# All Questions

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### Are there some well-known crypto APIs that leak information?

Are there any well-known crypto APIs or libraries that leak or used to leak information (it can be the key or anything else)?
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### Calculating 3DES Key Check Value (KCV)

I am trying to verify a Triple DES Key Component generated by PC Crypto. The key portion is: E6F1081FEA4C402CC192B65DE367EC3E and the KCV value that should be ...
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### Order-Preserving Encryption (OPE) and leakage

I recently came across OPE and Order-Revealing Encryption (ORE), but I didn't exactly got the idea why they are important. What's exactly important about them? Are they actually used in practice? My ...
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### SAT-Based Public Key Cryptosystem

I am researching post quantum cryptography and I've stumbled upon this article which presents a PKC with an np-complete (SAT) trapdoor. I was wondering if someone could help me understand the way the ...
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### Is this an effective obfuscation technique?

Long ago I created a simple program which obfuscated a file by taking the first byte, then XORing it with the second, taking the (original) 2nd byte and X-ORing with the 3rd, etc, down the line. The ...
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### Can Shannon's entropy be used to determine if a file is encrypted?

If we have to determine a file is encrypted or not, can we use Shannon's entropy algorithm on the file? As discussed here, the entropy (in bits per byte) being closer to 0 is considered as more ...
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### Can a hash have more than one input?

From a definition stand point, can a hashing algorithm have more than one input, ex: $H(m_1, m_2, m_3)$? If not why are algorithms like bcrypt, scrypt and pbkdf2 referred to as password hashing ...
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### HSM RNG - Compliance to FIPS 186-2

If the RNG of a HSM is said to be compliant to FIPS 140-2 (approved DRBG - SP 800-90 CTR mode) does also imply that it is compliant to FIPS 186-2 ?
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### If I send a signed email, how does the end user get the public key?

I am sending a signed email using Python and smtplib. I have successfully signed the email using this example: http://proj.badc.rl.ac.uk/svn/ndg-security/branches/Dependencies/m2crypto/doc/howto.smime....
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### How to meter and limit number of files encrypted?

First my apologies if this isn't the right forum for this but here's my problem : I have a black box that takes an input file and produces an output file. I want to sell this black box to a customer ...
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### In which situation is HMAC mandatory rather than signature?

I’ve seen that the question has been asked already but this is still confusing to me. In a digital signature, Alice sends a message M and the ...
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### If I encrypt data with two different ECC Private keys, how secure is the result?

I'm wondering whether encrypting data with two different 256-bit ECC keys will result in a more secure encryption (minimum 384 bit equivalent) or will result in data that's effectively encrypted with ...
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### Encoding an element in $r=r'||h(r')$ way

We consider a finite field $\mathbb{F}_p$, where $p$ is a large prime e.g. 256-bit. We have $b$ a fixed element of the field. We encode it as $b'=b||h(b)$, where $h(.)$ is a cryptographic hash ...
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### What is entropy?

We discuss a lot of topics and use measures of entropy to determine how difficult it is for an attacker to be successful. What does entropy mean in the context of cryptography? How is entropy ...
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### Homomorphic encryption implementation over circuits or assembly code [on hold]

I've looked at a few implementation of homomorphic encryption, such as HElib, but they only consider additions/multiplications and such. Is anyone aware of any implementation of homomorphic ...
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### Entropy of Hash function [duplicate]

How is the entropy of the output of hash functions are defined? More specifically I saw in the paper https://eprint.iacr.org/2013/383.pdf Table 3 page 24. The entropy of challenge is mentioned which ...
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### Which public key cryptosystems are not based on number theory?

Are there any public key cryptographic systems whose hardness assumptions don't involve number theoretic problems?
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### Security of basic SHA256 MAC in an authenticate-then-encrypt scheme

I know the following construct is insecure if the MAC as defined below is appended to the encrypted message in an Encrypt then Authenticate (EtA) scheme. $k_1$: encryption key $k_2$: authentication ...
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### We can obtain “absolutely perfect CONFIDENTIALITY” using the one-time pad. Is there such a thing as “absolutely perfect INTEGRITY”? [duplicate]

The OTP (one-time pad) gives us perfect secrecy. This is the very best confidentiality available in this universe. (Although it does require large keys, which is beside the point of this question). ...
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### any post-shannon symmetric ciphers?

As far as I understand block ciphers use only simple operations to ensure good enough confusion and diffusion levels. meaning there is no math in it. "breaking a good cipher should require as much ...
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### Calculating Polynomial Inverse with extended euclid in java

I'm trying to understand the NTRU-PKCS and therefor I wanted to code a naive Version of it. Now my Problem: I tried to calculate the inverse of a Polynomial with an extended Version of euclids ...