# All Questions

18,690 questions
9 views

### How do I decode an encoded string without a key in Ruby? (basic cryptography)

Is there a way to decrypt an encoded string without its key? Basically, I have a string that has been passed through three separate encryptions in the following order: Original -> Base64 -> AES-256 ->...
16 views

### Decryption an arbitrary cipher with XOR and rotation

I'm trying to find hidden 8-length long key from following XOR and Rotation based cipher. ...
92 views

### Von Neumann Extractor - Which bit is retained?

Which bit is retained in the Von Neumann debiasing algorithm? 00 and 11 are discarded and 10, 01 are retained but is the first or the second bit retained or does it matter? In other words: first: ...
10 views

### Cost model for different curve models

Is there a cost model for each curve model and their conversions? For example: Take the curve models: Projective, Completed, Extended, Affine. Is there a table which shows how many multiplications, ...
22 views

### Does it matter if I publish only publish good or bad hashes after recovering from a hack?

(This question is a follow-up from another question I asked about MD5, which is why I'm insisting on using MD5 in this question as well) My imaginary Linux distribution, Sushi Linux has had a big ...
20 views

### Can Shamir's SSS be augmented so that having the secret as well as half the shares necessary to construct the secret is enough to reconstruct the key?

More generally, is it possible to construct a $(k,n)$ threshold secret sharing scheme (i.e. let than k shares leaks no statistical information about the secret) such that possession of the secret ...
36 views

758 views

### Can we hide a text first in a picture and then hide that image again in one more image?

Can we hide a text first in a picture and then hide that image again in one more image? using a steganographic algorithm like Least significant bit (LSB)?
26 views

### How to exchange a common key to a group of person using Elliptic-curve Diffie–Hellman (ECDH)? [duplicate]

In ECDH, when two persons want to share private keys, they first select a point $G$ on the elliptic curve and after that, each of them picks a random integer $a$ and $b$, respectively, and multiply ...
49 views

### Reverse the order of encryption and decryption in CBC mode. Does this work?

To encrypt a message, one uses the algorithm for doing a CBC decryption. To decrypt a message, one uses the algorithm for doing a CBC encryption. Does this work?
14 views

### How users are in control of their funds? [on hold]

It is about DEX, how users are in control of their funds, while they should deposit in smart contract?
44 views

### Shamir's secret sharing for vectors

How would we go about building a scheme for Shamir secret sharing for vectors? I have already tried to use a vector of secrets and random distribution of the secrets to $n$ parties and then use $t$ of ...
13 views

### How to forge a Proof-of-Stake blockchain?

Suppose a node in a proof-of-stake blockchain network wants to forge a blockchain. I'm wondering what should this node do to forge it? Assume this node has a certain amount/fraction of money (but no ...
64 views

### How does PUF hardware help in software activation?

I have read that one of the PUF's application is software licensing, but do not know how. I have been reading different articles and forums (such as here), but still not clear for me. One vague point ...
30 views

### Maximum security strength in bits of ISAAC cipher?

Wikipedia claims key length can be very big in this cipher, so I assume it can offer a million bits of security provided entropy of key is the same? Of course I can SHA-256 hash the key to allow any ...
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### Security implications of an extra inner encrypt for a single block Matyas-Meyer-Oseas hash function

Was giving some thought to simple MMO constructions for fast single block hash functions for things like PQ crypto. There's Haraka, but that's not standard and readily available while simple AES is in ...
56 views

### Meaning of epsilon in proving a PRG is predictable/ un predictable

I am quite confused, I have been following a course on crypto provided by Dan Boneh, this is the lecture I am confused with - https://www.youtube.com/watch?v=EjWap3szsPk time stamp 8:58 - 11:00 I don'...
38 views

### How can I get select messages ciphers for salsa20poly1305 for unit tests?

In order to avoid memory errors, I always write safe C++ wrappers with strong type-safety for any C encryption library I use. To test my wrapper of ...
53 views

### How to compute a discrete logarithm modulo a power of 2?

This question is related to this one. Specifically, assume that we have $p$ = 2048, $m$ = 13 and $c$ = 357. In this case, $c\ =m^e\ \bmod \ p$. I know that many algorithms rely on the difficulty of ...
46 views

### How to find at least one private key from a large list of compressed public keys secp256k1

Not long ago I saw a discussion on the Bitcoin Talk forum: https://bitcointalk.org/index.php?topic=5060735.msg50736695#msg50736695 Please give advice and working methods? Is it possible to find at ...
37 views

### Are there a way to progress or age key pairs

I am searching for a way to make the noise X pattern fully forward secret. The X pattern is a way to encrypted and authenticated messages. As a building block to achieve this I started pondering if ...
42 views

### Check if two ed25519 points are equivalent

How to check if two points are equivalent given their projective coordinates (XYTZ)? For example if I do unproject() of a point to pass from XYTZ to XY coordinates and then I come back to XYTZ ...
54 views

### Who can create a MAC? Who can verify a MAC?

I have read many answers but I cannot get the basic explanation. There's no need for full details. I just need some basic information about who can create a mac and verify it.
31 views

### Efficient fields over arithmetic circuits

What sort of fields is efficient over an arithmetic circuit? Efficient meaning that given a field $\mathbb{F}_p$, reduction (modulo) does not require many multiplications and preferably inversion was ...
74 views

### How could I improve this general block cipher?

After looking at the Wikipedia page for the Fiestel cipher, I thought about making a variation of it that is very general. I basically followed the diagram on Wikipedia in order to structure the ...
23 views

### Unknown encoding with some known parameters [on hold]

I have a encoded hex values of 3 cipher text(encoded) and corresponding length of plain text too. The plain text and cipher(encoded) text is different in length. I also have some bytes of known Plain ...
57 views

### SHA256 message schedule examples

I need some example values for the message schedule stage of SHA256 to test this part of my implementation. If possible in binary, for the string 'abc'.
22 views

### montgomery reduction multiplicative identity

How do you figure out the multiplicative and additive identity with respects to R? I pick some R such that gcd(R, N) = 1 where N is the size of the group. Given some field element x in the group, I ...
7 views

### Initialization Vector displaying (Binary) using CBC in Python [migrated]

Hey is there a way to Print the (binary) version of the IV and not the Hexadecimal? I'm required to show it for class. I'm doing an encryption/decryption of plaintext using CBC mode and I have to ...
11 views

### AES - How do I write Inverse Sub Bytes in C++? [migrated]

How do I write Inverse Sub Bytes for AES Decryption in C++? I only found Sub Bytes for AES Encryption, which is shown below. ...
24 views

### Is there confirmation blocks in Proof-of-Stake Blockchain?

When I'm reading literature about proof-of-stake blockchain, I found that it seems there is no concept about confirmation blocks (which is used to confirm a posted transaction is indeed honestly ...
21 views

### good OmegaP for characteristic to use in differential cryptanalysis on DES

how to choose a good OmegaP(input difference) for the characteristic used in differential crypt-analysis on DES?
29 views

### Which cipher or encryption is being used here? [on hold]

My friend gave me this puzzle or code and I need to crack it for a game. The only hint they have given me is that kdjVDyb8QL means Think on it more.
33 views

### How can I follow the validation and verification recommendations of the NaCl (sodium) secretbox library?

I was advised to use crypto_secretbox_xsalsa20poly1305 due to its simplicity and because it's safe against timing attacks. I'm reading the secretbox tutorial, and ...
74 views

### RSA padding: risk of using constants

Assume I want to make my RSA secure because I heard that textbook RSA, especially in conjunction with low exponents, is very risky. I decide to limit my message length to 100 and subsequently ...
22 views

### Minimal secure index of quasi-cyclic codes for code-based cryptography

It is well-known that keys (generator matrices) of code-based cryptography are very large for its practical usage. To reduce them scientists propose to use families of quasi-cyclic codes. I remind ...
207 views

### Can Shor's algorithm factor multi-prime numbers?

I know that Shor's algorithm can factor semi-primes ($N = p \times q \space, \{p, \space q \in \Bbb{P} \space \vert \space p, \space q \gt 0 \}$). Assuming that all prime numbers are so large that ...
38 views

### Difference with round keys and round constant in AES

I am confused with round keys and round constant in AES. Are they the same? Can someone explain it to me?
836 views

### Difference between decryption and deciphering?

Is there a technical difference between decryption and deciphering?
36 views

### Cheating in (2,6)-Shamir Sharing Scheme

We consider a $(2, 6)$ Shamir secret sharing scheme over $Z_{11}$. Four players $A,B,C,D$ cooperate to find the secret, but one of them is cheating (so the share he claims to have might not be an ...
32 views

Say an attacker has access to a non-rate-limited API that takes (IV, data) and outputsAES-CBC(key, input, data), with the key ...
Suppose I have two messages $m_1$ and $m_2$ as well as $c_1$ and $n$. It's standard RSA so $c_1 = m_1^e \ mod \ n$, $c_2 = m_2^e \ mod \ n$. Further assume the only information we have about e is that ...