# All Questions

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### Efficiency of finding sub group order vs factorization

Suppose you got a prime $p = 2\mathbb\Pi_{i=0}^{n-1}q_i+1$, where $2^{k-1} \lt q_i \lt 2^k$ for some $k$ and all $0 \le i \lt n$, and that you also got a generator $g$ of one of the prime order sub ...
123 views

### Secure Sketch Construction

I would like a user to choose a point on an image which is represented by (x,y). This is meant to be a security token. When a user uses this location to login they are unlikely to to choose the exact ...
272 views

### Quadratic residuosity problem reduction to integer factorization

How can one show how to reduce the quadratic residuosity problem to an integer factorization?
716 views

### Encrypted counter as IV in CBC mode encryption using same key

I'm currently working with a secure transport protocol that defines the IV to be a counter (incremental nonce) to be encrypted with the same key. This is a followup to a protocol that did not provide ...
174 views

37 views

### What information should I send along with an AES ciphertext and is there any standard to do that?

While using some crypto implementations I got to see that many times a comment is added to the ciphertext. For example: ...
363 views

### Is XOR adequate for encrypting truly random data? [duplicate]

It is well-known that the two-time pad is very insecure. However, it seems unexploitable in the case where the plaintext is indistinguishable from random (ex. symmetric keys). Is this property ...
109 views

### Are there any successful preimage attacks?

Are there any successful preimage attacks on any serious cryptographic hash algorithm or at least on serious-looking non-cryptographic hashes (like MurmurHash)?
48 views

### Faster alternative to HKDF

HKDF is used in one of my projects to derive separate keys from a common master key. But profiling has shown it to be the performance bottleneck under certain circumstances. Is there any faster ...
183 views

Considering the following encryption scheme where RSA is used to encrypt a plaintext m and then we choose a random r and compute: $$A = r + m^e \bmod N$$ and $$B = r^e \bmod N$$ So the ciphertext is ...
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### Would SHA-1 be safe for certificates with short validity?

There are articles floating around the topic of SHA-1 deprecation. The gist of it is that in (mostly) developing countries, people are still using mobile/computing devices that are 5 years old (or ...
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### Truncating ciphertexts on ring-LWE schemes

On the section 5.4 of the paper Improved Security for a Ring-Based Fully Homomorphic Encryption Scheme, the authors explain how to discard some bits of the ciphertexts to get smaller ciphertexts and ...
112 views

### secure PRF or not

I am new in Cryptography and I saw this question in a note I solved it but I'm not sure about my answers. Let $F : \{0, 1\}^n × \{0, 1\}^n→ \{0, 1\}^n$ be a secure PRF (i.e. a PRF where the key ...
83 views

### Why can you reverse a modulo function when knowing its primes

We are dealing with cryptography in school right now and superficially went over the Rabin cryptosystem with the (apparently usual) example of p=7 and q=11 etc (we didn't do RSA). I understand that ...