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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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49 views

What does XOR mean in regards to AES cryptography? [on hold]

This might be too basic to answer but I am learning about the different modes of operation and I am trying to grasp the material and having trouble deciphering the meaning. I was just wondering if ...
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1answer
50 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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3answers
76 views

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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2answers
107 views

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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1answer
154 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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2answers
109 views

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 ...
5
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1answer
439 views

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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1answer
239 views

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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0answers
64 views

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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3answers
237 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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1answer
54 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
169 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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1answer
234 views

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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1answer
95 views

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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4answers
59 views

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 ...
4
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3answers
211 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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2answers
91 views

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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1answer
82 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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1answer
185 views

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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1answer
106 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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1answer
71 views

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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1answer
66 views

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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0answers
47 views

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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1answer
84 views

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 ...
3
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1answer
73 views

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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1answer
79 views

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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1answer
58 views

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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4answers
699 views

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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3answers
726 views

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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0answers
38 views

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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0answers
48 views

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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1answer
507 views

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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1answer
370 views

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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3answers
293 views

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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1answer
109 views

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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0answers
44 views

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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1answer
333 views

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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66 views

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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102 views

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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1answer
458 views

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 ...
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1answer
171 views

How does CCM handle variable-length messages?

Since CBC-MAC is insecure for variable-length messages if nothing is done to handle them, I'm wondering how it can be used with variable-length messages. Rogaway's critique of CCM indicates that it ...
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3answers
5k views

Why was AES CBC removed in TLS 1.3?

I don't quite understand why AES CBC was removed in TLS1.3 . from what I know CBC is the most secure Mode of operation for the AES block cipher ( if you can say it like that ) It only needs a TRND IV ...
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2answers
613 views

Security of AES in CTR mode with fixed nonce (but different key)

If I am using AES in CTR mode and use a unique key every time but the same nonce, is this secure? If so, does it make a difference if the nonce is public?
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1answer
56 views

Desirability of chaining an LCG in an authentication scheme

Suppose that: $E(k, x)$ is the encryption of data block $x$ with key $k$ using a block cipher. $L_{Key}$ is the key size of the block cipher in bits. $L_{Block}$ is the block size of the block cipher ...
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0answers
80 views

What are the malleability properties of block device encryption with multiple modes of operation?

When encrypting a block device with a given symmetric cipher with a 128-bit block size in CBC mode, every second plaintext block in a sector can be changed to contain arbitrary data, with the blocks ...
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3answers
537 views

Maximum Number of Blocks to be Encrypted under One Key in CBC and CTR Mode?

What is the Limit on Maximum Number of Blocks to be Encrypted under One Key in CBC and CTR Mode? What happens if the limit is crossed and more number of blocks are encrypted?
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1answer
337 views

How can I encrypt more than 128 bits of data with AES?

To my understanding a state is a $4 \times 4$ byte array used to store the plaintext. That equates to $128$ bits of data. To encrypt more than $128$ bits of data do I need to setup multiple of these ...
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Security of this parallelizable two-pass authentication scheme

This is only the authentication half of a block cipher mode of operation that provides authenticated encryption. The part that provides encryption is left out (it can be CBC, PCBC, ECB, or whatever). ...
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106 views

How does “one-pass” authentication differ from “two-pass”?

The meaning of "one-pass authentication" as well as its difference from "two-pass authentication" has not been explained to my satisfaction. CCM mode, EAX mode, and HMAC are examples of the first type;...
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3answers
1k views

Is the CBC mode of operation a stream cipher mode?

I am taking a class on security systems. My professor considers CBC to be a stream cipher mode, like CFB and OFB. Most sources I have read do not agree with this, so I asked my professor about this, ...