All Questions

17
votes
1answer
976 views

Should I trust CipherCloud? [closed]

Should I trust CipherCloud's system for "homomorphic encryption" of data in the cloud? Has the security of their system been subject to peer review or other cryptanalysis? Is there any known analysis ...
5
votes
2answers
920 views

Is encrypting a single 128 bit block with AES ECB “safe”

I want to encrypt a small piece of data that is less that 16 bytes in size (think SSN), and I'll be using a 256bit encryption key. The typical suggestion is to never use ECB, but if there is just a ...
1
vote
1answer
102 views

How to learn the first bit of m in padded RSA

Consider the following version of padded RSA encryption, where encryption of $m$ is done by setting $m′ = (0^k~||~r~||~00000000~||~m)$ for a random $r$ (of length 8 btyes = 64 bits) and then computing ...
1
vote
1answer
1k views

AES AddRoundKey

Looking at the first step of AES encryption I see that we XOR the key with the plaintext block. Why is the actual key involved at all, why not just use the round keys derived from the key schedule?
3
votes
2answers
390 views

What is the best way to store sensitive information on the client?

I am very inexperienced with cryptography and would like some advice on how to store some sensitive information on client machines. I have some information stored in a central database on my server. ...
2
votes
1answer
180 views

Can prepending “junk” be equivalent to an IV when encrypting using CBC?

We are encrypting a small positive integer (1-1000) with a constant key using AES256 encryption. We are considering two approaches to make this secure; use an initial vector (which we then need to ...
2
votes
0answers
79 views

PKC McEliece + $S$ + $P$ [closed]

I am trying implement the McEliece crytosystem in SAGE. My question is How I will be able to choose the appropriate matrix $S$ and $P$?. I ask this because when I trying obtain the vector $\hat{m}=mS$ ...
3
votes
2answers
169 views

GPG and PAR2 error correction data from the plain archive, will it compromise security?

I have the following scenario: Archives compressed with 7z, hundreds of MiB in size GPG to encrypt the archives (binary, without ASCII armor) PAR2 to create error correction data Question 1. ...
8
votes
1answer
2k views

How can scrypt be improved to counter GPU mining

I know scrypt was designed to lessen the GPU/ASIC advantage. We now have litecoin as a real-world example of this. However, it hasn't worked out perfectly. Most coins are mined by GPUs, although the ...
1
vote
2answers
203 views

How secure is passing a MAC to Python's random.seed before using random.choice to generate a MAC?

I'd like to use Python's random.choice seeded with a HMAC-SHA1 tag to generate a MAC encoded in a variable set of chars. ...
3
votes
1answer
637 views

Why are the Davies-Meyer and Miyaguchi-Preneel constructions secure?

The Davies-Meyer compression function $h(H, m) = E_m(H) \oplus H$ is said to be secure. So too is the Miyaguchi-Preneel compression function $h(H, m) = E_m(H) \oplus m \oplus H$. Why are these ...
2
votes
2answers
283 views

Why is $h(H, m) = E(m, H) \oplus m$ insecure?

I am taking a cryptography class on Coursera. I learned that the compression function $h(H, m) = E_m(H) \oplus m$ is insecure (even though other variants like Davies­-Meyer or Miyaguchi-Preneel are ...
5
votes
1answer
306 views

In textbook RSA with low public exponent, how big does a random message needs to be?

Assume RSA with a public modulus $N$ of $n$ bits, a small odd public exponent $e$, plaintext $M$ a random non-negative integer less than $2^m$ for some integer parameter $m$, with $M\mapsto C=M^e\bmod ...
2
votes
1answer
213 views

What's the probable usage of Interlock Protocol

I've recently read some articles about the Interlock Protocol, Article by Ron Rivest and Adi Shamir. I'm wondering if it is possible to protect Key-exchange under Public-Key cryptography from the ...
8
votes
1answer
3k views

Why exactly is Blowfish faster than AES?

I've not been able to understand exactly the reason behind Blowfish being faster than AES. Is it dependent on the block size? Or is it processor dependent? (if Yes, then lets assume that AES ...
0
votes
1answer
437 views

Ciphertext-only attack on Simplified DES

Is it possible to deduce the plaintext block or the key, given only a Simplified-DES ciphertext block (e.g. c=01110110)? I'm reading Cryptography And Network Security, by William Stallings and I'm bit ...
4
votes
1answer
188 views

Is it safe to assume Salsa20 to be a PRP?

Often in security proofs a certain block cipher is assumed to be a pseudorandom permutation or PRP. I wonder if this goes for stream ciphers as well, and specifically for Salsa20. If limit ourselves ...
2
votes
2answers
768 views

Keys required for cryptography

I am reading an article on cryptography at following location: http://www.entrust.com/resources/pdf/cryptointro.pdf Historically, encryption systems used what is known as symmetric cryptography. ...
1
vote
2answers
408 views

Does key authentication in SSH protect from MitM?

How do cryptography in SSH(2) work (secure channel establishment, authentication)? Does key authentication in SSH(2) protect from MitM by providing authentication and integrity and why?
1
vote
0answers
128 views

Perfect secrecy and change of plaintext probability distributions

How to prove that if a cryptosystem has perfect secrecy for a given plaintext probability distribution then it will have perfect secrecy for all other possible plaintext probability distributions? Do ...
1
vote
0answers
41 views

Encrypted Functions with Fully Homomorphic Encryption [duplicate]

While Fully Homomorphic Encryption schemes facilitate carrying out computations over encrypted data, can the function that has to be evaluated be encrypted too ? For example, if i have some programs ...
6
votes
1answer
507 views

Correct way to map random number to defined range?

Say that we have a secure random number generation that outputs 32 bit random numbers, so it's output is a true random number between 0 and a MAX. What is the best way to map this random number to a ...
2
votes
0answers
139 views

Correct way to truncate data to a range [duplicate]

2 hours ago I thought I had this figured out, but now I am doubting myself and want someone to validate my algorithm. I want to take a stream of k trusted random ...
1
vote
1answer
2k views

decryption many time pad [duplicate]

I have eleven ciphertexts that were encrypted with the same key (which I don't know). I want to decrypt the last ciphertext. I read similar question like Many time pad attack but I can't solve my ...
2
votes
0answers
149 views

How can I prove that this encryption scheme from a random oracle is secure?

I am reading this example: A random oracle is an ideal object. What makes a random oracle convenient for proofs is the part about knowing nothing on the output for a given input if you do not ...
2
votes
1answer
65 views

Comprehension question on a signature protocol based on the RSA assumption

We have the following two-party protocol between Alice and Bob. Alice sends messages $m_1, m_2, \ldots \in_R \mathbb{Z}_n^*$ to Bob and Bob signs these values by calculating $v_1, v_2, \ldots \in_R ...
3
votes
1answer
194 views

How to use salt if I am sending hashed password?

If have application that is sending username and hashed password to server for authentication, how would I use salt for this scenario ?
1
vote
2answers
230 views

ElGamal: Generation of “g” value?

I haven't been able to find a clear explanation on this (and I'm probably just confused in general). I have the following parameters of ElGamal signatures: $p$ = safe prime $q = (p-1)/2$ $g$ = an ...
5
votes
1answer
211 views

Is there an existing AEAD scheme with minimal IV requirements?

Is there an existing AEAD scheme such that, for inputs with the same AD and IV ciphertexts are allowed to leak whether or not their plaintexts are equal, if the scheme can process the plaintext in a ...
1
vote
1answer
102 views

Pseudo Random Generator (PRG) from Rabin function

I'm trying to make a PRG using the Rabin function. The code (in Java) I wrote to implement the function is: ...
1
vote
1answer
479 views

Proper uses for CTR and CBC AES block cipher modes

Assuming the following: Key is randomly generated is being used (32 bytes+) IV is also randomly generated Crypto random key generator is used Data being encrypted contains common bytes like ...
2
votes
1answer
92 views

Why unit vectors should be encrypted bit per bit in that case?

At this work at section $2.2$ concerning a possible application for the BGN cryposystem the author points out that if you want to encrypt a unit vector $\overrightarrow{u_l}$ of size $l$ then the ...
2
votes
0answers
75 views

Relaxed trust criterion for mental poker server?

I've read a lot about protocols for mental poker without a trusted server, but I'm interested in the possibility of a faster, more practical protocol that relaxes that criterion a bit and "trusts" a ...
2
votes
1answer
85 views

What does “adaptively secure” mean?

In a paper it says "In the generic group model, the PRF is adaptively secure for inputs of $\mathbb{Z}_q^n$". Maybe a stupid question, but what does "adaptively secure" mean exactly?
2
votes
3answers
180 views

EC equivalent for RSA-OAEP

I have some questions regarding aforementioned subject: Is there a EC equivalent of RSA-OAEP key transport/encryption algorithm ? Is ECIES-KEM sufficient ?
1
vote
1answer
136 views

AES Message Authentication Vulnerability

My securities instructor recently posed this question to the class and I am bending my brain in half trying to figure it out. Suppose $y_1 = AES(K, x_1)$ and $y_2 = AES(K,x_2)$, and suppose you ...
1
vote
1answer
179 views

ECKS-PS algorithm: searching in encrypted data; bilinear maps

I have found an encryption algorithm named ECKS-PS (published in the paper Efficient conjunctive keyword search on encrypted data storage system) that allows an user to search in encrypted data. All ...
6
votes
1answer
309 views

Any point in waiting for the SHA-3 standard?

The Wikipedia article on SHA-3 says that Keccak has been chosen but the standard hasn't been issued. Does this matter? That is, can we just assume it's going to be as specified by the submitters ...
6
votes
1answer
154 views

What's the state of the attack to get the first pre-image on MD4?

What's the state of the attack to get the first pre-image on MD4? Is it still $2^{102}$ as described by Gaëtan Leurent in "MD4 is Not One-Way" ?
2
votes
2answers
3k views

AES+CTR+HMAC Encryption and Authentication on an Arduino

In my project we would like to encrypt and authenticate the the communication channel between our server and our Arduino nodes, which relies on an underlying TCP channel. We have chosen AES in CTR ...
1
vote
2answers
273 views

Using salted hash as password for easy memorization without reuse?

I had an idea earlier: Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a key between sites, and include the site's name as a salt? For example: ...
3
votes
3answers
217 views

Ciphers in CBC mode reveal place of change in plaintext

Theoretically, when using a symmetric block cipher in CBC mode, the current block is dependent on the previous block. Suppose one plaintext is encrypted using CBC, and then one bit of it is changed, ...
4
votes
2answers
466 views

Signature schemes for underpowered devices (8bit microcontroller)

I am currently researching into a small scale home automation system, aiming for cost. The system architecture is basically one master and several slaves which are connected in parallel. Recently ...
3
votes
2answers
916 views

Known-plaintext attack on Blowfish in ECB mode

The protection scheme I faced recently seems so weak nowadays that a simple exhaustive key search would be enough to recover the user key in an acceptable amount of time (it's OK, since almost no ...
1
vote
1answer
140 views

Given a certain entrophy per character, how long should a passphrase be to guarantee key strength?

Given an entrophy of 1.5 bits per character, how long does a passphrase have the be to guarantee a key strength of a 128 bit random key? Assuming an alphabet of 26, one character takes log2(26)=4.7 ...
-1
votes
2answers
366 views

May the problem with DES using OFB mode be generalized for all feistel ciphers

There is a problem with using DES as the block cipher in OFB mode, eg: the feedback that goes back into the next round will be encrypted with the same key $k$ resulting back into the plaintext IV used ...
4
votes
1answer
4k views

Does the IV need to be known by AES (CBC mode)?

I was thinking about this today and thought I should ask. I think I understand IV's enough to say that they are basically the same thing as Salts when talking about hashes. They are there to improve ...
1
vote
0answers
312 views

How do I generate decryption keys for the IDEA algorithm from the 128 bit key?

I am trying to implement IDEA algorithm in C#, just to learn how it works. I have taken a 128 bit binary key and generated the 52 encryption keys using the following code: ...
0
votes
1answer
70 views

PBKDF2 when dkLen and hLen have the same size

I was reading RFC 2898 and something is not clear to me. When I use PBKDF2 with SHA-256 and I want a derived key with length 32 bytes (the same length as my hash function output), your derived key ...
2
votes
1answer
595 views

Question about the definition of a secure PRF

I'm taking a cryptography introduction course, and we're covering the definition of a secure PRF. I understand the test goes as follows: A challenger picks a function $f$ such that $f \leftarrow ...

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