# All Questions

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### What does it mean when two encrypted files, encrypted with the same method but with different keys, when xor'd together, produce a repeating pattern?

Let's say I have fileA and fileB, both encrypted somehow, but in the same method with different keys. If I xor them together, they will make a repeating pattern of 32 bytes length. What does that ...
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### ECDSA verification is too slow

I found that ECDSA is too slow while verifying signatures; can you tell me why? I'm planing to speed it up, so what tips should I consider to make it fast?
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### How vulnerable is the C rand() in public cryptography protocols?

I just learned about the basics of public cryptography a few weeks ago and I am curious as to why the C rand() function should not be used for crypto schemes. For example, say I want to generate a ...
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### Decrypting a small Message using RSA with a Private Key

If I have a private key of (43, 341), what would be the steps I need to take to decrypt a small message using RSA. I have looked ...
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### RSA algorithm , decrypting a message [on hold]

I have to decrypt a message (24-264-291-291-220) using RSA algorithm given the private key. I did all the calculations and the decryption of that message is 74-66-48-48-55. My question is how would I ...
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### Client-server authentication protocol suggestion [migrated]

I'm designing an authentication methods for my client/server system consisting of: a windows desktop client application (.NET) windows/linux servers (C++) one "security server" which authorizes the ...
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### RSA and ECDSA algorithms [on hold]

Hi, i want to learn more about ECDSA and RSA Digital signatures , could you give me both Algorithms for sign and verify the data.
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### One time pad: why is it useless in practice?

The symmetric cryptosystem One time pad (OTP) seems to be very beautiful since it is perfectly secret according to Shannon. Many books, however, point out that the main drawback is that one must ...
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### mathematical derivation for elliptic curve cryptography [on hold]

how to derive the mathematical derivation for elliptic curve cryptography,please to send full detail derivation for elliptic curve cryptography,and also i need how to use the galois field in ...
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### Is it possible to forge elgamal in a determinsic way? [on hold]

El Gamal is existentially forgeable, would it be possible to forge it in a deterministic way ,i.e., eliminating the randomness? Maybe by using fermats little theorem ?
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### Is ElGamal still unforgable if the adversary knows r

Is ElGamal still unforgable if the adversary knows the value of $r$ that was calculated by $g^k$? When we do sign the message $msg$, we calculate $r = g^k$. As we know the regular ElGamal ...
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### Using Stream Cipher as CSPRNG

Are there any guidelines or justification for converting a stream cipher algorithm for use as a CSPRNG? For instance, lets say I wanted to convert one of the eStream portfolio Profile 1 (software) ...
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### Is there a method to combine encryption and ring signing?

There's the well-known question on whether to sign or encrypt first. However, if instead a message is to be ring-signed such that either recipient could be the actual signer, is there any scheme that ...
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### Do Chosen-Chiphertext attacks only apply to public-key cryptosystems?

Do Chosen-Chiphertext attacks (CCA-1/2) only apply to public-key Cryptosystem?
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### Is it possible to crack any MD5 hash? [on hold]

I really wonder is it possible to crack any MD5 hash?
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### Turning a cipher into a hashing function

This is theoretical question. I'd like to know if it's possible (and what are eventually the consequences), not that I'm going to do it in one of my projects. ;) The first hashing functions created ...
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### Is the strength of RSA over quadratic or other cyclotomic fields as strong as over the integers?

If we assume the strength of RSA is based on the difficulty of factoring (which I know we can't guarantee) and we compose the modulus of some other quadratic ring that is a unique factorization domain ...
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### Would usage of jCryption 3.0 + SSL have mitigated the Heartbleed vulnerability? [migrated]

I came across a project called jCryption 3.0, which encrypts data between the client and server, without using SSL. If a website's JavaScript had used jCryption 3.0 to encrypt login form fields before ...
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### How can I convert numbers into prime numbers?

I'm working with one-way accumulators, but I'm not knowledgable in cryptography. Is there an easy peasy way to hash numbers (or whatever) into prime numbers? Obviously I'd like it to be collision ...
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### What happens if biometric data is stolen? [migrated]

This question isn't very specific, but I think it would be ok to post it in the cryptography StackExchange (hopefully). As we move toward a future where fingerprints might possibly replace passwords, ...
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### Existence of a map $\phi:\mathbb{Z}_{N^2}^* \mapsto \mathbb{F}$

Is there a map between the group of $\mathbb{Z}_{N^2}^*$ where $N$ is a composite number , a product of two equal size secure prime numbers $p$ and $q$ and a finite field $\mathbb{F}$, such that for ...
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### Composing hashes and/or MACs

Suppose I have n hash/MAC functions, of which n-1 are extremely insecure, leaving only one that is in fact cryptographically secure. If I use all of them on a message and the XOR them together the ...
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### Is anyone aware of Du atallah multiplicative secret sharing scheme for dot products for > 2 party scenario?

I am working on Du Atallah's multiplicative secret sharing scheme for more than 2 party scenario. Is anyone aware of its multiparty version (more than 2 parties). The paper for 2 party can be found ...
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### Which commitment scheme is better for malicious models [on hold]

Can some one suggest which scheme is better for malicious models in terms of efficiency and security? A Pedersen's VSS based scheme or the one based on Fiat-Feige-Shamir digital signatures ?
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### SSL-like protocol with public-key hard-coded in the client

Imagine a SSL-like protocol that instead of using certificates signed by a trusted CA, has the server's public key hard-coded in the client. My question is: what happens if the server's private key is ...
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### Sequence of Encrypting RSA like Chaum Blinding scheme

I'd be a noob in cryptography but reading up a little on RSA, I do get some understanding and I want to specifically resolve this issue. UPDATED Lets say we have the following values in place: ...
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I am creating a database to store our client's information at work (a heritage center specializing in DNA based genealogy. Once the results of a test come back we have people that use the information ...
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### Has there ever been more then a theortetical difference between preimage resistance and second preimage resistance?

In other words, has there ever been a point in time in which having the content of a message has actually helped break a hash function?
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### Are AES-256's related-key weaknesses exploitable if it is used to build a hash?

Assume it is made a hash based on AES-256 encryption (perhaps because this is hardware-accelerated, but no standard hash is); and it is used the Merkle–Damgård structure, that is padding of the ...
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### SHA256 Padding and Parsing [on hold]

Can anyone please help me with basic Verilog Structure for Padding and Parsing stages of SHA256. I have Googled it a lot but couldn't find it. I'm stuck at How to check the Size " L " of the random ...
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### Are there any elliptic curve asymmetric encryption algorithms?

RSA offers the functionality of encrypting (short messages, or symmetric keys) with a public key, and decrypting with a private key. However, RSA key generation is extremely expensive, especially for ...
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### Leak-proof protocol: is such a thing possible?

Is it possible to design a protocol that by itself guarantees that a malicious implementation cannot leak secret data without breaking the protocol? Setting: Alice and Bob have a pre-shared secret ...
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### Block cipher and parity of permutation

Can anyone explain the following text passage to me? Most real-world block ciphers build even permutations, because it's hard to build odd ones using small operations (32 bit) on larger (128 ...
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### Could program verification techniques prevent bugs of the genre of Heartbleed from occurring? [migrated]

On the matter of the Heartbleed bug, Bruce Schneier wrote in his Crypto-Gram of 15th April: '"Catastrophic" is the right word. On the scale of 1 to 10, this is an 11.' I read several years ago that a ...
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### Does AES-128 have the same strength as AES-256 with a padded key?

When I use the same 128-bit key for AES-128 and AES-256 with a known/public padding for the latter, is there some weakness in AES-256 that is not present in AES-128 with essentially the same key? ...
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### Is there a simple zero knowledge proof of $x$ for $b=x^x\pmod p$?

We have a multiplicative cyclic group $G$ which is a subgroup of $(\mathbb{Z}/n\mathbb{Z})∗$. There are two parties, Alice and Bob: If: Alice knows: $b$ and $x$ such that $x^x = b$; Bob knows: $b$. ...
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### Does IKEv2 protocol have two modes like IKE

IKE Protocol have 2 modes, that modes have different structure. Does IKEv2 protocol have two modes like IKE.
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### Positioning of keys in encrypted text

I'm just looking at very simple encryption. I've noticed that the key is typically either at the front or at the back of the encrypted text. This is quite easy to break if you know the key. It can ...
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### Why does HMAC need a fixed length padding?

As everybody knows in order to calculate HMAC we have to concatenate padding to the message. I am just curious why the padding needs to be fixed-length. Why do we need the blocksize parameter here? ...
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### What is a 'secret key factory'? What precisely is it doing? [on hold]

I have found a Java implementation of AES CBC mode that runs in Netbeans. The lines below appear to create the key from password and salt: ...
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### Security of RSA for paranoids with padding?

RSA for Paranoids (RSAP) (in cryptobytes v3n1), also known as Unbalanced RSA, is a variant of RSA proposed in 1995 by Adi Shamir, as a mean to increase the RSA public modulus size while keeping ...
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### Attack of an RSA signature scheme using PKCS#1 v1.5 encryption padding

My best interpretation of this question is that Java's crypto API has been subverted to perform RSA signature using PKCS#1 v1.5 encryption padding. Assume the signature $S$ of a message $M$ is ...
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### security in the standard model → random oracle model?

Can a protocol proved secure in the standard model be considered secure in the random oracle model?
Suppose there is a secure PRF $F: K \times X \to Y$. Then is $F': X \times K \to Y$, defined by $F'(x,k):=F(k,x)$, a secure PRF? In my opinion it should be because exchanging the keyspace with ...