# All Questions

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### What does “G2” mean when used with X509 certficates and certificate authorities?

For example "Google Internet Authority G2"?. I thought it was another way of specifying Class 2 (for organizations, for which proof of identity is required) but then see certificates such as "VeriSign ...
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### Does the initial exchange of random tokens in SKID3 authentication assure against replay attacks?

As the question suggests, I wanted to get a sanity-check on this issue... is it the case that the use of a random token exchange during SKID3 authentication itself constitute a prevention of a replay ...
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### Cracking an appliance's network protocol

I'm trying to crack my thermostat's network protocol. I've captured several rounds of network traffic and here is what I've got to work with. Communicating via HTTP POST The POST data is JSON ...
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### ECIES: Purpose of optional shared information?

According to Wikipedia the ECIES algorithm has two optional shared information $S_1$ and $S_2$. They are used as follows: Generate a random shared secret $Z$ according to ECIES, which will never be ...
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### What does Set Membership actually prove?

While going through this paper, I came across the idea of Set Membership proofs. The proof allows a prover to prove that a value is contained in some set. The point where I am confused is, all the ...
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### 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 ...
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### 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 ...
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### Elliptic Curve based blind signature implementation

I want to use Elliptic Curve based blind signature scheme for my research. There is no proper implementation of ECC-based blind signatures. Can someone describe to me which things I need to follow ...
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### RSA encryption and signature padding flaw

This is Oxford's computer security exam question: Suppose that Bob has published an RSA encryption key $ke$ (retaining in secret the corresponding decryption key $kd$), and Alice has published a ...
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### Proxy re-encryption mod operations

I managed to implement the proxy re-encryption scheme from http://eprint.iacr.org/2009/189.pdf in Python 2.7, however I am having performance issues. As it is, I can run the algorithm for key sizes up ...
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### How can I make a message into a blocks for NTRU?

I have more bits than the degree of the NTRU polynomial. For example: $x^{11}-1$ message: Hello (I am using ascii, 8 bits for 1 symbol) got: ...
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### Common pitfalls of session key activation?

Assume that initiator $I$ and responder $R$ of a key agreement protocol have agreed on new symmetric session keys $K'_{auth}$ and $K'_{enc}$, e.g. by way of Diffie-Hellman and key derivation, possibly ...
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### Special random distribution algorithm

I am implementing ring signatures as a part of an authorization system. Since the number of users could get high enough to make computation on end-user devices infeasible, I am thinking of "...
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### RSA Key Blinding

I was looking the answer to the following question (Timing attack on modular exponentiation), discussing the Private Key Blinding as a countermeasure for timing attacks. Therefore I'm asking if ...
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### Threshold signatures vs. certificate authority+voting verification

Perhaps a silly question, but I am wondering what the advantages are of threshold signatures. Let's consider the following two signature schemes: $(t,n)$-threshold signature with a trusted dealer, ...
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### Index of coincidence for completely random text over k alphabets

I'm confused about /Friedman's method 2 (using a table with column of k size of key, and n/k rows, n is the total size for cipher text) m = \Bigl(\varphi(l)-\varphi(o)\Bigr)/\Bigl(\...
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### Reliability of a single-pass deniable authentication protocol?

I look for one-pass deniable authentication protocol with a short message payload for my project and find a solution: ...
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### Separate TLS Client Write and Server Write Keys in AES-CCM Mode

I am designing a system that uses TLS-like handshaking on a resource-constrained embedded system. I have settled on AES-CCM mode for symmetric session encryption and authentication, allowing ...
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### Delinearization in whitebox techniques

I'm reading through Chow et al.'s paper and Link et al.'s paper. There's a part I don't understand about Delinearization. They convert some steps of AES/DES into a Matrix, then divide the matrix in ...
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### Expand 1-n Oblivious Transfer to retreave only an item I, for which permissions exist

To my understanding in a 1-n Oblivious Transfer the Sender has some Values $X_1...X_N$ and the receiver wants to retreave some $X_I$, with $1 \le I \le N$. Can one now somehow guarantee, that the ...
229 views

### Defending hybrid encryption schemes against padding oracle attacks

I intend to use a generic integrated/hybrid encryption scheme for transmitting information between a client and a server. Key encapsulation: a 128-bit symmetric key is generated and asymmetrically ...
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### Obfuscating point-like functions

There are standard schemes for obfuscating a point function; I'm wondering if we know how to obfuscate a slight generalization of a point function. I'll elaborate more precisely. Definition 1. A ...
108 views

### Timing attacks against RSA, DH and AES

I have been reading about “Timing Attacks on RSA: Revealing Your Secrets through the Fourth Dimension” by Wing H. Wong. I was wondering if this attack is feasible while signing with RSA and, if yes, ...
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### Sane implementations of Bitcoin cryptography routines w.r.t. side-channel attacks

Bitcoin uses SHA-256, Base58Check, ECDSA (Sep256k1) and RIPEMD-160 as the basis of its encryption (see this article for a short guide on how addresses are created). I would like to create an iOS-...
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### Why the same characteristics cannot be used to recover all FEAL4 keys

I am trying to understand how differential Cryptanalysis works. Here I read how to use differential cryptoanalysis for cracking FEAL4 cipher. The big gotcha with this process is that you cannot ...
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### Is ecryptfs safe after unmounting but before turning off the computer

I've read that one of the vulnerabilites of ecryptfs is leaks to swap memory, and that the solution is to encrypt swap. But even if swap is encrypted, it's still open until I reboot. I've also read in ...
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### Weil pairing implementation - low level programming language

I'm just started to studying elliptic curve cryptosystems. My one month-goal is to write a simple signature system based on the Weil-pairing. Some parts of it can be written without deeper ...
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### encrypted file sharing protocol

I am trying to design a file exchange protocol for learning purposes, inspired by PGP, but fixing some of its shortcomings. Assuming the machine where the creation and decryption of the file happens ...
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### Gallant-Lambert-Vanstone method

I am experimenting with the GLV method but cannot manage to get the right results according to the literature. I managed to find lambda, beta, split $K$ into $k_1$ and $k_2$ etc. for the curve I'm ...
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### Known vulnerabilities in (EC-)KCDSA

Does anybody know if there's known vulnerabilities in KCDSA/EC-KCDSA? I have been researching for the past few hours and I haven't found anything. Wikipedia has very limited amount of information and ...
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### For $e(g, d) = c$, can we compute $d$, given others

Given $$e(g, d) = c$$ where, $e$ is bilinear pairing function chosen by the user/attacker, the values of $g$ and $c$ are known $g, d ∈ \mathbb{G}_1$ , $c$ depends upon the $e$ can we somehow ...
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### Why do authors execute a leakage resilient election protocol inside a leak-free phase?

In the paper "Multiparty Computation Secure Against Continual Memory Leakage", on page 1241 (that's page 7 of the PDF) under section 2.3, the authors discuss "The Election Protocol" that they use to ...
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### 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.