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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Why do we need nonce in the CTR mode given that Deterministic counter mode is semantically secure?

In the CTR mode, a nonce, a counter value and the key are needed to form the input of the PRF. However, the Deterministic counter mentioned in Dan Boneh's slides (https://crypto.stanford.edu/~dabo/...
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What is "entropic security"?

I've come across a form of cryptographic security that I've never heard of: entropic security. I've read the Russel et al abstract and that doesn't seem to bear much relation to the wiki article. ...
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Pros and cons about padding a cryptogram produced with an "additive" operation mode

These days I found myself thinking about the implications of padding or not padding block cipher modes that act like additive stream ciphers (I meant OFB, CTR, GCM etc). Let's call additive modes. You ...
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Encrypting a random block with XTS and XORing into the plaintext: Would this encipherment scheme be secure?

I had an idea to make XTS mode parallelizable at CPU level. Let's suppose I take two AES-256 keys for XTS and encrypt a 512-byte block with this block cipher mode and XOR the output into the plaintext....
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Could this scheme work for multiparty computation secret sharing?

Suppose that there are $5$ players and each of them learns a secret that is a coordinate of the random vector $s=(s_1,s_2,\cdots,s_5)$, such that $s$ is a uniformly distributed over the field $V$. ...
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ECB... lacks diffusion(?)

I noticed that the wikipedia page for 'block cipher modes of encryption' states, "The disadvantage of this method is a lack of diffusion.", referring to ECB mode for block cipher encryption. ...
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What is aes in "operational mode"

I'm currently reading this report on the security of the IOT protocol "LoRaWAN". On page 3, it says the following: ...
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"Fixing" PCBC mode?

In PCBC mode, one encrypts and decrypts via $$ C_i = E(P_i \oplus P_{i-1} \oplus C_{i-1}) \Longleftrightarrow P_i = D(C_i) \oplus P_{i-1} \oplus C_{i-1} $$ (where $P_0 \oplus C_0 = IV$), which has ...
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CTR mode calculate messages before new key is required

I am studying a cryptography video on Coursera here titled: Modes of Operation: Many Time Key (CTR). I have just two simple questions: At around 4:30 in the video they show 2^48 without saying where ...
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CTR overlap with random IV

Problem: I'm slightly worried about counter repeats in CTR mode when using random IV. If you split it (like half IV, half counter), it increases chances of same IV (it is smaller) and limits message ...
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Why are block ciphers mostly used as stream ciphers?

Using a block cipher with using either CTR or GCM mode gives us a stream cipher, the only difference being that CTR does not include a MAC tag or AAD but GCM does. I think these are the most commonly ...
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How to minimize AES output size?

I work on a project about CAN bus and I want to encrypt the data among nodes but I have have a problem because CAN bus nodes receive and send 8 bytes among each others and I know the size of AES ...
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AES plaintext is smaller than 128 bits [duplicate]

I'm currently developing a AES implementation in a graduation project at university. As far as I know, AES uses a 128 bit block length as input . if the entered string to encrypt is not 128 bits such ...
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Can ChaCha20 provide integrity?

I have read that in general stream ciphers do not provide data integrity. Can ChaCha20 be implemented in such a way (perhaps like counter mode with message authentication in AES) to provide this?
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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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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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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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does CFB support random read access?

According to Wikipedia block cipher modes of operation, simplified CFB supports random read access. but what about the real CFB where we have a shift register? below are pictures extracted from the ...
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CBC mode works well for input greater than "b" bits. What is that "b" bits?

This post on geeksforgeeks.org about block cipher modes of operation, says that one of the advantages of the CBC is that it works well for input greater than b bits. I also saw that in the book "...
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Bulk encryption with Triple Blowfish

Blowfish has a large key setup penalty, except is fast once it gets rolling. I believe that before AES optimizations became commonplace, it was faster than AES after the initial key setup. It's top ...
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Zerologon question - AES-CFB8

I was reading the zerologon whitepaper by secura named: Unauthenticated domain controller compromise by subverting Netlogon cryptography. I'm trying to understand the zerologon attack. The issue is ...
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Correctness of Propagating Cipher Block Chaining mode of operation (PCBC)

I was looking at the Wikipedia article about Block cipher mode of operation and I was wondering how can you from the encryption $C_i = E_K(P_i \oplus P_{i-1}\oplus C_{i-1})$ get the decryption $P_i = ...
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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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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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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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Which encryption mode is best for transport of random values?

I was wondering which block encryption mode or modes will be most appropriate for transport of random values of one-block length. Block length could be of size 256 bytes and transport is from person ...
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The smallest secure block size [duplicate]

I have designed an encryption algorithm. The algorithm will probably use CFB mode. The algorithm can encrypt any block size and this does not change the size of the key. There are always about $20$ ...
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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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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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Why is XEX not used instead of CTR?

As far as I know the only disadvantage that XEX has when compared to CTR is that you need a block cipher/permutation while CTR is fine with just a hash function. Meanwhile XEX offers the advantage ...
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Repeating nonce in CTR mode

Can anybody explain in detail why repeating nonce is dangerous in CTR mode? Two cases to explain When plain text is repeated for each nonce. When plain text is unique for each nonce .
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How to apply a block cipher to (large) packetized communication when packets can get lost/erased?

In light of current events (Zoom getting strong headwinds for using AES-128 in ECB mode), I was wondering what the general approach is to packetized data encryption, where the packet length (UDP for ...
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What is the difference between cfb and cfb1 and cfb8 ? ( like openssl's aria-128-cfb & aria-128-cfb1 & aria-128-cfb8 )

What is the difference between cfb and cfb1 and cfb8 ? like openssl's aria-128-cfb and aria-128-cfb1 and ...
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Modes of operation that simply uses the tweak of a tweakable block cipher

What is the name of the mode in which we simply change the tweak for each block without the need for complex chaining modes? Is this mode secure? Are there any other recommended modes for native ...
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How to figure out DES mode used given plaintext and ciphertext?

In DES, I'm given the following exercise. - How can I find out which part of the plaintext each ciphertext message corresponds to, and which mode they were each encrypted with?
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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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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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Regarding XEX mode

Wikipedia claims that given an unkeyed permutation $p$ (presumably of the same size as the key) this is safe: $p(m \oplus k) \oplus k$ Why isn't this construction used instead of XEX? Surely unkeyed ...
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Interleaved CBC

I've been researching cryptographic modes and came across an obscure mode called interleaved CBC (ICBC). I can't find a lot about it and am wondering if anyone knows anything more. It's basically CBC ...
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IND-CPA security of mode of operation using triple AES with plaintext || IV+counter

I have found this figure of a mode of operation using a triple AES with m||IV+ctr input: I suppose it's a custom mode of operation since I haven't seen it anywhere else. My question is if it is IND-...
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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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What are the popular modes-of-operation (AES-GCM, AES-SIV, AES-GCM-SIV, etc.) geared for?

I'm interested in developing software capable of encrypting personal files (which will ultimately be backed up to the cloud) and have been doing my best to follow best practices. There are many forms ...
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Why is the second XOR operation in OCB mode necessary?

In Rogaway's OCB mode, the offset (derived from the key) ist XOR-added twice: Once to the plaintext block, and a second time after the Encryption. I am wondering, why the second XOR operation is ...
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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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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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