# All Questions

2k views

### What is “Implicit Authentication”?

What is “Implicit Authentication” in the context of authentication methods? I searched the Web but could not find any article that describes this. If anyone can describe it, that would be a great ...
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### How does PBKDF1 work?

I need some basic guideline on Password Based Key Derivation Function. PBKDF1 generates a key from password and salt using Hashing algorithm (like SHA1, SHA256, MD5). What is the step behind this?
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### How to construct encrypted functions (with either public or private data)?

Homomorphic encryption is often touted for its ability to Compute on encrypted data with public functions Compute an encrypted function on public (or private) data I feel I have a good grasp of #1 ...
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### Use of q-ary lattices in developing cryptosystems

Why q-ary lattices are used to most cryptosystems rather than lattices. In most of the papers q-ary lattices are used. Is there any advantage? and Given $$B=(v_1,v_2,v_3,.....v_n)$$ is the basis, ...
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### apprSVP in lattices

The approximate Shortest Vector Problem (apprSVP) is a problem where, given the basis and the approximation factor $\gamma$ (a function of the dimension $n$), one must find a vector $v$ belonging to ...
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### Why can ssh-keygen export a public key in PEM PKCS8 format?

In the documentation of ssh-keygen (man ssh-keygen) it says for the option -m that an export ...
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### How hard is the Solitaire cipher to crack?

Assuming your deck is completely random and that it is not retrivable, how hard would it be for a casual person to decrypt a message encrypted with the Solitaire cipher?
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### AES storing the length within the encrypted data versus storing it outside

I need to strip off padding after decrypting AES(CBC)-encrypted data (I have control over encryption and data transmission), so have looked at adding the length of the original data to the payload ...
118 views

### Deterministic ECDSA signatures?

ECDSA signatures depend on parameter k that is chosen by the signer. As a result, there are many signatures for the same private key d and message m. What I want to achieve is a deterministic ...
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### Why is the re-encryption algorithm in Universal Re-encryption for Mixnets more complicated than apparently necessary?

This is the paper. On page 6, the paper describes a variant of El Gamal and a way of re-encrypting ciphertexts. I thought an easier way to do encryption is to output $(m(g^x)^y,g^y)$, and universal ...
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### Inserting a backdoor into a cryptographic hash function

I'm curious as to how a backdoor can be built into a hash function. What might it take the form of? What's probability of getting one that can be backdoored in a way that can actually undermine its ...
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### Is the reduction from left-or-right IND-CPA to real-or-random IND-CPA tight?

A modern trend in cryptography consists of defining security as rigorously as possible, and then designing schemes which are secure according to those definitions. Proving security comes in the form ...
2k views

### AES GCM vs other encryption modes in embedded environment for network traffic

I'm doing a lot of research since I'm doing an internship for a company where I need to upgrade their security level. Their own protocol needs a cryptographic upgrade and I'm leaning towards AES since ...
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### Isn't the security of EC curve 25519 126 bits?

The security of the EC25519 is given as 128 bits, but since the order of the group is 252 bits shouldn't the security be 126 bits? Given as half the magnitude of the underlying field, since DLP ...
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### PBKDF vs HKDF for pretty long key

I'm developing a messenger application with encrypted chats. In the first version of the app I've used PBKDF2 (10000 iterations, SHA1, random salt) to extend a short user password and generate keys ...
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### Does RSA operate over a Finite Field (Galois Field)?

Is it correct to say that RSA operates over a Finite Field (Galois Field)? In this case GF(p)? I do understant that the modulo in RSA is not itself a prime number, but all the operations ...
187 views

### Why does NTRUEncrypt lack a formal security proof?

Is there any particular reason why NTRUEncrypt lacks a formal security proof? That is, a demonstration that it achieves certain security notion (e.g. IND-CPA). I know there is a provable-secure ...
955 views

### ZIP 2.0 encryption bruteforce attack

I have an old sourcecode backup from my DOS days stored in a ZIP 2.0 encrypted archive, but I lost the password. The password was written on a paper slip, but I remember that it consisted of 30+ ...
213 views

### Adding tweak to a block cipher

I know there are XEX, XTS and other ways to add tweak to block cipher without modifying cipher itself. However they are quite slow and/or complex. If we assume we have a secure block cipher round ...
161 views

### Compression function to guarantee randomness of one time pads?

First of all, I would like to note that I am not building my own crypto. I am simply curious and would like to learn. What I am wondering is this: if we are worried about randomness of something ...
540 views

### True Random Number Generator by milliseconds per keystroke (TRNG-Kms)

The simplest way to generate truly random numbers for OTP keys is to measure the time in milliseconds between each keystroke on a keyboard. The randomness depends on the user typing in various speeds. ...
105 views

### Turning PRPs in PRGs with a counter

I am following the Coursera Cryptography I course and I have the following question, I am a bit perplexed by the statement, in week 2 lecture "What are block cyphers?" that a counter-mode PRF is a ...
133 views

### Advantages of making streamcipher stream depend on plaintext?

Most descriptions that explain how streamciphers work (like the one on Wikipedia), tend to describe a model that boils down to a simple “$ciphertext = plaintext \oplus stream$”, where the stream is ...
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### Use cases for “online” authenticated encryption?

What is the the point of an "online" mode for an authenticated cipher? I understand what "online" means in this context. However, I have trouble coming up with applications that would benefit from ...
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### MARS and RC6 in CUDA

I am working on a project where I am benchmarking the 5 AES finalists (Rijndael, Twofish, Serpent, MARS and RC6) on CUDA Hardware. My problem is that I am no experienced CUDA programmer. My approach ...
269 views

### Random session key + predictable IV

I'm using Blowfish in a toy Diffie-Hellman communications scheme. Random session keys are generated for each connection. In this case I can simply feed a null array to the IV right? The same ...
317 views

### Why no swapping block in the last round of DES?

Round 16 on the encryption side, and round 16 on the decryption side of DES have no swapping module. Why is it like this? Can anyone provide any justification? This is my homework question.
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### OMAC/CMAC constant for different block sizes

OMAC/CMAC only specifies constants for 64-bit (0x1B) and 128-bit (0x87) block size. I would like to know how to get constants ...
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### Is there any research about cryptography on nondeterministic Turing machines?

I know it's a highly theoretical topic, but I was wondering if there was any research out there about what cryptography would be like assuming that we had access to nondeterministic Turing machines. ...
302 views

### Is this method of deterministically using CBC secure?

I'm trying to design a deterministic encryption scheme to enable searching in untrusted databases with the smallest possible IV overhead on ciphertexts. I know it's very bad practice but unfortunately ...