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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Is there a strong cryptographic reason for GCM's 2^39 - 256 bit limit, why Not 2^39 [duplicate]
While examining the initial GCM specification by McGrew and Viega in 2005, it appears that the formation of the 128-bit Initialization Vector by combining a 96-bit nonce and a 32-bit unsigned wrapping ...
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How secure is half-key Even-Mansour?
Single-key Even-Mansour is secure up to $2^{0.5 \times n}$. Where $n$ is permutation and key size.
Would using $n/2$-key retain same security as $n$-key?
Could the other half be used as a tweak?
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Recommended way to generate a key and IV for CFB mode?
I need to generate a key and IV that will be used to encrypt multiple things over a period of time with AES in CFB mode. The decision to use AES in CFB mode is not mine to change and the key will only ...
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Is it a bad idea to swap modes/encryption primitives?
I was wondering if changing modes or primitives could affect security. For example, let's say you have encrypted data with AES-128 with CBC mode and you want to change it to AES-128 GCM, or to ASCON. ...
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Is it undesirable for authentication to require decrypting a ciphertext?
A couple years ago, I devised some primitives for block ciphers and block cipher modes of operation; I was partly inspired by CAESAR. What these designs all had in common is that the encryption/...
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Are modes like CBC, OFB, CFB subject to chosen plaintext attacks?
I haven't found much info on the internet about the weakness of modes to chosen plaintext attacks, but from what I understand of them, there seem to be some trivial attacks, so I'm a bit confused.
For ...
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Is there a Block cipher (mode) with a not symmetric variable which if it is altered always produced a different cipher?
The BC should look like this
$$BC(m,k,n) = (c,n')$$
$$BC^{-1}(c,k,n') = (m,n)$$
with the additional variable $n$ not symmetric, so in almost all cases:
$$n \not= n'$$
$m$... plaintext
$c$... ...
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What mode in EVP for AES-128 should I use for cryptanalysis of AES?
I've been trying to use AES from OpenSSL and got to know that I need to use the EVP-based implementations rather than the AES_*.
I need to use AES-128 ...
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Vulnerability due to same IV, same key, same plaintext at same position in OFB
I am currently studying OFB mode, and one of the vulnerability mentioned for it is that if two different messages have a block at the same position in the ciphertext, and have same plaintext, the ...
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Authenticated Encryption with Length Expansion for Storage Devices
Recently, I've been working on disk encryption. I started with the AES-XTS mode which is the standard for this purpose and tried to understand the concept of disk encryption in general.
I know that ...
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Which ciphers have been defined that use the Keccak sponge?
There seem to have been defined multiple ciphers using the Keccak sponge as building block / primitive. These seem to have escaped public attention, possibly because they have not been standardized ...
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What would be the maximum acceptable block size for disk enryption?
AES-256 in XTS mode has 32x16 (512) bytes of blocksize but there are some other wide-block modes of operation such as WCFB which accepts any block size.
My question is:
What is the maximum acceptable ...
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Can the encryption with CTR mode be replaced by a publicly known unkeyed permutation when doing multiple encryption and keeping the IV secret?
A user of this forum answered in one of my questions and said that if the IV is kept secret in multiple encryption with CTR mode, the cost of breaking the scheme is $${2^{2 l_{key}}} 2 \cdot {2^{l_{iv}...
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Can attacker create encryption of message m XOR 1^n given the ciphertext c, in nonce-based counter mode?
The following question is from Stanford cryptography course final exam paper.
Suppose an attacker intercepts a ciphertext c which is the encryption of a message m ε {0, 1}^n under nonce-based counter ...
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Modification of CFB Mode of Operation?
To encrypt plaintext $(P_1, P_2, P_3, ... P_n)$ Ciphertext Feedback Mode (CFB) works as follows :-
$$
C_0 = IV \\
C_i = E_K (C_{i-1}) \oplus P_i
$$
Lets define a modified version of CFB mode as ...
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Why is ECB mode unsafe if the key is kept secret?
this is my first post so I apologise if the formatting of my post isn't perfect.
I should start off by saying that this post is not for any malicious intent, rather for curiosity and understanding AES ...
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Why do we need nonce in the CTR mode given that Deterministic counter mode is semantically secure?
In the CTR mode, a nonce, a counter value and the key are needed to form the input of the PRF. However, the Deterministic counter mentioned in Dan Boneh's slides (https://crypto.stanford.edu/~dabo/...
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What is "entropic security"?
I've come across a form of cryptographic security that I've never heard of: entropic security. I've read the Russel et al abstract and that doesn't seem to bear much relation to the wiki article.
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Pros and cons about padding a cryptogram produced with an "additive" operation mode
These days I found myself thinking about the implications of padding or not padding block cipher modes that act like additive stream ciphers (I meant OFB, CTR, GCM etc). Let's call additive modes.
You ...
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ECB... lacks diffusion(?)
I noticed that the wikipedia page for 'block cipher modes of encryption' states, "The disadvantage of this method is a lack of diffusion.", referring to ECB mode for block cipher encryption.
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What is aes in "operational mode"
I'm currently reading this report on the security of the IOT protocol "LoRaWAN".
On page 3, it says the following:
...
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"Fixing" PCBC mode?
In PCBC mode, one encrypts and decrypts via
$$ 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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