# All Questions

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### How is a PRNG used in the PGP?

I'm currently reading up on the components of PGP and I am wondering what exactly the PRNG is used for. PGP uses ANSI X9.17 and entropy from a users keystrokes to generate a temporary key. So, is ...
38 views

### Diffie-Hellman: Does the size of the prime modulus depend on the potential size of the secret?

I'm writing my own cryptosystem that uses One Time Pad and Diffie-Hellman to generate keys for the OTP. I am using Rails on the server side and Javascript for the client side. Please don't tell me ...
36 views

### Could someone reuse client certificates?

To my understanding, if a server “cert+key” (RSA) is compromised, than the SSL/TLS network traffic can be decrypted. What about a client “cert+key” (RSA)? Could someone reuse client certificates? ...
23 views

### Concepts of Pairing based crypto [on hold]

I want to learn concepts of pairing based cryptography in detail. Please suggest some books or sites to learn all the concepts from basics.
10k views

### Should we MAC-then-encrypt or encrypt-then-MAC?

Most of the time, when some data must be encrypted, it must also be protected with a MAC, because encryption protects only against passive attackers. There are some nifty encryption modes which ...
1k views

### What exactly is a negligible (and non-negligible) function?

The mathematical definition of neglible and non-neglible functions is fairly clear-cut, but why they are important and how they are used in cryptography?
22 views

### Is it possible to modify SSL handshakes to enable PFS while still using RSA during the handshake?

I know we could possibly be using DH key exchange, that would enable PFS. However, what if we make modifications on our SSL 3.0 handshake such that the only cipher we use is RSA for the achieving PFS? ...
61 views

### How well does breaking multiple DH key exchanges over the same group scale?

Suppose you are running a server with the Diffie-Hellman parameters (so the group G and generator g) generated once. There are ...
369 views

### What does Maj and Ch mean in SHA-256 algorithm?

I'm guessing they're some kind of standard function but what do they do and what do the names mean? A little explaination or link me to an article would be great.
55 views

### How should I manage Diffie-Hellman parameters on a Web Server?

Is there a best practice for Diffie-Hellman parameters (p, g, and q) used on a web server? The server is using ephemeral keys, but should the parameters be rotated on a regular basis? Is it OK for ...
29 views

### Can you provide an example in relation to Hidden Field Equations Multivariate?

I'm reading about Hidden Field Equations Multivariate scheme. My lecture states that the central map is a univariate polynomial $$P(X)=\sum_{i=0}^{r-1}\sum_{j=0}^{r-1}p_{ij}x^{q^i+q^j} \in K[X]$$ ...
35 views

### Using public key infrastructure or hashing for personal identification privacy?

I've been reading about identity theft recently, and I'm wondering about some possible solutions using the techniques of asymmetric/symmetric/hashing in encryption. My idea is going to cross those 3 ...
17 views

### Where can I find examples of ECC implemented in VHDL?

I am looking into implementing ECDSA signature and ECDH key agreement in a Xilinx FPGA. All the examples I have found of VHDL implementations skip over how to construct the low level ECC primitives ...
48 views

### Would this prevent FNV1a 32 bit hash collision?

I am considering the FNV1a 32 bit hash as part of a simple software security and authentication system. I am aware that FNV1a is NOT ideal but it may suit my needs. I am aware that FNV1a has rather ...
181 views

### Slow one-way pseudorandom permutation?

I'm looking for a slow one-way pseudorandom permutation; or in other words a block cipher $E_K: P\in\{0,1\}^b\mapsto C\in\{0,1\}^b$ with moderate block size $b\approx 64$ bits, wide key $K$, ...
225 views

### Why are cryptography algorithms not exported to certain countries?

There have been strict laws about the export of crypto software to certain countries. I can understand the intent, but never gauged the fact that there is nothing stopping these countries from ...
31 views

### Can a zero knowledge proof (or MAC) be generated from human-typable input?

Edit: My goal is to create a voting scheme that doesn't require a lot of crypto infrastructure to be deployed on the client side. Smartcards, and tokens are impractical for these purposes. I ...
189 views

### How hard is to invert the function that computes the middle-bits of (x^2)?

I'm designing a function f that should be moderately hard to invert and very fast to evaluate in a modern CPU. The function will be used in a proof-of-work function. I've read that the middle-bits of ...
68 views

### Does SpongeWrap (from the Keccak team) absorb ciphertext or plaintext?

I have been reading the Cryptographic sponge functions paper, but I'm still confused. Does Keccak in authenticated encryption mode absorb ciphertext or plaintext? Edit: Are there any test vectors to ...
464 views

### Alphabetic Substitution with Symbols

I was reading on a site about the Zodiac Killer and how he used a basic substitution cipher, but instead of substituting english letters and characters he substituted symbols. I was wondering, if you ...
89 views

### How does this happen in RSA malleability?

I don't understand how the $E(m)$ turns into $E(mt)$. I mean, I don't know how does that transformation happen and how does the equation occur. $$E(m) \cdot t^e \bmod n = (mt)^e \bmod n = E(mt)$$ ...
55 views

### Assuming that we had a way of finding primes, could RSA be used without computers?

I once asked a question "Would RSA make sense if we used no computers?". The answer was negative, because finding primes that would make secure keys would prove too hard. Assuming that we had found ...
53 views

### PRP representation size

I'm now studying the block cipher substitution-permutation network construction and realized that it uses several small pseudo-random permutations instead a big one for saving memory (or that is one ...
264 views

### security of Felix cipher

I just find this pencil and paper cipher 'Felix' and I want to know how secure it is? EDIT From http://web.archive.org/web/20110825142054/http://topcat.hypermart.net/papers/felix.txt Felix a ...
195 views

### Can you help with that definition for a CCA?

The following is a definition taken from Introduction to Modern Cryptography by Katz and Lindell. I'm having a hard time understanding some basic concepts! Can you please help me? ...
106 views

### Why is it that researchers prefer finding secure software solutions over secure hardware solutions?

My understanding is crypto researchers tend to prefer solving a problem in software without the need for secure hardware. Why is this? What is the big problem with using secure hardware if the ...
46 views

### What is “serial concatenation”? [on hold]

I have a third-party point-of-sale API (Speedflow Pay-N-Get) that I am trying to communicate with over HTTP, but I have a problem with it. In a nutshell, a request is encrypted using RSA, and the ...
65 views

### Can you explain “weak keys” for DES?

A weak key for DES is a key $K$ such that $DES_{k_1}(DES_{k_2}(x))=x$ for all $x$. I don't get why are the 4 keys $k_1||k_2$: $1^{112}$, $0^{112}$, $0^{56}||1^{56}$, $1^{56}||0^{56}$ considered as ...
64 views

### Can you help me with this DES variant analysis?

I'm struggling with some DES variant that I got as an exercise (exercise taken from Katz-Lindell Ex5.14). The variant is as follows: The left half of the master key is used to derive all the ...
51 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 $x \in Z^{*}_{N}$ ...
46 views

### Find the key to a Vigenère cipher, given known ciphertext and plaintext

I have the ciphertext and the plaintext. Is it possible to know the key? If not, what do I need to find it?
68 views
+50

### Is there a Pairing-free ID-based AKE protocol that is secure under the eCK model?

As far as I know, most of ID-based authenticated key exchange (AKE) protocols are CK-secure, and there are few of them which are eCK-secure. All of the eCK-secure ID-based AKE protocols use the ...
28 views

### Is it feasible to implement my encoding module in multi-threaded mode? [on hold]

I am working on data integrity protection scheme, as described at “FMSR-DIP: Enabling Data Integrity Protection in Regenerating-Coding-Based Cloud Storage ”, in which my DIP encoding module works on a ...
66 views

### What is a good analogy (which a layperson would understand) for the process of Bitcoin mining?

I will be explaining Bitcoin to a non-technical group and I am hoping somebody can provide me with a very basic visual analogy of the crypto-currency mining process. My half-baked idea, was to ...
61 views

### Asymmetric Cryptography Confusion - 'Sign' a file to guarantee its source

What I want to do is use asymmetric crypto to guarantee that a file comes from a source. I have software that runs on lots of wireless devices, and each of those has a license file with an encrypted ...
133 views

### Why should I use Authenticated Encryption instead of just encryption?

There are various different modes of operation for block cipher use, some of which provide "encryption" and some of which provide authenticated encryption. Why should I use an authenticated ...
56 views

### What is a Message Transmission Scheme?

I've been given as an exercise to show an encryption scheme that is CCA-secure but is not a secure message transmission scheme. What is a message transmission scheme, and how does it differ from a ...
108 views

### How do I calculate the private key in RSA?

Given $n=pq$ for $p,q$ known, I can calculate $\phi(n)$. $e$ is selected such that $\gcd (e,\phi(n)) = 1$. Using this, how do I calculate the RSA private key? Example: I have $n = 35$, with ...
45 views

### why RSA uses Semiprime numbers? [duplicate]

Why does RSA use semiprime numbers? Why not just use any big number ?? What is the advantage of the two original numbers being prime? Because factoring any big number will be difficult
121 views

### Why are these techniques not feasible to crack RSA?

For $d = e^{-1} \mod \phi(n)$ $$d\cdot e \operatorname{mod} \phi(n)=1$$ $$d = (e^{-1} \operatorname{mod} \phi(n))$$ With having $e$ and $n$, we can calculate the value of $d$ , the private key for ...
45 views

### unknown Transposition ciphertext [closed]

What cryptanalysis can be made to find the transposition code for a cipher: it's not railfence, slidefair, classical rectangular by rows or columns, or double rectangular, or Ubchi. For a ...
50 views

### Regex searchable word list for space-less monoalphabetic substitution

I am working on teaching myself basic cryptography, in the process I created a simple substitution cipher based on a single alphabet, and a statically defined offset (no key for now). Now that ...
85 views

### Perfect secrecy over Stirling numbers

For all $c_0\leftarrow m_0 \oplus k$ there exists a $k'$ such that $c_1 \leftarrow m_1 \oplus k'$, where $m_0 \neq m_1$ and $c_0 = c_1$. Assuming a truly random $k$, the first assignment is a ...
137 views

### Keyed digest function with odds of collision below the birthday bound?

I wonder if it is possible to devise a function $F(K,S,R_S)\mapsto D$ where: $K$ is some key (I have freedom on $K$, it could even be generated by a trusted party); $S$ is in $\{0,1\}^s$, say ...
360 views

### Attacks on the RSA Cryptosystem

I was reading some articles about attacks on RSA system and I wonder about some generalization of the following theorem. Theorem (Coppersmith). Let $N=pq$ be an $n$-bit RSA modulus, where ...
64 views

### How can I tell how many bits of security a secure hash function has?

How can I tell how many bits of security a secure hash function has? For example, how would I calculate or tell how many bits of security a secure hash function with 160 bits output would have? ...
27 views

### Will ecryptfs prompt for mount passphrase if configured to mount at fstab [on hold]

I am aware that encryption at boot is often accomplished with luks dm-crypt, however it would appear that dm-crypt can only handle fixed length containers or partitions. It would be convenient to ...
13 views

### Is it possible to change an ecryptfs mount/file passphrase? [on hold]

Is it possible change the mount passphrase of a ecryptfs mount? (not the wrapping passphrase of a ~/Private) I have a recollection of reading something about ...
15 views

### Where is the declaration of execution of ecryptfs for on user login automount? [on hold]

For a ~/Private mount generated by the ecryptfs helper utility, where is the declaration to (check for the automount file) execute ecryptfs on user login? Same ...
147 views

### Can insecure algorithms be combined to form a secure algorithm?

This is hypothetical as I can't think of any reason to do this, but out of curiosity.. Could I, for example, take the MD5 digest of a message and concatenate it with the SHA-1 digest (not quite ...

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