# All Questions

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### Encoded Output to ASCII for carving into objects. [closed]

I have a piece of text that I need to carve out into an object after some encryption. For this purpose it works better if I have alpha numeric output instead of with any special characters (like I get ...
68 views

### Should I add randomness at the end before AES?

Seen AES, changing a character drastically affects the ecrypted text. I want to make it harder to decrypt AES I send. So, it seems this can be done by adding some special code and some random bytes ...
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### Need for 3 rounds in Luby Rackoff theorem

I get that using Feistel network we can create a secure PRP from a secure PRF (in 3 rounds according to theorem). My question is why not just 2 rounds of Feistel network is sufficient. Is it that ...
733 views

### Does a big salt have the same memory effects as Bcrypt?

Citing Thomas Pornin on the question Why can't one implement bcrypt in Cuda?: bcrypt is a variant of the Blowfish key scheduling, which is defined over a table (a few kilobytes) which is ...
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### Blind_signature.How it works [closed]

The technology of using blind signature. How it works imitating the coins?
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### AES GCM encryption, authentication and PBKDF2

I'm developing a kind of secret vault server application. The basic principle is similar to DPAPI where each secret will have its own unique random KEY/IV pair and and that KEY/IV pair will be ...
247 views

### AES 128 bits with 12 bytes IV vector composed of a 4 bytes counter : safe?

I have a 128 bits AES cypher (GCM, Galois/Counter Mode) using a 12-byte initialization vector (IV) composed of: 8 constant bytes: 6 bytes (device ID) 2 bytes (zero) 4 bytes (incrementing frame ...
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### openSSL TDES DECRYPTION [migrated]

I have a tool which is using openssl for RSA and DES/TDES operation. After processing by a tool, I got key = 4F324364970DBA5DE058EF0EAE54625E and the encrypted data ...
432 views

### What is the random tape?

I am reading the paper "Toward plaintext-aware public-key encryption without random oracles" by Bellare and Palacio. So I can't understand what is the tape and random tape?
53 views

### How to calculate the exponent in modular exponentiation?

I have a problem when calculating power in modular, $a^b \bmod c = d$. where we can know values of $a$, $c$ and d, but we don't know values of $b$. example : $29^b \bmod 1024 = 365$. So, how can I ...
68 views

### How do I validate the AES cipher?

I have used AES CTR mode of operation. Each time a file is uploaded an encrypted file is obtained and the corresponding cipher is got – this is a mini project I have done. I wanted to know so as to ...
35 views

### FHE Block ciphers' usage

There are currently FHE implementation for AES Simon Speck, and may be more. Except for speed testing, amortized or not, one meaningful usage is mitigating form side channel analysis. Intel, AMD, ...
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### RSA 3072 is 65,536 more difficult to factor than 2048?

If RSA 3072 is equal to 128 bit symmetric and 2048 is equal to 112 bit symmetric then 128-112= 16 and 2^16= 65,536. In that case wouldn't this make 3072 more future proof against quantum computers or ...
185 views

### How to assess the strength of the avalanche effect for AES?

Within the scope of a study project I'm looking for an approach to assess the quality of AES encryption in practice. To do so, I modified the OpenSSL source code to be able to log metrics while ...
25 views

### How to add passphrase to an RSA key?

If I want to protect a private RSA key, do I just XOR the password into the key, or do I do something else? Is it secure? Edit: I got a good answer from a comment - Hash the password/passphrase with ...
26 views

### Cracking vigenere of non-text cleartext

I've begun a course in crypto on coursera and the first homework was writing a vigenere(xor) cracker. It works, which was a rush :) but it makes one core assumption, one has encrypted a natural ...
82 views

### Generating an IV for AES-CBC

I am faced with the task of generating a secure 256-bit IV for AES-CBC. I possess the following resources: A 32-bit microprocessor A 32-bit PRNG (can read/reseed) A 64-bit clock counter (can read) ...
194 views

In one of the hot forums of today on how to convince friends cryptography is good one of the arguments stated is the knife paradox, I was unable to find the answer on Google and my question is what is ...
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### Cryptanalysis of XOR cipher with repeated key phrase

My assignment is to cryptanalyze cipher text that we know was encrypted with a stream cipher (bitwise XOR of plain text and key stream), and decrypt to plain text. We know the key stream is a repeated ...
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### Can one make a secure AEAD from any secure cipher and any secure MAC?

Can one make a secure AEAD from any secure cipher and any secure MAC using encrypt-then-MAC: with independent keys and IVs (any cipher and MAC) if the cipher is a stream cipher (including a block ...
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### Is there a reduction of security if I XOR Pkcs5S2 and SecureRandom?

I'm using this codereview sample to encrypt data. I would like to provide hardware protected encryption and a user password as the key. Is it acceptable to XOR the KDF Pkcs5S2 in Bouncy Castle with a ...
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### Is the one-time pad secure?

I have read about one-time pads (OTP) on Wikipedia. Is this secure? Can I actually use modular addition as ecryption like it said in Wikipedia? And the plaintext is as long as the OTP, so when I send ...
21 views

### private-key can't be traced (GPG)?

I am very new to cryptography. I was reading about GPG/PGP Basics, and I have a doubt: As per my understanding, Everyone knows the algorithm (GPG) with which I generated my key pair. And If I give my ...
39 views

### Key exchange problem

I've found the following problem in one of my courses. Any tips on how to solve this would be appreciated! Alice has the key pair $(pka,ska)$. Bob has the pair keys $(pkb,skb)$. They want to ...
20 views

### MAC-then-encrypt: Using one-time-MAC with randomized CTR

The Coursera cryptography 1 course says: If you want to use MAC-then-encrypt mode then you should either use randomized-CTR or randomized-CBC. And if you use randomized-CTR then one-time-MAC ...
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### Fixed initialization vector in aes cbc [duplicate]

What are the pros and cons of using fixed iv in aes-cbc encryption? I've read somewhere that it said using fixed iv doesn't really matter?
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### Randomness of a Key in a One Time Pad

The keys used in an One Time Pad are required to be randomly generated from a keyspace $\mathcal{K}$, we require 256 bit random keys, i.e. $\mathcal{K}=\{0,1\}^{256}.$ Suppose we randomly select an ...
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### Is $E′(k,m)=E(0^n,m)$ semantically secure?

$(E,D)$ is a (one-time) semantically secure cipher where the message and ciphertext space is $\{0,1\}^n$. $E'(k,m)$ is defined as $E′(k,m)=E(0^n,m)$ The question is whether $E'(k,m)$ is (one-time) ...
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### Application level encryption and key renewal

I had posted this question on stackoverflow and been asked to move it to crypto. What is your view on this? What is the doability? I have a question related to encrypting data in the database, at the ...
30 views

### Is a good idea to generate a public key from a secret key using a functional encryption scheme?

FE - functional encryption PK - public key I want to design a PK cryptosystem that has a unique PK for each encryptor. Namely, the encryptor submits a unique value (or an attribute) to the private ...
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### Why there is time period of key pairs in public key cryptography? [migrated]

In Public Key Infrastructure, every key pair is associated with its life time. I don't understand why we have a life time when we have functionality such as certificate revocation list(crl) which ...
28 views

### Why would a 3DES key decrypt one block, but not the next?

I'm trying to crack an encrypted data stream. It appears to be using a 64-bit 3DES key (as written in the application logs), and in fact using that key does correctly decrypt the first 64-bit packet ...
20 views

### Is ISAAC vulnerable to a cache timing attack?

Is the ISAAC stream cipher vulnerable to a cache timing attack in efficient implementations? It seems like it would (secret-dependent array lookups) but is it exploitable in the context of ISAAC?
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### Can the weak states in ISAAC be used for an attack?

Can these weak states in ISAAC be used for an attack? They have some of the 256 words equal to each other. There are a lot of them, but the weakest are rare and most of the biases (all of them for ...
21 views

### Is a KDF needed when using X25519 for ECDH and XChaCha20-Poly1305 for AEAD?

Is a KDF needed when using X25519 for ECDH and XChaCha20-Poly1305 or XSalsa20-Poly1305 for authenticated encryption? My hypothesis is "no" because the key from X25519 is less than 256 bits long; ...
33 views

### Get secret_value from multiple hashes md5(known_value_n + secret_value) [duplicate]

The attacker knows multiple hashes like md5(known_value_n + secret_value), for multiple known values. Does it help him to discover secret_value better then just single md5(known_value + secret_value)? ...
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### New Improved Probabilistic version of RSA

On the 2nd page of "New probabilistic public-key encryption based on the RSA cryptosystem" by Roman'kov (PDF), at last it says Alice can find "f" of order "l" with least probability of (1-1/l). I ...
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### How to normalize data of a generic HTTP request for the purpose of signing

I am working on PowerAuth 2.0, a solution for counter-based signing of HTTP requests (for the purpose of mobile banking). One of the tasks that I solved somehow but I am still not happy with the ...
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### Probability of IV/key reuse

I generate randomly both an initialization vector (IV) and a symmetric key (key) to feed an authenticated encryption scheme. How much IV/key combinations can I generate until the same combination ...
30 views

### Has anybody implemented BGN cryptosystem to multiply two plain texts?

I have tried to use this code as follows, http://stackoverflow.com/questions/33581962/bgn-implementation-in-java but the issue is, when it generate the pairing, the output is in GTfiniteelement (for ...
51 views

### Get $a$ such that quadratic residue has a solution (Rabin)

My task is to implement Rabin signature. I have trouble with choosing padding a such that $$x^2 \equiv a \pmod n$$ has a solution. In that context, $n=p\cdot q$ is composite, where $p$ and $q$ are ...
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### What's the difference between PBKDF and SHA and why use them together?

I've been reading a little bit about hashing lately and according to AgileBits, they use "SHA512 within PBKDF2" in their new vault file. I've looked in Wikipedia for both names and I know PBKDF2 is a ...
53 views

### Fixed primes in discrete logarithm

The discrete logarithm problem is to find $z$ when the inputs are $g,h,p$ where $g^z\bmod p$. Supposing if you fix $p$ then does the problem become any easier to attacks and is there a $(\log p)^c$ ...
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### How do you work out the private key in a RSA cryptosystem knowing a certain public key?

The public key: n = 85 and e = 19 I know that n is the product of two prime numbers, now is it right of me to figure them out by process of elimination which I got p or q equals 17 and 5. Or is ...
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### Effective ways to find partial sha1 collision [migrated]

I need to find 2 different string and compare their hash value. Both string must contain "abc". I looking for the first eight character that are the same and stop. I have been running for more than 24 ...
54 views

### Difference between FleXOR and Free-XOR

I would like to know the differences between FleXOR and Free-XOR. I searched in the web but I couldn’t understand the information I found. I understand that there are both cryptographic methods as ...
56 views

### Zero Knowledge Proof extended Schnorr - average secrets

I am trying to compute and an overall average number of given secrets from inside the commitments. I have the following set-up: Three commitments; \$C_{1}(id, num, r) = g_{1}^{id} g_{2}^{num} ...
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### Is the following 4 digits code generator secure and non-deterministic?

In a C# WCF service, I need to send a 4 digits code by SMS to validate a user account/password. For security reasons, the code has to be non-deterministic (so that a malicious user/hacker should not ...
I have access to an oracle that can encrypt and partially decrypt a number with RSA-1024 algorithm. For encryption: $$C = M^e\bmod n$$ But for decryption, result will ...