# All Questions

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### How do Galios fields work in AES? [duplicate]

I am trying to learn how AES functions but I keep hanging at the subject of Galios fields. I am reading a lot about them but I just can not find an understandable explaination in how they work. Could ...
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### Can an adversary distinguish a private key from a pseudo-random string of the same length?

Apologies if this is a dumb question but allow me to describe the dilemma I have: Suppose that I am protecting a private key on a device using a password & PBKDF2. The obvious attack would be an ...
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### Insecurity of CBC-MAC

Can anyone explain why CBC-MAC is not secure for variable length message? I read many books, but there are still some confusion. Such as the highlighted parts in previous pictures ...
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### how a MITM attack works against tripartite in DH? [on hold]

Must Oscar change only the Key $K_{abc}$ (Alice, Bob and Charlie) or does he have one key for everyone of them ?
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### How does blocksize affect security?

I have recently read about how blockciphers and how stream ciphers work, and although I think I finally got everything right, I'm still wondering how increasing blocksize increases security.
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### Having trouble with a double encoded keyword sypher [closed]

IIYFATKOHRFDQLRTUKFOLDTIQLTFAZLGZFUNCKYCEFUCUQUGCWWOGYSOCZTXGZPNHYPMPQDOLNONAZOEQLUSEYELNUDEPQDOKPTIPQTYCZUZQQORUFANHQRGHIUJUQOEQQUWKEURLYHCSLUCUUUFKLUNAYLRUFAZQZONKYIGBKYITDOEAWGDPIKOOTRCUJLIGZWNSZGC ...
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### Can I use a block cipher in CTR mode to generate keys from a master key?

Suppose I have an AEAD mode based on a block cipher that requires two or more keys. In some cases, there is a complex proof that one key suffices. But finding such a proof is hard. An alternative ...
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### Why does RSA need p and q to be prime numbers?

This is a clarifying thread after finding: What makes RSA secure by using prime numbers?. Despite the fact that this question was answered already, I am still struggling to really grasp the ...
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### Man in the middle attack including 3 parties [closed]

How could a man in the middle attack work with 3 different parties in Diffie Hellman?
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### Is a chosen ciphertext attack on PGP still possible?

In a paper from 2002 (pdf), Jallad et al describe a chosen ciphertext attack on PGP by taking advantage of the CFB mode that the block ciphers use under PGP. It's quite a devastating attack. Is this ...
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### What is the diffrence between Feistel networks and SPN?

I recently read about the concept of Feistel Networks and Substitution Permutation Networks but what is exactly the difference between the two ?
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### Appropriate scrypt parameters when generating an scrypt hash

What values for CPU, memory and parallel difficulty should be used when generating an scrypt hash? i.e. ...
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Commitment scheme is given as follows: Alice chooses a random r the same size as x and calculates $y = h(x||r)$ where $||$ represents concatenation. Open: Alice sends x to Bob, and Bob calculates $y ... 2answers 54 views ### What does$\langle A, B\rangle$mean? I'm reading about CL-PKC and in Al-Riyami's FullIndent, I find some notations I must be sure to understand, to well explain it ... 1answer 79 views ### Is a composition of clocked entities a clocked entity in the UC model? In the book titled "Secure Multiparty Computation and Secret Sharing" the authors define an interactive agent and an interactive system. Further, the author defines a clocked entity for considering ... 1answer 39 views ### Order of multiple encryption algorithms as you can see on image above, in VeraCrypt you can select either Serpent -> Twofish -> AES or ... 0answers 9 views ### Time complexity looking up in a rainbow table It is mentioned in the famous paper Making a Faster Cryptanalytic Time-Memory Trade-Off by Philippe Oechslin that: The total number of calculations we have to make is thus$\frac{t(t−1)}{2}$. ... 0answers 32 views ### You can probably do this in your sleep [closed] I have been working on a geocaching puzzle for a long time I have solved all the ciphers except this: YLVEYF GIIKAH I have done what plain text attack I understand (mainly affine, one time and ... 2answers 46 views ### Motivation for the definition of statistical distance Statistical distance is a widely used measure in cryptography for comparing two distributions. One can define various other measures for capturing the differences between two distributions, but why do ... 1answer 33 views ### Which values to store in rainbow table generation? According to the Wikipedia and Philippe Oechslin's Making a Faster Cryptanalytic Time-Memory Trade-Off (pdf), both starting points and endpoints are keys. Here is an example from Wikipedia: As you ... 1answer 46 views ### Expire signature I am looking for a way to have a 'did it expired' key. There's a similar question here, but I have to prevent reusing of the 'did it expired' signature . A possible solution would be a two one-way ... 2answers 71 views ### How to break a 32 bit block cipher without key? From what I know Skip32 is the only 32 bit block cipher and I heard its not secure. What do I do or which tool do I use to break a 32-bit block cipher? I did search for this but all I find is attacks ... 0answers 27 views ### Deciphering encrypted / encoded tokens I came across this token on the web ADEAAAFUu6sBKnmU_y-KDL5sm5lAAEN9IPqq1wY and was wondering how can one go about understanding what encoding or cipher is used ... 0answers 33 views ### A symmetric key construction not based on XOR [closed] As far as I'm aware, one of the symmetric key constructions which is CPA-secure is$c = \langle r, m \oplus F_k(r) \rangle$. For designing a specific system I need a symmetric key construction which ... 1answer 900 views ### Hash algorithm with the least chance for collision Out of these algorithms… MD5 SHA1 SHA224 SHA256 SHA384 SHA512 … which has the least chance of collision, and which is the most secure at the time of writing this? 2answers 89 views ### What use cases would benefit from a faster RNG? The paper “Explicit Two-Source Extractors and Resilient Functions” (PDF) by Eshan Chattopadhyay and David Zuckerman is described by some as being a technological leap in RNG – opposed to slow and ... 1answer 40 views ### tweakable block cipher and ideal block cipher Can the set of block ciphers obtained from a tweakable block cipher (using distinct tweaks) be considered as the set of ideal block ciphers ? 1answer 41 views ### How secure is MD5 for one way authentication? I have a server S1 with an Private String (PS) as an identifier shared with a server S2. Every 10 min S1 publish the hash value of PS+the current time which is used as public identifier (PI). Every ... 0answers 22 views ### How to approach to solve cipher text with fixed length key (which is repeating)? I took a project to solve for lecture. In my project for a given cipher text(length 2031), I have a key (Picture of example is given.) which I do not know the length of it. So I started to try to find ... 2answers 296 views ### Security of the shared secret key for a smart meter (Linky) Reading the specs of a new electricity smart meter (called Linky in France), I was surprised about the chosen encryption method (128 bits symmetric key AES), based on a single secret key (called CCC ... 2answers 49 views ### Need help choosing algorithm and topic [closed] I am not pretty sure if this is the right place, but I have searched a lot and still cannot decide what to do. So here is why I am typing here - I am studying last year computer science and therefore ... 1answer 61 views ### What is the major difference between FIPS 186-2 and FIPS 186-4? Can anyone please tell me the major difference between FIPS 186-2 and FIPS 186-4? I know with FIPS 140-2 they want the DSS standard to be FIPS 186-4, but what difference does it make? 1answer 18 views ### How do two parties put together the AUTH data in the SKEME protocol? SKEME is a Key Exchange protocol used in the Internet Key Exchange (IKE). It contains three phases: SHARE, EXCH, and ... 1answer 71 views ### Quantum vs. regular computing time to break ECC? How long exactly would it take for a regular computer to crack an elliptic curve public/private key via bruteforce, vs. a quantum computer using Shor's algorithm with a couple thousand qubits? Can ... 1answer 66 views ### How many blocks can securely be encrypted with XTS I could not find in the NIST recommendations on XTS how many blocks can securely be encrypted with XTS-AES. Through the recommendations, I've found: The length of the data unit for any instance ... 1answer 23 views ### Single-scalar multiplication with sign bit I want to know if there's an "easy" timing-free way to compute the sign of$y$-coordinate of$r G$, for a secret scalar$r$and$G$the generator of an elliptic curve. We have several choices for ... 1answer 42 views ### Multiplying two additively shared values Alice has$p_a,q_a$and Bob has$p_b,q_b$, all elements of a ring$R$. They want to obtain shares of the value$pq$where$p=p_a+p_b$,$q=q_a+q_b$. How do they do this ? Does revealing their shares of ... 0answers 33 views ### Possible enigma settings? [duplicate] I'm writing an assignment about the Enigma machine, and i'm trying to calculate the amount of settings the enigma machine has. I have found several sites regarding this topic, but it seems like there ... 1answer 41 views ### Can Anyone Suggest The Simple App To Encrypt Messages? [closed] In the present scenario there are ways to snoop into someone's private communication. So in order to secure the communication encryption is the only way. Suggestions will be appreciated. Thanks 1answer 111 views ### differential cryptanalysis cipher for the final round I have a problem to find the sub-key. The system is… For each round, we make the following stage: We add the round key$K_i\$. Substitution : we have 8 blocks of 4 bits, and an S-box ...
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ZUC is a function that converts a string to another string. However, unlike a Hash function, ZUC converts a certain-length string to a any-length string. Can someone point me to its documentation or ...
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### How can I convert a mathematical formula into a logical formula?

I'm using cryptominisat2.9.6 to solve equation set (including more than 160 equations). There are 160 variables in total, which are as follows: ...
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### What is proper size of window Using RSA Window method?

I want to Use Window method for RSA modular Exponentiation. because of SCA. But I don`t know what is proper window size.
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### How to decipher English letters that had been encrypted [closed]

I tried several decipher methods (here and here) but still cannot find any. How do effectively decipher those below. Below messages are English that had been encrypted. i) DBEJIXCV IWTDGN XH WDL ...
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### Garbled table for 3 inputs

I have a truth table of a full adder with 3 inputs (A,B,Cin) and 2 outputs (S, Cout). How can I create a garbled truth table? I mean, in the general form it is ...
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### Does a key need to be signed if it is being used to decrypt a message that is already signed?

I am trying to better understand authentication. Lets say I have posted my 128-bit AES symmetric key on some forum, encrypted asymmetrically to my friend using 256-bit ECC (25519). The forum isn't ...
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### Encoded Output to ASCII for carving into objects. [closed]

I have a piece of text that I need to carve out into an object after some encryption. For this purpose it works better if I have alpha numeric output instead of with any special characters (like I get ...
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### Should I add randomness at the end before AES?

Seen AES, changing a character drastically affects the ecrypted text. I want to make it harder to decrypt AES I send. So, it seems this can be done by adding some special code and some random bytes ...