All Questions

79 views

A confusion about linear span of modified de Bruijn sequence

Recently i'm reading "Cryptographically Strong de Bruijn Sequences with Large Periods" . In the section 2 2.1 Basic Denitions and Properties , property 1 says that ...
134 views

When do I need to renew keys for Salsa20 or HMAC?

I currently have a system which uses two keys sourced from a single key subjected to HKDF. One key is used in the Salsa20 stream ...
159 views

Rabin/RSA four possible messages?

Given this encryption method: $$f_{N,e} : Z^{*}_{N} \to QR(N)^{*};\quad f_{N,e}(x) = x ^{2e} \bmod N$$ I need to show that, for any $x_{0} \in Z^{*}_{N}$, there are four elements $x \in Z^{*}_{N}$ ...
60 views

Can you clarify the proof that secure LR-two party protocols do not exist?

In the paper “Multiparty Computation Secure Against Continual Memory Leakage” on pg. 1237, the footnote #1 discuss why it is not possible to construct a leakage resilient two-party protocol. But I'm ...
166 views

Design requirements for a keyed hash function?

I am actually preparing for a cryptography exam, and I found a question asked by the professor in the class, below are the lines that I copied from the slide : Example: Let $Ek$ be the encryption ...
289 views

Bit commitment with 1-out-of-2 oblivious transfer

I know a protocol for bit commitment using regular OT (Bob has 1/2 chance of learning the bit Alice transferred to him) which goes like this: COMMITMENT PHASE Alice chooses a bit $b$ For ...
93 views

how to truncate a PRF on n bits to PRF on t bits where t < n? [closed]

Dan Boneh's courersa lecture on format preserving encryption at 5.50 mins , talks about truncating a PRF on $n$ bits to PRF on $t$ bits. The approach is by appending $(n-t)$ zeros to input $t$ bits ...
318 views

Bellovin 96' attack on IPsec ESP protocol on encryption only option

Can you explain the actual attack? Why does the attacker need to firstly send some arbitrary UDP packet? How can the attacker break the privacy between A and B? Link: The article of Bellovin I'm ...
106 views

Are there public $p$ and $q$ numbers for use in DSA?

There are many RFC documents giving large primes to use in Diffie-Hellman. However, I couldn't find standards on the $p$ and $q$ large primes used in the DSA signature scheme. This is proving to be a ...
161 views

71 views

Any functioning system for interactive proof?

My problem is to outsource an array of data and ask the prover to sort the data. I am wonder if there is any working system out there that support interactive proof for the above computation? Or if ...
67 views

Protocol/algorithms based on a variable-length input PRF

Are the proofs based on a PRF assumption still valid when using a variable-length input PRF ? The answer might be obvious, but I have a doubt.
123 views

Cryptanalysis not based on method used to encrypt? [closed]

When doing cryptanalysis on RSA or something number theory based, there are various attacks that all seem to involve number theory (Wikipedia: RSA_(algorithm) ~ Attacks_against_plain_RSA). Similarly, ...
430 views

Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? [closed]

Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? I know you can, of course, use a 4096 bit key for your server certificate, but I usually see 2048 bit ...
819 views

How do I enable AES-NI (hardware acceleration) for Node.js crypto on Linux? [closed]

I wrote a basic function to test the speed of the AES-256-CBC mode of the Node.js built-in crypto functions. These functions use OpenSSL, so they should support AES-NI, but when I correctly enable ...
155 views

How many messages needs to be send to server to get AES key in Cache-timing Attack

I'm trying to evaluate the correlation between key length and the number of messages that needs to be send to server during Cache timing Attack. I read both D. Bernstein, “Cache-timing attacks on ...
575 views

Question about modifying the MD5 plain text to cause a collision

I was trying to understand MD5 and got stuck with this question, its from Michael sipser's book on Information security Principles and Practice, 2nd edition The MD5 collision in Problem 25 is said ...
32 views

I'm trying to understand the framework of reactive simulatability using *"PfWa2_00AsyncModel"* from this publication which is a tech report behind the paper A model for Asynchronous Reactive Systems ...
311 views

How to perform benchmark of block/stream ciphers?

I would like to perform some benchmarking of different block and stream ciphers for general data (lossless and lossy data) encryption and decryption (with focus on power consumption). To get general ...
93 views

Can you help me understand this “Message Modiﬁcation by Meet-in-the-Middle” related to Tiger Hash? [closed]

I found this paper that explains how to attack a reduced round tiger hash, but I'm having a hard time understanding some of the mathematical notation. Could someone explain the section "Message ...
182 views

After looking at this security issue at DjangoProject, I started to think in a password-based authentication that places the burden of PBKDF2 (or whatever is the hashing function) on the client. So I ...
342 views

How does identification currently work with the German identity card? [closed]

Since 18th of December 2010 Germany makes use of an identity card that should allow electronic authentication: (image source: commons.wikipedia.org) From a users perspective, the authentication ...
92 views

partial-domain permutation and strong assumption

Quoting "Verified Security of Redundancy-Free Encryption from Rabin and RSA", Chapter 2 (on page 4): OAEP was proved IND-CCA-secure by Fujisaki et al. [28] under the assumption that the underlying ...
86 views

169 views

Security of a 3-party key exchange protocol

I am trying to find attacks on a theoretical protocol or prove its security. An initiator wants to establish a shared key with a responder with help of a trusted server. We have the following roles: ...
115 views

Jumblar: Using map locations as passwords

I had the idea of converting map locations into passwords. Basically Jumblar takes a hash of the user's location and stores this as a comment on the PGP network. The 'stored-hash'(Vague-Hash) ...
97 views

BLS signatures in the G-valued Random Oracle Model

This paper on semi-generic algorithms considers "non-standard properties of the employed hash function". For BLS signatures whose main group is $G$, I'm curious what can be shown when the hash ...
139 views

Ideal system for an encryption scheme

What is the ideal system for an encryption scheme? For a pseudorandom permutation the ideal one is a random permutation, for a pseudorandom function the ideal one is a random function. For an ...
101 views

Is this any recognizable encoding or cipher? [closed]

I've been watching the Marble Hornets videos on YouTube (basically, an independent film series about a group of kids chased by the "Slender Man"), and in this video I saw something interesting. ...
131 views

Is it possible to derive the midstate of a sha256 hash?

Let's say I have an unknown string with the known sha256-hash of it. I was wondering if it was possible to now calculate the sha256 of the concatenation of the unknown string and "abc". (In PHP: ...
164 views

Complex Numbers on Elliptic Curves & Usage in Tate Pairing

I'm working with understanding the internals of the Tate Pairing. I was going through an example of the curve $E: y^2 = x^3 + 3x$ over $\mathbb{F_{11}}$. The author is showing the computation of ...
127 views

How well analyzed are giant block length ciphers?

I have heard about ciphers that have a block length of 256 megabytes... That is huge. How well are they understood by the encryption community? I'm referring to PMC Ciphers. Has anyone used such a ...
99 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 $\hat{m}=mS$ ...
389 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 ...
140 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 ...
180 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 ...
94 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 ...
82 views

Predicate Encryption supporting disjunctions

I am not sure if I missed some subtlety in the definition of Attribute Hiding found in this paper on Predicate Encryption, but isn't it possible to construct a scheme for Predicate Encryption ...
28 views

Encryption with Deduplication [duplicate]

Suppose I have a file server running ZFS with file deduplication enabled, and I have two users that are sharing files: Alice and Carol. If Alice uploads huge_file.tgz to her www/ directory, and Carol ...
270 views

One-time pad and perfect secrecy properties

I have a homework problem: Explain how to find $m_{0}$ and $c$ such that $P[c=c': k \leftarrow K, c' \leftarrow E(k, m_{0})] > 0$ where P is probability and k is chosen uniformly. I do not know ...
149 views

How hard is a known prefix hash preimage attack?

Suppose the attacker knows $X, Z$ such that $H(X || Y) = Z$ If bit-length(Y) < 60 then a brute force attack is possible. What if ...
99 views

Prevent/minimize replay attacks in public message board

Assume we have a public message board where anyone can send a message to. If plain messages are used, anyone can impersonate anyone. The goal is to disallow impersonations. We can use public key ...
255 views

Creating colliding x509 certificates: Crafting RSA moduli step

I am trying to generate 2 x509 certificates with the same signature but different values in the common name field, based on md5 collisions, as it was specified in this paper (page 7). Now I have ...
218 views

elgamal based decryption mixnet

Can anybody help me to understand elgamal based decryption mixnet? Pure elgamal can be used in mixnet (re-encryption mixnet) and its very easy, and I have implemented decryption mixnet using RSA also. ...
181 views

Why not use CBC, not send IV, and assume first plaintext block is garbage? [duplicate]

Possible Duplicate: Using CBC with fixed IV Forgive me if this has been asked before, I looked but haven't seen any answers that suit. Is there any danger in using CBC, encrypting a ...
40 views

Will length-extension work if secret is not prefixed but appended to the data? [duplicate]

Possible Duplicate: Why is h(m||k) insecure? Length-extension allows to append any data to the message while not knowing the secret. Any length-extension explaination one the web considers ...
649 views

Determining the algorithm used to generate a digital signature

I have a string "abcd pqrs". This string is digitally signed with an X.509 certificate (with its private key) and it produces a signature. From the signed string, is it possible to find out what ...
I have some questions from previous years exams, I hope you could help me with them. :) Suppose that a protocol satisfies the properties of a $\Sigma$-protocol, except that it is only (plain) ...