# All Questions

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### Hard drive security

I had a idea of making a secure hard drive https://en.wikipedia.org/wiki/Data_security. And add some new ways, so I wanted to ask does any body have a idea how to make a hard drive infect a forensic ...
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### How can an email sender include his PGP key, so I can answer with an encrypted mail? [migrated]

Let's say I were to post my e-mail address and public PGP key to my website. When a client contacts me, they would have to include their PGP public key in the e-mail so that I can respond to them in ...
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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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### How is the following different than RSA Signing of a document?

If the goal is to demonstrate that you are who you say you are, I think the following will work: Bob wants to know that you are Amy. Bob encrypts a number using Amy's public key and then asks her what ...
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### Is MAC algorithm same at both sender and receiver end

The MAC algortihm which is used along with a secret key to generate a MAC tag on the sender end ,is it same at the receiver end also who again uses a MAC algorithm to generate a tag? If yes, then how ...
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### How to make a document truly read only

How is it possibile to cryptographically make a document truly read only? As in read only I imply that the user can obviously view it which can be achieved by coding which pixels have which colors. ...
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### Are symmetric and asymmetric keys both used in SSL/TLS

As far as what I have understood, both symmetric and asymmetric keys are used in SSL/TLS, is it right? The SSL/TLS uses Asymmetric Keys (Public key encryption) to generate a session key. The session ...
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### Why is the P-521 elliptic curve not in Suite B if AES-256 is?

In the NSA's document, "The Case for Elliptic Curve Cryptography", we have ...
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### Can Pre-Paid Cards be cracked?

Is it possible to deduce the original function that used to generate those prepaid cards number that are used for charging your mobile phone credits? For example: If I've collected about 1000 of ...
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### Repeatable crypto

Is there a safe way to do crypto that will always produce the same result for a given input? My use case is transferring deltas of huge files, to a backup server. The backup server has no knowledge ...
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### FSB Hash Functions and Convetional hash Functions

I'm reading FSB cryptographic hash function and the authors say that security of this function depends on NP-Complete Problem: "Decoding Linear Code Unlike most other cryptographic hash functions in ...
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### Privacy-Preserving relational databases: checking the existence of a record (or multiple records)

I would like to know if there exists a protocol which performs the following operation in a privacy-preserving fashion: User $U$ wants to know whether a record is stored in the database. The primary ...
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### OCB and GCM security

Is OCB as secure as GCM or CCM ? Since OCB design is quite different from GCM and CCM, I was wondering if the security properties of these latters are satisfied by OCB, as well. Thank you.
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### SIMONs Cryptoanalysis

I'm reading Cryptanalysis of the SIMON Family of Block Ciphers. In Section 3.1, it says: For SIMON, consider an n-bit input difference $\alpha= x\oplus x'$ to $F$ of Hamming weight one. As the ...
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### Is SHA related to AES or TLS in any way

I have been reading about SHA-2 family and I found a lot of in depth details, but I am confused about how it is related to TLS and AES. TLS encrypts data between server and client, but does it make ...
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### Is multiple encryption using NaCL and TLS better?

In general, the idea of multiple encryption sounds interesting - for creating stronger cyphers (especially against implementation bugs), one could always get the configuration details wrong and mess ...
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### Prevent MITM attack while encrypting data by using ElGamal ECC?

I am using ElGamal ECC to encrypt my plain text data. I want to ensure that my data is safe from a Man-In-The-Middle attack. What methodology I can adopt to achieve this goal? How can we prevent a ...
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### CBC-MAC based on PRF

Why is the block cipher in the CBC-MAC taken to be a pseudo random permutation (PRP) and not a pseudo random function (PRF)? We don't need the bijective property of the PRP. So why go with it?
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### Should layered use of crypto always have a cryptographic binding between the layers?

Reading the latest TLS weakness, it seems that multiple weaknesses have been found over the years caused by not ensuring that messages are sent over the same channel, and in general a lack of ...
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### why should one use lattice-based systems in travel documents in post- quantum computers era? [closed]

What are the attack algos and complexities to break lattice based systems What is the motivation for using lattice crypto? How does shor's algorithm work exactly? why it has not been used extensively? ...
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### Desirable S-box properties

What desirable properties should an S-box have? My current standard selection process is to just pick them at random and verify that they fit the following criteria: The probability that any random ...
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### Asymmetric algorithm for one time signing of small cleartext

I want to generate a key pair such that the private key can be used once to sign a small message (1024 bytes) at some indeterminate point in the future and the public key can be used to verify that ...
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### 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 Function $f : File \to Key$ gets access to the store, and is the same for all users. $g : Key \to File$ ...
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### garbled circuit vs fully homomorphic encryption

Consider an outsourced database to an untrusted cloud (think CryptDb), the question is how to compute a function $f(.)$ on the data. I think I understand how (fully or partially) homomorphic ...
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### Are partial hashes used in cryptographic protocols?

In my question (and answer) about a partial hash code used within a signature application I found out that partial hash codes are sometimes used within protocols with a relatively restricted security ...
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### Could RDRAND (Intel) compromise entropy?

I was recently discussing the issue of RDRAND in Intel chips and the whole issue about how NSA could potentially be influencing Intel to weaken or create backdoors in their design. This petition was ...
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### Hash collision resistance requirements for Lamport signatures

According to the original paper, Lamport one-time signature scheme uses two one-way functions: $F$ and $G$. The former one, $F$, is used to create a public key by hashing elements of the private key ...
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### Homomorphic Encryption: how does the equality test on ciphertexts work?

Let's suppose we have a asymmetric crypto-system $H$ which is homomorphic with respect to some function $F$. Alice encrypts a message $m$ with her private key $e$ in the crypto-system $H$ and ...
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### Do any non-US ciphers exist?

Plenty of ciphers come out of the USA from government research or selection competitions. AES and DES are examples. Are there any public ciphers produced by other states, China or Iran for example? ...
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### PGP String to Key specifiers

I've been reading through the PGP Standard and here I'm a little confused. This section is discussing converting string data to a session key. I'm confused about the paragraph in bold. First off, what ...
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### What are Cryptographic Multi-linear Maps?

I've encountered this term many times in the fields of Fully-Homomorphic Encryption and Obfuscation. I want to learn those subject and Cryptographic Linear Maps seems to be an obstacle in the way. ...
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### Managing data permissions/access through asymmetric cryptography

I want to manage authorization, as 3rd-party permissions, through asymmetric cryptography. I'm concerned about how is it possible to share access of encrypted data with N entities, and be able to ...
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### 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 ...
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