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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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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184 views

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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477 views

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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283 views

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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86 views

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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565 views

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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80 views

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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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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254 views

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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56 views

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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71 views

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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236 views

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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201 views

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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296 views

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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485 views

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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163 views

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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208 views

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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223 views

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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153 views

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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698 views

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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778 views

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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161 views

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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196 views

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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631 views

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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59 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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947 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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322 views

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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708 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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