# All Questions

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14 views

### PBKDF2-HMAC Collisions

Trying to understand the well known property of these collisions when used with SHA1, SHA256, etc. where a given key is larger than the block size of the digest function. In these cases the smaller of ...
18 views

### Bruteforcing a symmetric cipher

I don't understand how we could bruteforce a symmetric cipher. Let's take AES with a key size of $128$ as an example. It means that there are $2^{128}$ possible keys, and as many ways to decrypt a ...
11 views

### Why are iterated substitution-permutation product ciphers only used on fixed-size plaintext blocks?

Another way to ask this question: when block ciphers were invented, why did they add the restriction that the block cipher would be restricted to blocks of a fixed size? From my laymen point of view, ...
13 views

### Zero knowledge proof for verifying a machine learning model

Imagine Alice has trained a machine learning model. Bob wants to verify that whether Alice actually trained the model or not, but Alice does not want to reveal her model (because the model is personal ...
35 views

### AES(CBC) XOR properties

I cant for the life of me figure this problem out, and I am having trouble understanding the XOR properties of CBC. I have input which is padded with PCKS7 and then encrypted using CBC. A hash is then ...
33 views

### Calculating symmetric key bit strength

16 byte key where each byte is in range 0-255, generated using cryptograhic PRNG will be believed to have 128 bit strength. What would be a bit strength of a key generated using same quality PRNG, ...
64 views

### What EC curve is used by Apple iOS platform?

I can't find information about EC curve used by Apple's iOS platform. The algorithm name that I could see in their docs is: ...
19 views

### Openssl sha1 key expand to 256 bits

Im trying to expand the sha1 key (160 bits) to 256 bits. Which is the right openssl evp function to use? Any suggestions? I have tried zero padding, padding like (01,02 02, 03 03 03,etc) but it doesnt ...
14 views

### Hash 'hashcat': Token length exception [closed]

hashcat64.exe hashcat -m0 -a0 crackme.txt password.txt Device #1: Intel's OpenCL runtime(GPU only) is currently broken. We are waiting for updated OpenCL drivers ...
20 views

### RSA accumulator exclusion proof without set

In researching about RSA accumulators I came across this question, Inclusion and Exclusion proofs in RSA accumulators - from the first answer I had assumed that proof of non-membership could be ...
19 views

### Cryptanalytic tests for biased nonces

In the paper Biased Nonce Sense: Lattice Attacks against Weak ECDSA Signatures in Cryptocurrencies on section 5.2 Cryptanalytic tests for biased nonces, one of test is: Select two signatures at ...
35 views

### Secret sharing by using just “private secrets”?

TLS is using 3 way handshake. Isn't that possible to use such 3 way handshake protocol to share a secret without using a public key scheme, for instance as follows: Let A, B be private secrets of ...
14 views

### Correctness and security of a scheme

Is correctness of a scheme considered part of the security of that scheme or is it separate? I've seen both approaches in different papers.
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### finding hash collisions for set of hashes

I am searching info on dependencies between different hash functions. Let's say that we have a set of x hashes H1, H2 ... Hn (using different hashing functions) of the same string S. For every hash we ...
15 views

### (Why) does unconditionally secure MPQC imply quantum bit commitment?

I have read in several papers now that information-theoretically secure multi-party quantum computation (MQPC) with a dishonest majority ($t \geq n/2$) is impossible because of the impossibility of ...
57 views

### Curve25519 Endianness

According to the original paper form Bernstein public/private keys and the shared symmetric key are stored in little-endian. However, the WolfSSL of WolfSSL supports both, little-endian and big-endian....
43 views

### Elgamal Encryption: Why does Bob get to reuse his keypair while Alice has to generate a new one for every message?

From Christof Paar's book The protocol consists of two phases, the classical DHKE (Steps a–f) which is followed by the message encryption and decryption (Steps g and h, respectively). Bob computes ...
27 views

### Why is confusion & diffusion not required PKI encryption schemes like Elgamal encryption?

The Elgamal encryption scheme is a Multiplicative Mask with the shared key. It doesn't seem to have any confusion or diffusion. So why is it not necessary here as compared to Block Ciphers?
26 views

### What are the strengths and weaknesses of this code - how to do it with stronger security [closed]

This fragment of python has come across to me for review, and I'm uncomfortable with it, but I don't feel I can enunciate what is wrong, beyond a vague statement that "it doesn't look like best ...
40 views

### Splitting Secret Key

If I split a key $k$ into three pieces as $k1, k2$ and $k3$ how should I distribute the keys among three people such that any two of them are able to evaluate PRF, but be secure from any one of them ...
16 views

### On the hardness of addition when the elements of a field is represented by the powers of generator and possible any existant scheme

We can represent elements of a finite field $F$ in various ways polynomial basis and normal basis. There is one other; generator-based representation and this is based on the fact that the ...
54 views

### Why this isn't a secure PRF?

Given that F is a secure PRF in the example $$F'(k,x)= F(k,x)\mathbin\|F(k,F(k,x))$$ I'm not sure why this isn't a secure PRF? Under what condition $F(k, F(k,x))$ when concatenated to $F(k,x)$ the ...
42 views

### How are m2 and m3 boxes computed?

I stumbled upon an AES implementation that uses boxes with multiples of 2 and 3 for its MixColumns operation. When inspecting the m2 box, I saw that the first line is : ...
38 views

### Ciphertext-only AES reduced rounds attack

I am trying to solve an AES reduced round attack exercise, I have a lot of AES encrypted strings encoded in hex in different files, I should answer which of these files is NOT encrypted with 4-rounds ...
29 views

### authentication by keyed hash function

assume i have: One-key cipher: E. Hash: H My application is authentication. I have a shared secret key with Bob for the One-key cipher. So, when I send an message to Bob, I also send an authentication ...
45 views

### In what paper was OCB2 introduced?

I've been working through "Cryptanalysis of OCB2: Attacks on Authenticity and Confidentiality" 1 from earlier this year. My knowledge of OCB2 is pretty shallow though, and so I'm keen to ...
46 views

### Proof that user public key corresponds the curve equation (secp256r1)

I'm currently stuck at a problem, where I'm supposed to proove that the user public key of a returned u2f token corresponds to an elliptic curve equation (secp256r1). The token looks as follows: ...
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180 views

### How to find the co-efficients of a function within Zp[x]?

I am a newbie in Finite Field arithmetic and while trying to implement an Elliptic Curve Cryptography based ABE scheme in a programming language, I am unable to understand how to implement function ...
23 views

### RSA decrypton correct? [closed]

Given $C_i$ = [176, 12, 64, 98, 185, 64, 98, 176, 138, 127, 45, 176, 35, 156, 138, 45, 45, 45, 98, 138, 104, 138, 51, 65, 138, 35, 168, 12, 22, 138, 176, 45, 12, 22] and $187, 3$ as public key. The ...
26 views

### Confusing Encryption Mode [duplicate]

I have an API that accepts plain-text and IV as input and I'm trying to identify the encryption mode for that API. I have already tested this API for ECB, CBC, OFB, CFB and CTR and it doesn't seem to ...
15 views

### Spontaneous parametric down-conversion

we generate heralded single pho- tons via spontaneous parametric downconversion using a 5 mm long periodically-poled potassium titanyl phosphate (ppKTP) crystal pumped with a 405 nm diode laser (200 ...
52 views

### How to prove document ownership at a specific time [duplicate]

Problem Given any piece of data, I could sign it with public key and made available online. This proves I am in possession of given data, but it doesn't tell I am the creator. The only possibility (I'...
33 views

### Converting a plaintext to hex for AES encryption

Looking through AES process I see it uses a substitution table which need the input in the form of hex. Im wondering if i have a plaintext of 16 bytes such as 'j±…<Ãà!DÈ¶;5˜‰*', how can I convert ...
33 views

### How to alter text that was encrypted with AES CBC using PKCSPadding7

Assuming, I had a ciphertext along with its decrypted plain text result but not the IV or the Secret Key. (keep in mind that the text was encrypted with AES/CBC/PKCSPadding7). How would I go about ...
15 views

### How Bob detect the Eve in QKD BB84 protocol

1- how is eve have access to quantum channel? How bob will know there is eyedropper? 2-what is different between quantum channel and classical channel?
28 views

### Issue with only applying key addition layer before first round of AES

What would be the issue if AES only applied the key addition layer once, before the first round? As in, how would this make the algorithm vulnerable to attack?
26 views

### how to verify the digital signature in a zero knowledge proof

I know that the zero knowledge proof is able to prove to the verifier that the holder does in fact posess the digital signature issued from an issuing 3rd party but... How does the verifier validate ...
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### Criteria for public modulus of RSA accumulator

What are criteria for generation of an RSA public modulus used in an RSA accumulator, and their rationale? Are there special requirements in some sub-cases, like for «one-way» accumulators? Josh ...
51 views

### Why mounting/dismounting an encrypted file container takes only a few seconds?

When the encrypted file container contains 100000 files and 500 GB of data, all of them must be decrypted/encrypted when the container is mounted/dismounted. How can Truecrypt/Veracrypt perform this ...
28 views

### Are there any universal PRG’s or PRF’s?

Leonid Levin constructed a universal one-way function, i.e. a function $f$ such that if any one-way functions exist, then $f$ is a one-way function. My question is, what universal pseudorandom ...
11 views

### Security of LWE when a small leakage is allowed on the noise

Short version: Is there some results that are known on the security of the Learning With Error problem when there are some leakages, notably on the noise? (In my case these leakage come from a bit ...

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