# All Questions

89 views

### why $e(g,g)^N=1$ in bilinear pairings holds?

I can't get the point of prime order bilinear pairings:$\mathbb{G}\times\mathbb{G}\rightarrow\mathbb{G}_T$,$g=$ generator of $\mathbb{G}$ , $N=p*q$, $p$ and $q$ primes and $e(g,g)^N=1$. why ...
229 views

### when do we need composite order groups for bilinear maps and when prime order?

Why we need bilinear groups of composite order? What's the special security property of the composite order group in comparison with one of prime order?To put it in another way when do we need ...
494 views

### Calculating the inverse modularity of the determinant for Hill cipher

I'm trying to decrypt a message encrypted with Hill Cipher, but I don't understand how to find the determinant so it solves the equation det * 1/det = 1 mod 26. The determinant for my key matrix is ...
261 views

### Recommended Books for Cryptography : Theory and Implementation [closed]

It is a great idea if experts in Cryptography from mathematicians to security engineers introduce books and textbooks which they think is helpful or instructive for all people interested in the ...
151 views

### Digital Certificate Chain Verification

Does a certificate contain the complete chain of all certificates up to the trusted root certificate, or does the program that verifies certificates have to fetch each parent certificate individually ...
52 views

### Design question for a service that signs messages on behalf of a user

I'm working on a messaging service that lets users author messages and have them signed with an RSA key. The key is used for identity purposes only and can be revoked, so compromising the private key ...
92 views

### Random decomposition of symmetric key

Considering a symmetric cipher (i.e : AES in counter mode), is it possible for any given key to be randomly decomposed into other keys without knowing the message or the ciphertext, such as : ...
142 views

### RSA Signature - Multiple Use Weakness

I cite from Fundamentals of Computer Security (Chapter 7 on Digital Signature, Paragraph 7.3 on RSA Signatures, page 289): Multiple uses of the RSA Signature scheme tend to weaken it. The way out ...
129 views

### Decimal to binary question [closed]

This is an easy question, but I can't explain it lol, how would you guys explain it? There is a procedure for converting a decimal number to binary in the following way: repeatedly divide the number ...
267 views

### Why does my implementation of CBC mode only decrypt the first block correctly? [closed]

I have the following code that uses a CBC mode to encrypt a text by dividing it to 3-elements block. But it only works correctly on the first block which is xored with the IV. ...
148 views

### ECDSA - point order criterion

i am creating some primitive demostration for ECDSA over small curve (p < 229). But my implementation have some weird issues. Verify process return false even if the signature is correct. Because I ...
80 views

### Encrypting documents through a proxy key

Suppose I'm developing an app to secure a lot of documents. These documents were encrypted (say, using AES) with a key X. This key X is basically the password that the user enters before wanting to ...
115 views

### amateur cryptosystem -> a very long boolean expression -> attempt to reduce it [closed]

(newbie here) I try to analyze amateur cryptosystem and wondering, if it's possible to reduce it as reduce a very long boolean expression? What tool can I try to use?
83 views

### Determine complexity of a SAT problem

Is there a standard way to determine a complexity of the specified SAT problem? I'm researching algebraic cryptanalysis and came to solving multivariate quadratic equation systems using CryptoMiniSat. ...
642 views

### What are open problems in cryptography? [closed]

I would be starting groundwork for my thesis in cryptography , I would like to know what are current open problems in cryptography, few I know of are Fully Homomorphic Encryption Functional ...
21 views

### Pohlig-Hellman exponentiation block cipher

Let $G$ be a group of order $n$ and let $e,d$ be integers such that $ed\equiv 1 \pmod{n}$. Then the exponentiation maps $x \mapsto x^e$ and $y \mapsto y^d$ are inverse maps on $G$. These maps give us ...
45 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? ...
46 views

### Using public key infrastructure or hashing for personal identification privacy? [on hold]

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 ...
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
28 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 ...
14 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 ...
35 views

### A replay attack question

Which of the following protocols is susceptible to replay attack :- 1) A -----> B username, password 2) A -----> B username, h(timestamp,password) 3) A -----> B username timestamp, ...
24 views

### Correlated or biased coin protocols?

There are a number of papers in the literature describing secure/fair coin flipping protocols. Unfortunately in my case, I am looking for coins that are epsilon-biased or epsilon-correlated. I am ...
60 views

### If H(m) = 0 for some m, how can a DSA signature be forged?

If we know for some message $m$ that $H(m) = 0$, how can we forge a DSA signature with only the public key? I got that $g^s*r = (g^x)^r$ where $x$ is the private key, but that's one equation with 2 ...
26 views

### Why doesn't this authentication protocol work? [duplicate]

I am a student taking a cryptography course so forgive me if this comes off as a silly question. This is an assignment question: Alice ------R--------> Bob Alice <-----[R]B------ Bob Alice ...
47 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 ...
62 views

### How does Google's “authenticator number generator” work?

I have two-factor authentication enabled on my Google account, and I have this app on my phone which generates a number I have to type when I'm logging in to Google-Mail. But I don't understand how ...
101 views

### Blum-Blum-Shub Cryptosystem

I am given $N$, which is Bob's encryption key. I was able to successfully factor $N$ into $N=p*q$. Alice encrypts a messages for bob and sends $a = [1,1,1,0,0,0,1,0,1,1,0,...]$ $b = 1545164156...$ ...
65 views

### Differences between working of Tor and onion routing [migrated]

I am learning about Tor and Onion routing and I'm trying to compare both services. From the wiki link, I can see that Diffie Hellman (DH) handshake is used and when look into the “tor-design.pdf” for ...
42 views

### On the structure of the UOV (Unbalanced Oil and Vinegar) signature scheme [closed]

I'm study Multivariate Quadratic Cryptography. I like to know why, in opposite to other multivariate schemes, the second afﬁne map S is not needed for the security of the UOV signature scheme? ...
20 views

### User's Privacy in certificateless cryptography

In practically, while doing registration with Key generation center in certificateless Signature,How can be a user do registration to the Key generation center without providing (Global ...
26 views

### Why have AH and ESP security protocol when we could just encrypt packet with a symmetrical key?

Why have AH and ESP security protocol when we could just encrypt / decrypt packets with a symmetrical key and with some block cipher using that symmetrical key?
33 views

### Can you clarify the proof that secure LR-two party protocols do not exist?

In the paper “Multiparty Computation Secure Against Continual Memory Leakage” on pg. 1237, the footnote #1 discuss why it is not possible to construct a leakage resilient two-party protocol. But I'm ...
17 views

### TCR hash functions from MD5

I'm reading Collision-Resistant Hashing: Towards Making UOWHFs Practical (pag. 10 and 11) and here say The most direct way to construct a TCR hash function is to key a function like MD5 or SHA-1. ...
63 views

### PNG converted to BMP — and encrypted with ECB [closed]

This is not a cryptography question, but after searching for the answer to no avail, I resort to asking it here. In a vein similar to what is done here, I've encrypted a BMP image in ECB mode. And ...
79 views

### becoming a cryptographer after math studies [duplicate]

after studying philosophy and being a philosophy teacher, I took back studies 4 years ago and I did a bachelor in maths. I'm in maths grad school now (I'm 32), and I would like to work in ...
22 views

### Masking Parity Check Matrix Goppa

I like know: Is possible that any adversary PPT will be able to find the generator matrix $G$ of Goppa code $GC$, if given $SH$ matrix, where $H$ is a parity check matrix of $GC$ and $S$ is a random ...
45 views

### Reusing PGP key when generating SSL Certificate Authority?

Does it make sense to reuse some of the keys from my PGP (gnupg, gpg) keyblock when generating my own SSL Certificate Authority (a toy one for myself and a few web services of mine)? In an ideal ...
24 views

### How to retrive secret key from java keystore in .net [migrated]

I use java symmetric key encryption for encryption and decryption, key used for this is stored in java keystore and now I have to decrypt the content on .net and to decrypt the content I requires the ...
10 views

### Why does a joint leakage MPC protocol not directly apply to a disjoint leakage requirement?

In this paper on pg. 1239 the footnote at the bottom points out the difference between $joint$ leakage and $disjoint$ leakage. The authors say the weakly leakage resilient protocol of BGG+11 cannot ...
49 views

### How do you prevent the risk of damage to the security of Fully Homomorphic Encryption?

In this paper on pg. 1248 in the "preprocessing phase" section the authors say: In the preprocessing phase, the parties run a (standard) MPC to collectively generate a key pair (pk,sk) for the ...
57 views

### Why does WPA2-PSK use 4-way handshake instead of 2-way handshake

I don't seem to grasp why is the handshake for PTK in WPA2-PSK 4-way and not 2-way. Isn't it enough to just have these two steps: First party sends Nonce1 to the other party Second party sends to ...
66 views

### VPN Authentication over WiFi — Is it secure? [migrated]

Count this question as part of my ignorance on how authentication scheme is done on your typical VPN session. But here goes: We often advise the security-conscious user that if one must use an ...
59 views

### Unblind a RSA blinded signature

I have blinded m = 16 with r= 13, e = 7 and n = 209. This resulted in m' = 464, which led to a s' = 8. Now, I want to unblind this s' by using s = s' * r$^{-1}$ but im stuck at filling in the ...
66 views

### How widely is Perfect Forward Secrecy in HTTPS clients? [migrated]

We are hosting an SaaS website and API with the https protocol, both of which are accessed by numerous users with a lot of different browsers and client-side apps. What would happen if I made PFS ...
39 views

### AES and Known-plaintext attack [duplicate]

Can you help me to finding some papers that shows AES is secure against known-plaintext attack?
65 views

### Why use a timestamp and how can someone know it's the correct one?

Let's say A wants to send a message, so everyone who gets the message, can be assured that it's from A. A then sends a message : ...
I know a protocol for bit commitment using regular OT (Bob has 1/2 chance of learning the bit Alice transferred to him) which goes like this: COMMITMENT PHASE Alice chooses a bit $b$ For ...