# All Questions

1answer
88 views

### SHA-256 “almost unique”?

I have seen numerous references on the internet of people describing SHA-256 as generating an "almost unique" hash. Exhibit A. there are more. Is there some mathematical basis to the almost ...
1answer
212 views

### Proper way to generate symmetric keys

I'm trying to educate my self in key management, how to store them, how to generate them, how to use them properly. I've been trying to find how you would generate a key for symmetric encryption (say ...
0answers
17 views

### What is the proper way to delete a file which had secrets in it? [closed]

Keep in mind that nowadays, on most UNIX systems, filesystems are journalized. So the shred command does not work, for example.
1answer
131 views

### Attacking hashed password by timing attack and other means

This question is inspired by this recent one, which raises a point that need to be made quantitative to be meaningfully discussed. I chose an unusual approach: a new question worded as homework that ...
0answers
49 views

### How to break a columnar transposition cipher?

I'm currently studying for a cryptography exam. I've been given ciphertext that has been encrypted by a columnar transposition cipher. I've been given no shift key length or key word, the only thing I ...
2answers
47 views

### Probabalistic Polynomial-time Algorithms & One-way functions

I've been reading up on probabilistic polynomial-time algorithms and one-way functions, and I was hoping to get some guidance on the topic. A textbook I'm reading states the following for one of the ...
2answers
561 views

### Generating unbiased numbers with a biased six sided die?

Eve takes a fair six-sided die and adds some heavy paint to the side of the die with the 6 on it. This results in a biased die that rolls a 6 with probability 2/7, and each other number (1-5) with ...
1answer
38 views

### What does CA certs contains? public key of site or CA?

I believe it contains public key but whose? the site like a bank or the certificate authority who has signed?
1answer
74 views

### What is the impact of a server not fully verifying the data in the Client Finished packet of a TLS connection?

F5 BIG-IP devices suffer from a vulnerability in which not all bytes of the Finished packet in a TLS connection are validated. The sort-of technical description can be found here. F5 don't consider it ...
0answers
22 views

### Prove that complement of plaintext and the key, then ciphertext will be the complement of orig. ciphertext [duplicate]

I'm trying to prove in general terms the following: y = DESk(x) then.. y' = DESk'(x') I can plug in random variables for ...
0answers
62 views

### Weird base64-like (?) encoding [closed]

I have some encoded strings which are probably encoded in a base64-variant - except that there aren't only 64 chars, but all the (printable) ASCII chars between 33 and 126 (0x21 to 0x7E). I've ...
1answer
41 views

### Calculating the average key search time of DES

I am trying to understand how to calculate the average key search time given a specific scenario: Suppose we have a program that uses standard DES with 56 key bits, and we can test 10^6 keys per ...
0answers
25 views

### Indistinguishability through a chosen plaintext attack

I have a question about how to go about doing an IND-CPA style attack. I'm supposed to think of this as two black boxes, where I do not know which box contains which function. What would I do with the ...
0answers
15 views

### Understanding CPA and CCA Secure [duplicate]

CPA attack means the attacker can send in his own plaintext to the oracle and receives some sort of ciphertext back. CCA attack means the attacker can send in his own ciphertext to the oracle and ...
0answers
24 views

### Performance of Fully homomorphic encryption VS Paillier encryption in Practice

Consider two schemes both have computation complexity linear to the input size (i.e. number of inputs). One scheme is based on Paillier encryption and the other one is based on fully homomorphic ...
1answer
134 views

### About the Security of PCBC Encryption Mode

We are designing an encrypted file system. We plan to use the PCBC (Plaintext Cipher Block Chaining) encryption mode for encryption. This is because we desire the feature ("small changes in the ...
2answers
271 views

### How secure is a pronounceable password in terms of entropy?

There are some strong studies which support the use of pronounceable passwords and multiple tools which provide generation of such passwords. According to this question the entropy of a password ...
0answers
47 views

### How can IND-CPA encryption be identity revealing?

This is problem 10 of Chapter 4 "Symmetric Encryption" (pdf) from Lecture notes by Bellare and Rogaway: An IND-CPA secure encryption scheme might not conceal identities, in the following sense: ...
2answers
601 views

### Is it possible to apply hill-climbing algorithm to Diffie–Hellman?

If Eve intercepts all the values communicated between Alice and Bob in a Diffie–Hellman key exchange, and applies the hill-climbing algorithm to reverse the modulo function, how will the algorithm ...
1answer
69 views

### CP-ABE for threshold cryptography

I would like to know if there is any research work using CP-ABE for threshold cryptography? I want to know also if applying CP-ABE for threshold cryptography would overcome other techniques.
1answer
45 views

### How can I prove I have a certain Facebook account by signature?

I would like to know how to prove I have certain Facebook account (or that I can login to that account).
1answer
54 views

### Bcrypt input length vs collisions

I am currently implementing oauth2 bearer token authentication and am storing the tokens bcrypt encrypted. My question is how long should the tokens be to achieve maximum security. E.g. at what length ...
0answers
17 views

### Data in frequency modulated audio [closed]

I'd like to have a peek at the firmware of a piece of Hardware. Its firmware is available as a .wav file to be uploaded via audio jack. https://drive.google.com/open?id=0B6S_PcWWM1YlQnNwT2FSMnFzVE0 ...
2answers
34 views

### Certificate Path Verification of X509 Certificate

I have the trusted root certificate which I am validating using the self signed key. I also have the intermediate certificate, which i am validating using the root certificate. Now when i am ...
0answers
13 views

### Format Preserving Encryption tool for iOS? [migrated]

I found certain Format Preserving Encryption options in Java (JavaFPE-github) and .net (DotFPE) but none for iOS/android. I am making an app for both iOS and android which would need a common ...
1answer
26 views

### Byte size of Diffie-Hellman public values

I have a scenario that uses RFC-3526's Diffie-Hellman Group 14 for 2048 bit key exchanges. From the document, it specifies the P (prime) value in hexadecimal value as: ...
1answer
36 views

### Is it safe to use MD5 in a proof of work system?

Here is the POW system: you are given a string and you need to compute a suffix so that first few bits of the MD5 value are all 0. I know MD5 is collision vulnerable, but is it safe to use MD5 here, ...
3answers
49 views

### Perfect hash function

Is a perfect hash function always bijective ? In Wiki "In mathematical terms, it is a total injective function" but it does not mean, that it is bijective.
0answers
24 views

### Is a timing side channel attack effective when the leaked information is related to the result of a hash?

I'm writing a function to act as a cryptographic hash of a number within a range that returns another number of the same range. The catch is that the result needs to have certain properties. I run a ...
0answers
15 views

### Does the length of the keyword used for keytable for Playfair matter?

So for Playfair, we choose a keyword and put that in the keytable with no duplicates. Then, we fill the rest of the table with alphabets in order that are not in the keyword without 'J'. Does the ...
0answers
26 views

### ephemeral-ephemeral ECDH and MITM attack [duplicate]

ephemeral-ephemeral ECDH is it susceptible to MITM attack ? if yes, can you please give me a detailed answer ( Workflow that can be followed by the attacker) and how we can prevent this attack ...
3answers
307 views

### Can machine learning analyze random number generator?

I'm studying for random number generators(RNG) and I saw about machine learning a few days ago. So I searched analysis of RNG using machine learning. But I couldn't find such fields. Are there such ...
2answers
51 views

### hash functions preimage and second collision resistance [duplicate]

A hash function H is secure in terms of pre-image resis-tance. Does this imply that H has second pre-image (aka weak collision) resistance?
3answers
159 views

### Is there an upper bound to the private exponent in RSA?

In the RSA algorithm, we choose $p$ and $q$ as prime numbers and we select a value $e$ which is coprime to $\varphi(pq)=(p-1)(q-1)$. Then we calculate $d:=e^{-1}\bmod\varphi(pq)$. My question is: ...
2answers
30 views

### Does SRP also authenticate the server to the client?

The Secure Remote Password (SRP) protocol lets a client prove to a server that it knows a specific password without revealing that password to the server. The server stores a cryptographic verifier ...
2answers
114 views

### lcm versus phi in RSA

In textbook RSA, the Euler $\varphi$ function $$\varphi(pq) := (p-1)(q-1)$$ is used to define the private exponent $d$. On the other hand, real-world cryptographic specifications require the ...
0answers
35 views

### Perfect Secrecy of AES file Encryption

Why does AES file encryption not ensure perfect secrecy? I understand that $\Pr[E(K,M_1)=C_1] = \Pr[E(K,M_2)=C_2]$ given $M1\neq M2$ holds for perfect secrecy of a scheme. However, this seems to hold ...
2answers
30 views

### Is it secure to use TOTP with same key and different time-counters?

If I use TOTP to generate codes with different "expiration" time, using the same key for HMAC, will I create some kind of weakness?
1answer
124 views

### Is it safe to derive a password from a signature provided by ssh-agent?

I'd like to use a password-based system on a remote host (accessed via SSH) without having to copy-and-paste the password and without storing it on disk. Using the system with some other form of ...
1answer
162 views

### Is this variant of SRP for peer-to-peer authentication practical?

I'm interested in using a modified form of SRP as a peer-to-peer authentication method. Since neither side is acting as a host, one of the primary design goals for SRP (that the client doesn't need ...
1answer
38 views

### How is RSA able to prevent brute forcing using the public key?

Bob calculates a private and public key. Bob sends his public key to John. Jeff is a third party unwanted member and manages to snatch the public key mid-transfer. John encrypts his message ...
0answers
18 views

### Cipher that XORs each character with another in the string, using character parity to control the offset

I've reversed the following from a challenge binary I'm investigating: ...
1answer
178 views

Let : $G_{0}$ and $G_{1}$ be two multiplicative cyclic groups of prime order $p$. $g$ is a generator of $G_{0}$ and $e$ is a bilinear map, $e : G_0 \times G_0 → G_1.$ $𝐶_{1} = 𝑔^{𝛽𝑠_{1}}$, $... 4answers 50k views ### Why is elliptic curve cryptography not widely used, compared to RSA? I recently ran across elliptic curve crypto-systems: An Introduction to the Theory of Elliptic Curves (Brown University) Elliptic Curve Cryptography (Wikipedia) Performance analysis of identity ... 2answers 73 views ### Is reverse NTRU still secure? I'm currently prototyping something with the NTRU encryption scheme but I wish to use it in "reverse" -- distribute private keys so anyone can decrypt, but keep the public keys secret and thus only ... 3answers 117 views ### Calculating$\mathbb F_{p^2}$-rational points of an elliptic curve defined over$\mathbb F_p$How can I calculate points on an elliptic curve defined over$\mathbb F_p$, for example$y^2 \equiv x^3 + 1 \pmod p$, with coordinates in$\mathbb F_{p^2}$? (points might have complex number format in ... 1answer 93 views ### Why not to use curve over field of$p^m$with$p > 2$for ECDSA? I'm reading the ECDSA paper and they say you can only use ECDSA with odd-power fields$p$or with binary fields$2^m$. Why not other power prime fields? 4answers 415 views ### Can an encryption method be used as a hash function? As I understand, there are a few requirements for a good hash function. Hard to find any message from a given hash Hard to find any 2 messages which give the same hash A single bit change in the ... 2answers 83 views ### How is message length involved in public/private-key encryption? I've just read this question regarding why to sign only the hash of a message. I kind of understood the answer, but the question arisen is now: Why can I encrypt any text messages with the same ... 1answer 46 views ### How to exctract ECDH parameters from an OpenSSL-generated$G\$?

I'm using ECDH for generating ECDH public parameters (p,a,b,G,n), I try to get this values using openssl ecparam -in cert.pem -text -noout For ...

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