# All Questions

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### Pseudorandom number generators based on hard problems in mathematics

I know that Dual_EC_DRBG's security is based on the ellitpic curve discrete logarithm problem, Micali-Schnorr is based on the difficulty of factorization, and MQ_DRBG is based on multivariate ...
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### Questions about updating the secret key of RSA?

I want to update the secret key of RSA. I understand there exists a common modular attack on RSA. Precisely, if adversary knows $(e_1, m^{e_1})$ and $(e_2, m^{e_2})$, where $e_1$ and $e_2$ are the ...
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### Alternative sources of random numbers

Considering that algorithmic methods for generating unpredictable streams are hard to come by, I've wondered if any of these potential sources are good for making keys, seeds, and the like: stocks, ...
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### How does the attacker include input before compression and encryption in CRIME?

I have read this article about the CRIME attack against TLS and SPDY. The article says that: What is not yet clear is how the attacker is including their input in the source material before it ...
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### Requirement for the exponent generation during DH protocol [duplicate]

The setting is classic DH protocol. Alice computes $A = g^a \bmod p$. Alice then sends $A$ to Bob. Then Bob will send $B = g^b \bmod p$ to Alice. Are there any requirements for the values $a$ and $b$...
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### Crypto++: How to re-generate pseurandom integers in Crypto++

I'm using Crypto++ to implement my protocol to mask a value $y_i$ by a seudorandom value $r_i$ such that $m_i=y_i \cdot r_i$. Since there are many $r_i$'s I want to generate them using PRG and then ...
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### Counter Mode (CTR) and mult-CPA

I am not sure if Counter Mode (CTR) encryption is mult-CPA (chosen-plaintext attack) secure or not.
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### Is Pseudo-Random Generator (PRG) in OpenSSL uniformly distributed?

I need to know can we use PRG of OpenSSL as a PRF?
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### Explanation of each of the parameters used in ECC

I'm having a very difficult time finding a clear explanation of the parameters used elliptic curve cryptography. I know for certain that $p$ is the number or order or whatever of the given field that ...
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### Hashing - Digital Signing and Trivial Stretching

Two very basic questions: 1. Digital Signing Why is it not possible to just simply replace the hash value from the request? Examples: ...
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### Can we say that if $P=NP$ there is no CPA secure public key encryption?

I've learned that public key encryption is based on the problem of Discrete Log (as regard to group theory) which believed to be hard. But, can we say that it doesn't matter on which problem our ...
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### McEliece information set decoding attack vulnerability

Wikipedia states that McEliece is open to "information set decoding attack". What is an "information set decoding attack" and how serious is the vulnerability? (is it just a matter of choosing proper ...
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### Does key derivation with known parameters add any security?

First up: this is a question about a concept that I try to wrap my head around; it is not about the specific implementation. Anyway… I have the following scenario (simplified to show the problem I ...
183 views

### Malicious DH groups

Can an attacker construct a DH group, large enough to be considered secure (say, a modulus of 2048-bits), such that the group appears safe, but the attacker is able to solve the DLP in the group ...
488 views

### What is the forward cipher function of AES-XTS?

We're using OpenSSLs EVP_aes_265_xts encryption on data (with unique, random, IVs for every new message encrypted) - which is working well. But, I've been asked; what is the forward cipher function ...
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### Text in random image encoder: is it flawed?

I have created a small cryptographic programme: You input your text A random image is generated Random coordinate pairs in number equal to the chars of the message are generated. The red component ...
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### Analogue encryption algorithms

I have a basic understanding of how strong encryption works on digital data. Bits can be changed so that they appear completely random and map one-to-one back to the original set, given the correct ...
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### Pseudorandom function library [closed]

I'm wondering if there is any library supporting pseudo-random function, so I can specify the key length and output domain. Is it correct that I need to use a block cipher for this purpose? Any ...
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### Why not just encrypt the message and the hash of the message to achieve cryptographic integrity? [duplicate]

I've always seen MACs as a way to provide integrity and authentication. You would just append it to some message in clear. But this is clearly not the case when you're doing Encrypt Then Mac. When ...
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### Diffie-Hellman Application

Alice and Bob want to perform a Diffie-Hellman key exchange using the group $G$, a primitive root $g$, Alice’s secret key $k_A$ and Bob’s secret key $k_B$. In each case below compute the element of $G$...
657 views

### CBC-MAC: is it secure to authenticate a fixed length ciphertext?

Suppose I have a fixed-length arbitrary ciphertext. To authenticate such ciphertext: I generate a random AES Key $K_{auth}$. Then I compute the CBC-MAC Tag of the ciphertext with $K_{auth}$. ...
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### Security of SecRandomCopyBytes on OSX and iOS

How secure is SecRandomCopyBytes() (Apple's RNG)? Has anyone ever reviewed it?
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### Is the key deducible with AES CTR when we know about the plaintext, IV and the ciphertext? [duplicate]

Simply as stated, with AES running in CTR mode, can somebody work out the key (without brute-forcing) given we know about the plaintext, IV and also the ciphertext. Assuming we also know about the ...
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### Check if this cryptosystem is safe

Let $G$ be any group where group operations, as well as finding the inverse of an element, can be performed quickly, but the discrete log problem is difficult. Consider the following cryptosystem: ...
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### 3DES Modes EED orEDE?

Can we use EED with 2 keys (K1 K1 K3) rather than EDE (k1,k2,k1) ? We measure the strength of DES by the effort (in term of number of tries) in finding some K1 & K2 to match a known plaintext and ...
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### what is PFS game?

when i reading about this paper, in the Setup of SIM section 5.2, it says that "According to the definition of PFS game", i wonder what the definition of PFS game ...
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### Why does NaCL have different keys for signing and encryption?

I want to start using NaCL to sign messages that will go into a message queue, and I noticed that it generates different keys for each operation. Is there a reason for this? Can I not use the same PK ...
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### Self changeable key [closed]

If key changes itself when it send/receive message what would be could breaking method? So: $E: m×k$ in which $k$ is last generated key $D: c×k$ in which $k$ is last generated key $k{_n} = k_{n-1}×m$...
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### Strategies for securing public key storage on software

I´m kind of new in this so I apologize in advance for any noob mistakes (feel free to point it out) We are developing a licensing mechanism on our software, and I would like some advice. The ...
175 views

### Save the last cycle in GCM GHASH calculation

I need to implement GCM GHASH in hardware, using FPGA. The data bus is 640 bits, so I will use 5 adder/multiplier blocks in parallel. The message size is fixed and AAD is 0. A little example: ...
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### Is the idea of a known plaintext attack really that new?

As you can probably guess, I just watched The Imitation Game, which hasn't really gotten points for historical accuracy... During World War II, Turing and his team fret that they can't know the ...
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### FIPS-Compliant SHA2

I want to use SHA-512 for hashing in a system that must be FIPS-compliant. When I look at the FIPS 140 list of approved providers, I don't see SHA from any provider as being an approved algorithm, I ...
175 views

### Deriving a decryption equation

Consider a very simple symmetric block encryption algorithm, in which 32-bits blocks of plaintext are encrypted using a 64-bit key. Encryption is defined as C = (P⊕KL)⊗KR where C = ciphertext; K = ...
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### Testing the Fortuna random number generator?

I have implemented the Fortuna random number generator as described in chapter 10 of "Practical Cryptography" (Ferguson and Schneier, Wiley, 2003), the result can be found at http://www.seehuhn.de/...
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### Prime modulus for RSA and sharing a secret?

According to this paper entitled "Using Commutative Encryption to Share a Secret" they define their modulus to be a large prime p, which is public. Both exponents are private in this case. According ...
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I have a secret message which I want to encrypt such that any of several different keys can open it independently. The keys can't know about each other and it has to be able to work completely ...
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### Key establishment protocols other than Diffie-Hellman

Are there any key agreement/exchange/establishment protocols which are NOT based around the Diffie-Hellman protocol or handshakes using public key cryptograaphy? DH seems to form the basis of this ...
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### Hash function as secure as one-time pad?

We know that the one-time pad is provably secure as a cipher to encrypt some data. Is there an algorithm which does the same just as a hash function? Can we get a provably secure hash function? Maybe ...
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### Identity-Based Encryption consist of four algorithms. Extract phase is one of them and it is done by PKG or receiver?

The Identity-Based Encryption consist of four randomized algorithms: Setup, Extract, Encrypt, Decryption. The Setup phase is done by Private-key generator, Encrypt by sender and Decryption by receiver....
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### Storing AES encrypted RSA private keys on a server

I'm thinking about creating an encrypted messaging web application where users create RSA key pairs, they store the public key on the server for others to see and also store an AES encrypted private ...
### Finding $x$'s parity in the discrete log problem
Suppose $p$ is prime, and $g, a\in\mathbb F_p$ are given elements with $g$ a primitive root. The discrete log problem poses the task of finding an integer $x$ such that $g^x=a$. Show that even if $x$ ...