# All Questions

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### Can keys from Bitcoin's Hierarchical Deterministic Wallets be correlated (reducing privacy)?

I'm trying to understand if the feature "Hierarchical Deterministic Wallets" in Bitcoin allows for complete privacy of all derived keys, and if any of those keys can be associated with each other ...
57 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.
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### What role plays Quantum Fourier Transformation in Shor's integer factorization algorithm?

I cannot seem to understand the role or goal of Quantum Fourier Transformation in Shor's integer factorization algorithm. Is it used to collapse all quantum states into one, in which it has a factor ...
187 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 ...
30 views

### Detail about reactive simulatability framework

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 ...
126 views

### Precise meaning of various terms related to universal hash functions

I've been reading about universal hashing, but I'm confused by all these different terms and notations. Could someone help me understand the precise meaning or relation between the following terms: ...
132 views

### Integer factorization based password authentication

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 ...
68 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 ...
75 views

### Could BREACH be used to determine an HTTPS URL?

I was reading this article and had a question.... http://arstechnica.com/security/2013/08/gone-in-30-seconds-new-attack-plucks-secrets-from-https-protected-pages/ As I understand it TLS/SSL work in ...
140 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: ...
106 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) ...
86 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 ...
133 views

### Is this ECC encryption key sharing method okay?

Is this encryption key sharing okay to use? Or is much better to use ECIES? $G$ = base point $a$ = Alice’s private key $b$ = Bob’s private key $A = aG$ = Alice’s public key $B = bG$ = Bob’s public ...
118 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 ...
191 views

### inverse problem about scalar multiplication on elliptic curve

Let $E$ be an elliptic curve over a finite field $F_p$. Given $n$ be a positive integer and $Q$ be a point on $E$, assume that $Q=nP$, how can we find this $P$? We can assume that $n|p-1$. If $n$ is ...
107 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: ...
109 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 ...
101 views

### Question about proof of knowledge defintion?

I am just reading the "soundness"-definition for proofs of knowledge by Bellare / Goldreich. A proof of knowledge is a proof between a prover $P$ and a verifier $V$. $P$ convinces $V$ to know a secret ...
143 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 ...
73 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 ...
59 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 ...
200 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 ...
101 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 ...
76 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 ...
186 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 ...
948 views

### Cryptographic Protocol using NaCl

Why? I wanted to add some security and privacy to a chat-type server for playing various games (with a few things that are done on the server to limit cheating). Going by the "Don't implement ...
317 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 ...
157 views

### Transforming simplest protocol into a Sigma-protocol

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) ...
93 views

### Is this a valid real-time authentication scheme?

The scenario in Alice/Bob/Cindy terms: Alice approaches someone she doesn't know, but thinks is Bob, and asks for some secret information. Bob doesn't know and doesn't trust Alice, but Alice says she ...
120 views

### Computer appliance protocol

I build the computer appliance system that consist of software server and multiple controllers. The system I want to build must be pluggable in the sense that when I connect a controller C to the ...
147 views

### Structure of encrypted office files

I try to find out the structure of encrypted office files (I'd like to implement something like a carving tool for finding certain encrypted file types). I try to understand the Office Document ...
58 views

### Are there any systems like SDSI / SPKI that are currently being developed?

SPKI / SDSI look interesting but appear to have fizzled out and died. Are there any modern competitors?
139 views

### How to properly format a PGP Message Block?

As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ...
144 views

### Security of stream cipher based on Matrix multiplication GF(256) with randomized padding

The actual question is stated at the end of the text. Suppose you have a (grossly inefficient) confidentiality stream cipher with the following components: The keyed function ...
22 views

### Is it possible to design an identity-based key-exchange protocol that has (almost) comparable performance with HMQV and enjoys a tight reduction?

Recently, I'm thinking about a problem that is it possible to design an identity-based key-exchange protocol that has (almost) comparable performance with HMQV, but at the same time, enjoys a tight ...
29 views

### Secure Deduplication and Encryption in a data store

Assume: We have a centralized data store that can store whatever we need Every user is online Users can securely communicate Function $f : File \to Key$ gets access to the store, and is the same for ...
92 views

### practically verifying block ciphers strength

How do we verify practically the strength of a block ciphers? Most of the security analysis of block ciphers is usually around theoretical analysis and proofs in some random oracle model etc. For ...
45 views

### How to distribute symmetric key between $n$ entities?

If there are $n$ servers for broadcasting a symmetric key in such a manner that following holds: No server alone can find the key $K$ alone. Any two servers can pass $k_i$ and $k_j$ such that ...
43 views

### Type G Bilinear Pairings

I was reading PBC and its implementations for finding pairing parameters. I am particularly interested in implementing a BLS signature scheme with 20-byte (160-bit) signatures ("short signatures"). ...
44 views

### Groth-Sahai proofs and hardness assumptions

I am learning Groth-Sahai NIZK proof system for Bilinear groups. While going through the literature, I am getting confused on how the proof system is related to Subspace Decision, SXDH or DLIN ...
65 views

### ECC cryptography with shorter signature when not needing high security?

I am new here and fairly new to cryptography, so if I say something wrong, let me know. I am trying to set up a system where a user can receive a temporary license key over the phone, put it into ...
53 views

### Recover plaintext from truncated ciphertext using AES for FPE

I am trying to implement an FPE for a 19-digit long number. I am trying to follow the lecture of Prof. Dan Boneh and here is how I understand it: Get the nearest power of two greater than \$10^{19} ...
39 views

### IND-CCA2 secure schemes without Plaintext Awareness?

I have been reading up on IND-CCA2 security and was wondering: Are there efficient IND-CCA2 secure schemes that do not require plaintext awareness? I'm guessing yes - could someone point me to these ...
42 views

### Parallel variant of Carter-Wegman MAC with incremental property

Is there a variant of the Carter-Wegman MAC algorithm that is fast, parallel and has the property of incremental crypto?
57 views

### Implementation Attacks on Hashes

So I am familiar with attacking implementations of block ciphers via side channel attacks, cache-timing attacks, etc. What implementation attacks are there against hashes or hashed based functions ...
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### Hardware Implementation of Pairing over BN curves

I am in the middle of FPGA based Hardware architecture design for the computation of Pairing (particularly R-ate Pairing) over BN curves. Where, the point addition, and point doubling should be ...
58 views

### Algebraic Normal Form Piccolo

I'm trying to verify the claim of paper Improved Algebraic Fault Analysis: A Case Study on Piccolo and with Applications to other Lightweight Block Ciphers about the numbers of equations in algebraic ...
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### Universal hashing techniques based on matrix multiplication

The article here says below, about a universal hashing technique based on matrix multiplications. "However, there is a little known method based on using a random matrix. It has lots of advantages - ...