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 secure is $\operatorname{AES256}_{\operatorname{ECB}}(\operatorname{ChaCha20}(\text{plaintext}))$?

Suppose I encrypt a bytestream using ChaCha20, and then encrypt the resulting ciphertext using AES in ECB mode. How secure is the combination?
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What is the Indexed Code Book Mode?

While reading specsheets for NXP processors (example mention in this PDF) the other day I saw the mention of the Indexed Code Book mode (ICB) for their AES acceleration hardware - the only mode they ...
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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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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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Unknown authenticated encryption mode

I'm running through a protocol specification (LoRaWAN, pdf), and I'm puzzled by the crypto. The data is encrypted and authenticated in the following way: a unique 128-bit key is used; the plaintext ...
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385 views

Is OCB the state of the art in authenticated encryption modes of operation for block ciphers?

OCB mode seems to represent the state of the art in authenticated encryption modes, largely due to its speed – it is faster than GCM even when GCM has hardware support. Its only drawbacks seem ...
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How can I read the AE figures?

This question is rather simple. I've recently read the paper "Automated Analysis and Synthesis of Authenticated Encryption Schemes". On page 17 of this paper the authors provide three figures of ...
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Increasing the diffusion of the AES-CBC encryption algorithm in pycrypto for python

When encryption is done using the AES-CBC algorithm, the encryption can be thought of as chaining the cipher texts with the previous ones and an IV. However, if its on CBC mode, we give our cipher ...
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Can XEX or XTS modes be used with only one tweak? (part 2)

This question is similar to Can XEX or XTS modes be used with only one tweak? except I am interested to know if one can instead use $X = E_{k}(0) \otimes \alpha^j \\ C = E_{k}(P \oplus X) \oplus X$ in ...
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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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56 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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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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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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82 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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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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Is it possible to create a detection oracle for all block cipher modes? — ciphertext-only cryptanalysis

I have made an ECB/CBC detection oracle, and am now trying to make a detection oracle that can differentiate between CBC/CFB/OFB/CTR/etc. I can already tell ECB apart from the others due to this ...
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Reykeyed AES in CTR mode as a stream cipher

Suppose one uses AES in CTR mode to generate a keystream, but every $l$ bytes the $n$ bits that would follow are used as a new AES key. Assuming that AES is a secure PRP: Is this a secure stream ...
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Synchronous Sponges

The paper The sponge construction as a source of secure cryptographic primitives (see Figure 6) mentions a synchronous sponge mode (working like CTR or OFB modes). So, this type of sponge is a non-...
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Is ECB mode more suitable than CBC mode while encrypting a long bit string?

I know that ECB is less secure than CBC, but will it be suitable for encrypting a long bit string?
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44 views

Is CMC/EME mode invulnerable?

I am looking for cipher mode to encrypt disk at a sector level 512B/4K Performance-wise CMC is not a problem here. There is no possibility to store additional data. Is there any other option without ...
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Where can I find test vectors of special mode of block cipher, such as CBCC, PCBC, EPBC, IOBC

Now, I am learning cryptography about block cipher. I plan to implement the mode of operator about it. I have know some modes, such as ECB, CBC, OFB, CFB, CTR. These modes are common and I have ...
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Is XEX/XTS good for deterministic file encryption?

My understanding about XEX/XTS mode is limited. But from what I see, it has two good properties: It is length-preserving so that encryption doesn't cost additional space. It is deterministic, which ...
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107 views

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 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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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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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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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;...