# All Questions

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### Isn't Groth-Sahai proof system applicable beyond Bilinear groups?

Classical paper by Groth-Sahai on NIZK proof system is titled as "Efficient Non-interactive Proof Systems for Bilinear Groups". To my understanding, only (Pairing Product Equation) PPE are defined ...
24 views

### secure embedded/microcontroller crypto using AES-ctr with hmac-sha2

The embedded device is a low-power 8-bit microcontroller (memory usage is constrained to about 10kb code, 1kb ram). As the device is battery-powered and manual service should be minimal, more powerful ...
37 views

### How to establish if a string contains a message

If you have a string S, then the string can be composed of four things: cleartext 'random' data encrypted data compressed or otherwise non-encrypted, but modified, cleartext If you want to see if ...
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### Verifying DER encoded DSA/ECDSA signature with extra content?

If you have a DSA/ECDSA signature, which is supposed to be DER encoded as an ASN.1 sequence of r and s (as in the RFC), if you're given some bytes which are ...
27 views

### How to remove blind factor from a blinded message in RSA?

I blinded the message using below formula. Blinded message=Message⋅r^e Now i want to give this r (the blinding factor) and need to unblind the message.
12 views

### PGP Encryption for Files on a Mac

Is there a way I can encrypt files on my Mac using my pgp key with an easy to use gui?
55 views

### Can a secret message be securely transmitted within a MAC tag?

A sender wants to transmit an ultra secret code $M$ which could be either 'go', 'stop' or 'wait'. This could be any selection of code words really and adopted for any use such as transmitting short ...
25 views

### Undrestanding hashing algorithm with MD5 in Javascript

For some time I've been searching for string encryption method inside Javascript. after some search I've found this solution as indicated below, however I can't understand it fully and get stacked ...
49 views

### Meaning of Multiplicative Group to the power n i.e. Z^n

What does $Z_q^n$ mean in this notation?      References: on the 2nd paragraph of page: http://en.wikipedia.org/wiki/Learning_with_errors
43 views

### Secure(delegated, outsourced) computation

Can we think "secure (delegated and outsourced) computation" as a same single concept, or should we consider these secure protocols as different concepts? If these are different, how to distinguish ...
26 views

### Mistakes in Jarecki-Liu use of Camenish-Shoup encryption?

I am implementing a protocol that uses Jarecki-Liu OPRF, which itself uses a simplification of Camenish-Shoup Encryption. Description of the way they do Camenish-Shoup is in section 2.3 of ...
67 views

### Cracking RSA with Small exponent 5 [on hold]

I have read following questions - Cracking an RSA with no padding and very small e Small Encryption Exponent where in first it says to run out all the possible m options and second says factor ...
62 views

### Minimum number of independent trials needed to detect a bias

Suppose, I suspect that the probability of occurrence of a particular bit as $0$ is $.558$. Since, it is not $.5$, so this is possibly a bias. Now, my question is: What is the minimum number of ...
78 views

### Where to store the file extension to retrieve it correctly after decryption

I am using Java to write AES-256 to encrypt various files with different extension, the problem is, where am I suppose to store the file extension so the if the data is decrypted, the file extension ...
113 views

### Maximum length in bits of the product n=pq

If p and q are two 1024-bit prime numbers, would the maximum length in bits of product $n=pq$ be ${1024}^2$ or $2^{1024}$? I think it is ${1048576}={1024}^2$? Also, would the least significant bit ...
25 views

### Finding Elliptical curve points and encoding text using them

I recently got into learning Elliptical curve cryptography and are currently building a project in C#. Everything is working well so far, I can encode and decode points, and thanks to this forum I ...
59 views

### Repeatedly using same key on different plaintexts

Symmetric encryption: Does using the same key over and over again introduce a vulnerability? Meaning, if I transmit a different piece of plaintext encrypted with the same key every day, will an ...
37 views

### Does MD5 hash have quasi commutative property?

I am implementing a one-way accumulator using MD5 hash, wondering wheather it has quasi commutative property or not.
31 views

### best scheme hash function for block cipher? [on hold]

between Miyaguchi-Preneel, Davies-Meyer and Matyas-Meyer-Oseas, which is the best hash function scheme for block chiper ?
32 views

### Using Diffie-Hellman key to establish a shared key $K_{AB}$

I have a question on Diffie-Hellman key and want to check that my solutions are correct. Alice and Bob intend to use Diffie-Hellman key agreement to establish a shared secret key value $K_{AB}$. ...
30 views

### A proof exercise in the <<Intrduction To Modern Cryptography>>

I'm learning the book by myself. I have thought this exercise for few days.But I still don't get the way to proof it. Any help would be appreciated. Thanks.
48 views

### How Brittle Are LCG-Cracking Techniques?

One thing that perplexes me somewhat about the cryptographic community is how people seem to hate LCGs and write them off without much effort to repair their flaws, and yet also like LFSRs and have ...
135 views

### Generalize the Merkle–Damgård construction for any compression function

I am trying to figure out this question: Generalize the Merkle–Damgård construction for any compression func­tion that compresses by at least one bit . You should refer to a general input ...
221 views

### Finding a collision for a hash function

I'm trying to find a collision for the following (modified) Merkle–Damgård hash function. Suppose we already have a hash function $h : \mathbb{Z}_2^{2·n} \to \mathbb{Z}_2^n$ for fixed length bit ...
49 views

### Merkle–Damgård transform: necessity of the Length block [duplicate]

The Merkle–Damgård transform append the message length (in blocks) to the message itself and then computing the 'chained hash' algorithm. Does the last block (which contains the length of the ...
172 views

### Why is an IV used in Merkle–Damgård transform?

In Merkle–Damgård transform, a fixed vector IV is chosen at the beginning, and it is hashed together with the first block x1. I wonder why we don't use x1 straightforward, i.e. hash x1 and the next ...
106 views

### Different padding rules for Merkle–Damgård and Keccak/sponge function

We learned that length padding was used in Merkle–Damgård where after padding with zeros another block is added that contains the initial length of the input. This is supposed to prevent same hash ...
37 views

### Collision in Merkle–Damgård without a collision in compression function

Is it possible to find a collision in Merkle–Damgård just by omitting the extra one bit that is appended to each input without having a collision in compression function?
38 views

### Is the Vigenère Cryptosystem malleable?

Is the Vigenère Cryptosystem malleable, and how can we prove that it is (or it is not) malleable?
161 views

### Are there any digital signature algorithms in common use that result in 32-byte signatures?

I don't consider myself to be an expert in this field, so forgive me if there is an obvious answer. I am having a tough time finding an algorithm that can sign data and output a 32-byte signature, ...
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### How is security of server's RSA private key is ensured? [migrated]

We repeatedly hear news of hacking of passwords from PW database (server side) but nothing about hacking of server's RSA private key (not asking regarding finding p and q for a given public modulus ...
36 views

### RSA OAEP: prevention of partial decryption of ciphertexts

I'm trying to understand RSA encryption (as a beginner in cryptography). go on this wiki page http://en.wikipedia.org/wiki/Optimal_asymmetric_encryption_padding scroll down to the 2 numbered points: ...
38 views

### simulating rc4-256 with rc4-128

OpenSSL supports rc4 with 128-bit keys and rc4 with 40-bit keys. It does not support rc4 with 256-bit keys. My question is... is it possible to modify the state of the pseudo-random generation ...
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### can you suggest any applicayion for implementing threshold homomorphic encryption cryptosystem(Paillier cryptosystem) [on hold]

I want to implement one project in multi party homomorphic encryption using paillier. Can you suggest any application for implementation.
149 views

### Secure degree reduction for Shamir's secret sharing

I understand the basic Shamir Secret Sharing protocol, and when two shares are multiplied, the degree of the polynomial increases. I've seen in a number of papers a reference to a degree reduction ...
46k views

### How secure is AES-256?

The cipher AES-256 is used among other places in TSL/SSL across the Internet. It's considered among the top ciphers. In theory it's not crackable since the combinations of keys are massive. Although ...
30 views

### Email Encryption [migrated]

I'm hoping someone can point me in the right direction. If I wanted to implement email encryption within an organisation what would be the best way? I've been searching the web tonight but all my ...
59 views

### Computation indistinguishability questions

The definition I have is: Two probability ensembles $X = \{X_n\}_{n \in \mathbf{N}}$ and $X = \{Y_n\}_{n \in \mathbf{N}}$ are computationally indistinguishable if for every probabilistic ...
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### Diceware word list for six dice

I really like Diceware, but it now needs six words to be safe. Instead of adding a word, I would think that increasing the size of the wordlist and adding an extra dice would be a better idea. I have ...
59 views

### Can someone please explain to me what this means? [on hold]

I'm taking a cryptography class and I was assigned this for a project: Implement automatic ElGamal text encryption/decryption I'm not sure what it means (but I'm familiar with discrete logs and ...
29 views

### CoAP authentication using DTLS

what is the meaning of this notation ?? AES{Yi, (Yi XOR Ki | nonce1)} https://tools.ietf.org/html/draft-bhattacharyya-core-coap-lite-auth-00
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### Elliptical curve cryptography key generation time

I am currently trying to learn more about Elliptical curve crypthography and have finally started to get things working and undestanding the different pieces. I've written a small project in C# and ...
23 views

### Javascript Information Dispersal Algorithm [on hold]

I am trying to implement a webapp that is encrypting and distributing files on multiple clouds - similar to the DepSky system (http://www.gsd.inesc-id.pt/~mpc/pubs/eurosys219-bessani.pdf), but I am ...
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### Sharing an encrypted file between a group of people

Is there any way to share an encrypted file with a group? In the other words, can I encrypt a file with a public key so that each person in a group decrypt it with his/her private key? Is there any ...
58 views

### Bilinear Map vs Inner Product [migrated]

What is the difference between a Bilinear Map and a Inner Product?
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### Maturity of searchable encryption schemes [on hold]

Is searchable encryption industry ready with product implementations?If yes kindly give me the name of products over which it is used.
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### Gap problem for Learning With Errors

Informally, a "Gap" problem is the one that arises when solving the computational (or search) version using an oracle for the decisional version. For example, the Gap Diffie-Hellman Problem (GDH) is ...
155 views

### When would one prefer a proof of knowledge instead of a zero-knowledge proof?

I've just realized I find it hard to distinguish between these two terms (proof of knowledge, and zero-knowledge proof), specially where only the latter seems to be used in many cryptographic ...