# All Questions

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### Point addition in NaCl/libsodium (Curve25519)

In NaCl and libsodium, the crypto_scalarmult function implements the operation $Q = kP$ (scalar/point multiplication). There doesn't seem to be a function for point ...
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### What if the p and q used in keys generation of Pailler cryptosystem are composite?

I've seen a few implementations of Paillier cryptosystem that uses probable primes to choose $p$ and $q$. Assuming that a keypair is generated with $p$ and $q$ that are coprime and that $pq$ is ...
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### What is the definition of “the correlation” and “the difference propagation probability”? [on hold]

Non linearity has two properties: 1. the correlation 2. the difference propagation probability what is the definition of each concept?
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### parallel shifters [closed]

suppose there is two registers each of size 8 bit and the inputs to these register are in parallel so can we combine this 2 register so that new combined register will have input 16 bits and all are ...
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### how can eve guess a pseudo-random key has been used for encryption [on hold]

I am stuck in my project and earnestly need suggestions for the above question
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### AES-CTR with ephemeral keys vs IV

Let's say that we have a key exchange of some sort, which leaves A and B sharing the long-term secret $S$. Then, A and B want to use AES-CTR for the communication, which leaves us with several ...
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### Attacks on elliptic-curve based cryptosystems through solving the Decisional Diffie-Hellman Problem with the Weil Pairing

Are there any examples of practical attacks on cryptosystems set over elliptic curves which utilize the easiness of DDH for certain choices of curves $E(\textbf{F}_q)$, and as such their lack of ...
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### Light weight crypto library implementations [migrated]

Are there any open source crypto libraries that can be used in embedded systems or in other memory constrained places like a boot rom? I am looking for libraries that I can compile only the algorithms ...
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### Basic cryptography [on hold]

{First of all I'd like to apologise about my English} I'm interested in most popular cryptography encodements, but ones, where the substitution cipher is known (for example Caesar's code), not created ...
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### PGP String to Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
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### Why should I make my cipher public?

As I understand it, the less people know about the internals of my protocol or cipher, the more secure the protocol is. However Kerckhoffs's principle states that A cryptosystem should be secure ...
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### Example: pre-image resistance to second pre-image resistance

It is possible to convert a pre-image resistant function $f:\{0,1\}^{n}\rightarrow \{0,1\}^{n}$ to a second-preimage resistant function? I am thinking to use a pseudo-random generator and construct ...
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### What consequences do the plaintext space size has on the performances in the BGV scheme?

In the BGV paper [1], the authors say in §5.4 that you can have $\mathbb{Z}_p$ as plaintext size with a large $p$. What is the impact of the size of $p$ on the ciphertext size and computational work ...
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### Help me find out what type of encryption this is. [on hold]

Alright this may not be an easy one. May not be something anyone knows. What I do know already (and I have made a password recovery tool from what I have learned) The password is translated into a ...
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### need help for decrypting a cipher.. i am new to this so was wondering if someone could tell me how to go about it [on hold]

how to begin to decrypt any numeric cypher? what are the basic steps to solve easy numeric cyphers?
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### Is there any such thing as “proof of location”?

I'm looking for a way for someone to prove to me their geographical location without a trusted third-party. Imagine wanting to prove to someone you're actually physically in a specific place. I'd ...
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### Why calculate pi to estimate randomness?

Why do testing suites calculate pi using the Monte Carlo method to determine if a series of numbers are random? As far as I can tell, the Monte Carlo method can be used to estimate pi itself (as a ...
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### I don't know whattype of cipher this is [on hold]

I am trying to solve the following sipher Nosdhiibotidcylhrdeovedljuetre I have no experience with ciphers but substitution didn't seem to work, and since its a long string without breaks process of ...
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### Is standardizing a modified AES a good idea?

"Recently" the Ukraine standardized a new block cipher Kalyna, which according to the abstract of"A New Encryption Standard of Ukraine: The Kalyna Block Cipher" by Oliynykov et al. (warning: the paper ...
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### Signature and hash function properties

I understand the need for the hash function to be collision resistant and second pre-image resistant. For what reason, exactly, does a hash function need to be pre-image resistant? If this property ...