Questions tagged [modes-of-operation]

ways of applying a block cipher to multi-block messages and enabling repeated use without changing the key.

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How is the keystream actually generated in AES CTR

I've been trying to find out how the keystream in AES-CTR is generated, but I can't actually figure it out. Wikipedia and any other sites that "explain" it just say the nonce is padded with the ...
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How to generate a 128 bit IV from a 32 bit value for AES-128 OFB

I have no clue how to determine suitable 128 bit IV (initialization vector) from a 32 bit IV. Encryption AES-128 OFB. The 32 bit IV has value 0x9a23773c (...
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40 views

Performance of Counter mode (CTR) with Ciphertext Errors

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about Counter mode (CTR) the authors say that: "As a result, its performance is identical to OFB's ...
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OFB mode vs LFSR

In the "Introduction to Cryptography: With Coding Theory" by Trappe and Washington, in the chapter about OFB (Output Feedback) mode the authors say that: The OFB mode produces a bit stream and it ...
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Perfect Forward Secrecy Stream Cipher based on Block Cipher

I'm thinking about ways to encrypt an endless stream of data (e.g. a video or audio feed) in a way, where a compromise of the current internal state of the encryption (e.g. a RAM dump) does not ...
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Why is ECB+CTR not a thing?

AES-CTR is nice for its parallelizability and simplicity but if you duplicate an IV you reveal plaintext. Chaining modes like CFB and CBC don't have that problem per se but they are not ...
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Why weak modes of operations are not banned?

If some modes of operations of AES are not secure (like ECB or CBC), which are prone to bit flipping / manipulation attacks, and why they haven't they been banned or advised against by NIST for other ...
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107 views

Which is the best AES mode of operation? [closed]

Is there any reason to choose, say ECB over CBC? Or GCM over AEX? Or CTR over CFB? Is there a best AES mode of operation? And, when required, which is the best padding to use?
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Nonce-misuse-resistance scheme applied after the fact to AES-GCM for defense in depth?

This is a follow-up to a previous question about encrypting IV/MAC results from AEAD ciphers. I have a system I'm working on that needs to use standard (NIST/FIPS) cryptography, at least for its ...
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AES encryption question

If we consider the generation of keys as $$\begin{aligned} K_0 &= E_K(IV); \\ K_{i+1} &= E_{K_i}(A) \end{aligned}$$ Where A is a block of zeroes, and the ciphertext blocks are computed as ...
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Using a non-secure random generator for IV or salt generation

I was just looking at a post on Code Review when I noticed the other answer to the post. While I would agree mostly with the answer, I do however doubt if having a Cryptographically Secure PRNG is ...
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225 views

64 bit clock cipher with CFB mode. One-byte defected from ciphertext. What is the number of bits defected from plaintext

I have a question from an exam; We encrypted a message of size 100 Bytes with CFB. In the transmission, byte number 12 got defected. How many bits defected will be in the decryption. The answer is 72 ...
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Terminology: Is a block cipher in counter mode still considered a block cipher or is it classified as a stream cipher?

I'm confused about what terminology to use. I see people referring to such a cipher-MOO combination using both terms.
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Does there exist a mode of operation that forces mac-then-decrypt?

Alice sends Bob a message using AES-GCM. Bob is a software developer with just enough cryptography knowledge to be dangerous. He wants to start processing data as soon as he receives it. He observes ...
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387 views

What's the best block cipher mode of operation for RSA?

I know that you should never use RSA with any block cipher mode of operation, but theoretically, what's the best block cipher mode (safest) we can use with RSA encryption - without adding any kind of ...
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Lightweight block ciphers that support decryption with minimal overhead?

Lightweight block ciphers are mostly expressed for encryption routine and efforts are made to keep it as light as possible mostly in terms of gates count and power usage although some try to keep ...
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Bit Flipping Attack on CBC Mode

To perform a bit flipping attack, the previous block is modified by using XOR. This results in an altered plaintext. However, now the ciphertext of the previous block is altered, hence it will result ...
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Would this mode of operation be safer?

Here the key stream is used as keys for the second level of block cipher encryption. I guess this is not vulnerable to: padding oracle attack because it is basically counter mode stream cipher ...
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Combining stream cipher with block cipher for disk encryption

You take something like chacha20 and use the disk block # to seek it, xor it with the data block and then encrypt it with a block cipher in ECB mode. Would this be secure? Edit: To avoid getting ...
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683 views

What's the difference between confusion/diffusion and mode of operation?

I understand the concepts of confusion (substitution) and diffusion (permutation). My understanding of what a mode is that it's an algorithm that lets us encrypt arbitrary message size. i.e. AES is ...
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79 views

Permutation and modes of operation

I'm reading the book "Serious Cryptography A Practical Introduction to Modern Encryption" from Jean-Philippe Aumasson, and in the first chapter, it is written this : We can try to abstract out the ...
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1answer
536 views

Known Plaintext Attack for Modified OFB Mode of Operation

Question: Assume a variant of the OFB mode by which we only feedback the 8 most significant bits of the cipher output. We use AES and fill the remaining 120 input bits to the cipher with 0's: Why is ...
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Known Plaintext Attack on Block Cipher in ECB and CBC Modes of Operations

These 2 similar questions are from Paar's Understanding Cryptography. I could not see the answer so if someone can help I will appreciate: Question1: We consider known plaintext attacks on block ...
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Are there recommended modes of operation for lightweight ciphers?

There are many recommended modes of operation for block ciphers as described by NIST here, e.g. for DES and AES. However, I am struggling to find any for lightweight ciphers. I am particularly ...
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TLS ciphersuite without mode of operation

Will there be any security concern if there is no mode of operation specified in the ciphersuite name? For instance, there is no mode of operation in ...
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519 views

“Weak” implementation of AES-CTR?

Assume an instantiation of AES-CTR like in the following picture: Some details on the input-values for keystream generation: COUNT: a 32-bit value associated with ...
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AES blocks with a counter

I would like to send small separate packets of data. I am thinking of using AES-128 or AES-256, and to add a counter as part of the plain text message. Some clarifications: Each message will be one ...
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99 views

AES without mode operation

i have field in database. ex: field name. this field maybe more than 16 byte. how to encrypt data more than 16 byte without cbc, etc? any function or another ways to do this?
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Which block cipher mode to use?

I am working on securing a chat application, and I am not sure about which block cipher mode I should use. I am aware that I should avoid ECB as it's insecure, but what about CBC? I have watched ...
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284 views

Does it matter how the IV and XOR are applied for a single AES-128 block?

I want to encrypt 128 bits of data. I understand the problem with ECB, so I generate a 128-bit Initialization Vector to use for encryption and send with the encrypted data. Is there a "best" way to ...
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3DES Feasibility and Security [closed]

Questions are as following: Is 3DES still feasible (in terms of security and performance) to use? Is 3DES safe to use in ECB mode? Every time on giving the same input (plain text) to encrypt via 3DES ...
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Can we replace IV increasing from addition to XOR in CTR mode?

In CTR mode (not nonce-based), if we have ${IV}\stackrel{\$}{\leftarrow}\{0,1\}^{128}$ and want to encrypt message blocks $M_1, M_2, ..., M_\ell \in\{0,1\}^{128}$: The ciphertext is $IV\parallel C_1\...
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Is it safe to calculate the counter based on the block number in the stream rather than increasing it every write?

I've come to use AES/SIC for my purpose as I want to write an encrypted file and read it back with the possibility to seek (I only need to read parts of it and don't want to decrypt the whole file ...
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Is this method of speeding up a symmetrical algorithm secure? (AES output joining)

I was trying to find out a way of speeding up a given symmetrical algorithm the reason and programing launguage in this case are unimportant. I have came up with the following thing: Divide data into ...
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Propagating CBC insecure Authenticated Encryption

why is Propagating CBC (PCBC) insecure for authenticated encryption? I received the hint that I should feed a message of length $n$ and a message of length $n-1$ to it, but I don't really get what the ...
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Random Access vs. Parallelism modes of operation

I am trying to understand some concepts regarding Random Read Access and Parallelism in mode of operations. I have written below what my concepts are regarding the two. If you can please correct where ...
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Why do we only encrypt nounce + counter in Counter Mode?

I do not understand, what the advantage is in only encrypting the nonce + Ctr and XORing this to our plaintext, instead of encrypting everything. (If our block cipher can be easily decrypted) What ...
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Text partially decrypted regardless of IV

I'm trying to work out which AES cipher is best to use. I'm working with the OpenSSL ruby gem. While testing the various options I noticed that most of the ciphers result in partial or even full ...
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Is error propagation desired in modes of operation

I'm taking a very simple class on cryptography. The class is not mathematical is just the very basics. We learned about modes of operations recently (such as CBC and CTR), one of the things I learned ...
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Extending IGE to provide authentication

I was playing around with the idea of modifying infinite garble extension (IGE) mode to provide authentication in one pass. I was also doing some Google searches today to see if there were any ...
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Is PCBC using XOR still susceptible to adjacent swap attacks if a permutation is used?

PCBC with XOR as the operation used to combine the plaintext and cipherext blocks is vulnerable to adjacent swap attacks. But is it still susceptible to this attack if one of the following is done: ...
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Which block cipher mode(s) can perform most of the decryption work in parallel?

Codebook (ECB), Cipher Block Chaining (CBC), Cipher Feedback (CFB), and Counter (CTR). Which of these four modes can perform most of the decryption work in parallel? Why?
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Why use CCM instead CBC-then-MAC?

Is there any reason why CCM was created with encryption/decryption being done with a counter versus using CBC-then-MAC?
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Why is SIV a thing if MAC-and-encrypt is not the most secure way to go?

The question that I am asking is exactly what I ask in the title.
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Why does the Gameboy Advance serial encryption include the destination byte address?

The Gameboy Advance encrypts data sent over its serial port. It assembles a random number to seed a linear congruential generator. Then, it xors this PRN, the data, a symmetric key, and the byte ...
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Upper bound of this derivative of counter mode?

Suppose that: $\boldsymbol{K} \in \{0, 1\}^{\ell_{K}}$. $\boldsymbol{IV} \in \{0, 1\}^{\ell_{IV}}$. $\boldsymbol{I} \in \{0, 1\}^{\ell_{I}}$. $\boldsymbol{X} \in \{0, 1\}^{\ell_{X}}$. $E(K, X): \...
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Aes 128, CTR mode, Counter Mode, Hmac, mac

Assume Alice and Bob are communicating using 'MAC then Encrypt' paradigm. Specifically, they are using HMAC with SHA256 as the hash function and the output is truncated to 40 bits. They are using AES-...
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Using an Even-Mansour block cipher in a tweakable mode of operation

Assume that: $P(X): \{0, 1\}^{\ell_{X}} \rightarrow \{0, 1\}^{\ell_{X}}$. $Q(X): \{0, 1\}^{\ell_{X}} \rightarrow \{0, 1\}^{\ell_{X}}$. $E(K, X): \{0, 1\}^{\ell_{K}} \times \{0, 1\}^{\ell_{X}} \...
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Does XEX mode specify how the whitening value is generated?

When the term "XEX" or the phrase "XOR-encrypt-XOR" is used, does it refer only to the scheme $CT = E_{K}(PT \oplus T) \oplus T$/$PT = E_{K}(CT \oplus T) \oplus T$ (where $T$ is the whitening/tweak ...
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Cryptopals challenge 2.11: Distinguish ECB and CBC encryption

I'm going through the Matasano crypto challenges (also known as cryptopals) and I recently got stuck in the following challenge: http://cryptopals.com/sets/2/challenges/11 The goal of the challenge ...