
2 answers
2k 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. ...
Barak Gall's user avatar
2 votes
2 answers
927 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 ...
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