# All Questions

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### Accidently deleted “~/.gnupg/pubring.kbx” , how to recover keys [migrated]

is there is any way to recover the encryption keys in this case, since they really important 1) the issue: i've lost my gpg key identifiers by deleting ...
33 views

### security parameter in lattice cryptography

In paper Lattice Signatures Without Trapdoors(Lyubashevsky2012), $n$ is the security parameter, why the authors set $n$ as 512 but not 80/100/112 to get 80-bit security/100-bit/112-bit security?
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### Can an AES-GCM be cracked if the key is known but the nonce isn't?

I'm kind of new in this field and I've been trying to learn it. I'm now facing an issue where I have a couple of packages encrypted with AES-128 GCM and I have the key that was used to encrypt these ...
62 views

### How to backup a secret encrypted by multi parties without revealing the secret?

I'm searching for a way to backup a secret that only the end user knows the information with 2 trusted hosts. But trusted hosts shouldn't have access to secret at any time. First basic version : ...
67 views

### Can there be more than one valid private exponent for a given p, q, and e in RSA encryption?

For example, given: p = 173, q = 149, e = 3 Using phi(n) gives d = 16971 While using lambda(n) gives d = 4243 Both values satisfy the checking equation (de)%phi=1, so are both correct, and if so, ...
45 views

### How does re-hashing affects security strength?

I am currently saving hashed passwords for my website. Passwords are salted and then hashed using SHA3-512. I understand the security level of SHA3-512, as it is for all Keccak algorithms, is half the ...
65 views

### Anonymous location hashing

Is it possible to know if two geographic locations are within a certain distance of each other without revealing the location? I'm thinking about contact tracing during the COVID-19 outbreak. ...
136 views

### why after saving File becomes larger? Steganography [closed]

274534d7d1780203956040e16a2fd8712e21596c92d7ac2ecd959d0166f8a501 I am trying to solve this puzzle. Source program is unknown. However after saving the file from editor it becomes larger than original....
971 views

### Why do people criticize and mistrust the e-voting based block chain?

I am planning to implement an e-voting system based on hyperledger fabric blockchain, however, I came across many criticisms from well-known security experts like Josh Benaloh and others. The problem ...
29 views

### Is it possible to “convert” to a curve

Assuming I have a 2 black boxes Box A: generates a private key and use it to sign whatever data I sent it (using secp256r1). It also returns the corresponding public key Box B: gets a public key, and ...
60 views

### Fully homomorphic encryption (over addition and multiplication) library in python

I was wondering if there is a commonly used library in Python (or another common language such as Java, C++, etc.) for fully homomorphic encryption over multiplication and addition that also supports ...
23 views

### Mac-sforge motivation for storing pairs

I don't understand why Q keeping pairs of instead of m like mac-forge solves the problem of generating a new tag on a previously authenticated message. Say, a previously authenticated message for "...
27 views

### I need help deciphering this [closed]

I'm not sure if this is the right place to ask this, but I need help deciphering this code. Message is as follows: "I,Zdg F\ух|Rю.DpьфоF}"rxVдrGGMjWяьеmqлiWaюeBseцюagаmьFsa-j|=d,фgdмeZvйwfmHlArцxπ"...
24 views

### CSPRNG unique seeds and proving uniform output [closed]

I have two related questions concerning cryptographically secure pseudo random number generators. My first question is as follows: are there conditions on the definition of cryptographically secure ...
39 views

### Provably secure way of expanding permutations

Gimli is a 384-bit permutation which makes use of an internal 96-bit permutation which works on columns. Every 4 rounds starting from the 1st a "small swap" is performed and every 4 rounds starting ...
50 views

### SHA-256 security for initial 32 bits

I have concerns regarding truncated SHA-256 hashes in an application I am building at the moment: Nomenclature secret - the full 256-bit SHA-256 result of hashing ...
125 views

### Why did the NSA create SHA?

new to cryptography, i'm trying to learn the program veracrypt, and i'm now trying to understand the history of hash functions and how it applies to veracrypt. so this is what i understand so far, ...
31 views

### ECDH Public Key Recovery - Determine if valid key exists from just signature and message

If I have just the (r,s,v) values of the signature and the message hash, what is the most efficient way to determine if a valid public key exists? I do not need to know the public key, just that the ...
37 views

### How can I get VMAC Code in pure c?

I had find a paper about VMAC algorithm:VMAC: Message Authentication Code using Universal Hashing. Now I want to implement this algorithm, But i don't find test vectors about it. Who can give some ...
45 views

### Is XChacha20 - Poly1305 Quantum resistant?

This is a question just out of curiosity, as I am a newbie to Post Quantum Cryptography. I have read several articles where they emphasize that current standardised symmetric encryption algorithms (...
31 views

27 views

### Prove linkage between secret keys

Hey guys I'm not a crypto expert so apologies if the question is especially noobish. We have a web application that requires the user to sign certain messages. We have been storing the secret key in ...
30 views

### How to calculate the redundancy of a language

I originally asked this question on the information security stack exchange but I think it's better suited here. I'm trying to calculating the unicity distance for a cipher applied to a language I ...
54 views

### If I allow arbitrary initial hash values for SHA-256, what would be the weaknesses?

The initial hash values (IV) of SHA256 are fixed. However, let's say I modify the SHA256 hash function to allow the attacker to use arbitrary IVs rather than fixed IVs. What kind of weaknesses would ...
25 views

### Encrypt and decrypt data accessible by two users on the web on multiple devices

I am currently building a website where a user will be able to upload a file to my server and another user will be able to download the file. Now i want to add encryption to this with the following ...
16 views

### Does every 256 bit number have a distinct sha256 result? [duplicate]

If I were some how able to create a table of all 256 bit inputs and outputs of sha256, would each of the inputs have a distinct output?
61 views

### How is asymmetric cryptography safe if one of the keys is public?

Let's suppose $A$ is sending a message $m$ to $B$ using asymmetric cryptography. To guarantee the authenticity of a message, $A$ encrypts $m$ with $A$'s private key: $E(m, k_A) = m_A$. Then, $A$ ...
9 views

### How to store private keys in browsers after Apple's decision to wipe script-writeable storage? [migrated]

We have a web application that puts a private key in LocalStorage, which enables users to sign off certain messages. It's been working fine until today we saw this announcement from Apple, https://...
10 views

### Finding IV in AES-128 having partial Key and plaintext

Let's suppose we have the plaintext, 14/16 char of the key and the first 2 and the last 36 chars of encrypted data (that is 64 char long). What I want is to find the IV. The cipher algorithm is AES (I ...
42 views

### Can any part of AES encrypted blocks be used as PRFed value?

Suppose we need a PRF whose output space is 255bit. Then, what I can do with AES with 128-bit security is producing 2 AES blocks that are of 256-bit. Then, I will remove the most significant bit of ...
114 views

### Why is Curve25519 mostly used for key exchange?

When i studied the Applications where Curve25519 is used, i found out, that it is mostly used for the key exchange. Examples are the Signal Protocol and Threema. I know, that Curve25519 has a pretty ...
64 views

### Why the output of elliptic curve based cryptosystems is smaller than the ordinary public key cryptosystems?

I am trying to understand how much the output of elliptic curve based cryptosystems (for example elliptic curve ElGamal) is smaller than the ordinary public key cryptosystems. I know that the ...
33 views

### Learning with rounding (LWR)

This may be a naive question: LWR assumption states that for ${A} \stackrel{$}{\leftarrow} \mathbb{Z}^{m \times n}_q, s \stackrel{$}{\leftarrow} \mathbb{Z}^n_q$, given $(A, \lfloor A\cdot s \rfloor_p$...
38 views

### Behavior of AES-CTR with 128-bit nonce and possible overflow

If I feed 128 bits of randomness into AES-CTR as its IV / nonce / initial counter, what will happen if I feed in a random 128-bit integer that overflows and wraps around? I've written a test for this ...
167 views

### Why are there standards of encryption?

Pardon me if this question seems a bit obvious, but if someone has a key to your encryption, knowing what type of encryption you are using (or running outputs against a lot of common encryption types) ...
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### Which is the best algorithm for large scale file encryption other than AES?

I've been looking for a fast, powerful and robust algorithm for encrypting large files with authentication . I would like to implement the algorithm on my own without using third party software. I've ...
26 views

### Decoding in Reed solomon codes

I have code encoded in GF(7) with primitive 5 Сf(4,1,0,4,5,5). (last four symbols is redundancy) While decoding using DFT we use formula $$С_k=N^{-1}*c(z^{-kj})$$ example:  C_1 = c(5^{-1*j})/6 ...
32 views

### Very simple way of verification

In an application we need some way for a user to authenticate, but have the challenges of very restricted functions to use. Each user has got a 16bit-number he can't change. We want to calculate some ...
117 views

### Entropy Preserving Functions

Let F be a deterministic compression function that takes fixed length 128 bit inputs and outputs 8 bits. Each input to the function has 128 bits of entropy, does that mean that the output byte has 128 ...
23 views

### Block size of BKZ algorithm and related security of CRYSTALS-Kyber

Security of lattice-based schemes in the NIST Posto-Quantum Project often relies on the complexity of dual attack. Complexity of this attack depends on the running time of lattice basis reduction ...
29 views

### Packing technique for large data storage

Packing multiple plaintext messages into a single ciphertext block is known to increase the effeciency of homomorphic encryption. Can someone let me know if this technique can support large data ? For ...