# All Questions

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### Is a tweakable block cipher still considered deterministic in nature?

"a block cipher is a deterministic algorithm operating on fixed-length groups of bits, called blocks, with an unvarying transformation that is specified by a symmetric key. - Wikipedia " But with a ...
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### Diffusion in Shamir's secret sharing scheme

The popular command line utility ssss implements the classic Shamir's secret sharing scheme over the generic field $GF(2^q)$ with $8 \le q \le 1024$. When $q>=64$, the constant coefficient ($c_0$) ...
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### XORing a header with SHA512-hash - secure?

I am writing a application that encrypts text several times and stores the result. The result looks like complete random bytes, therefore I add some random bytes at the end. To let the program know ...
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### Cryptographic library quality [on hold]

I've been working on a project that will require secure communication over the internet, so I've been thinking of TLS 1.2. After looking around I chose Botan but then I thought about using a more ...
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### How to calculate Modulo using a standard calculator for a one time pad encryption

I wrote a simple python script to preform one time pad encryption I would like to be able to decrypt the ciphertext by hand. In my script I use mod 26. This is how I was shown to calculate a mod ...
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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 [on hold]

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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### 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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### Decrypting a small Message using RSA with a Private Key [on hold]

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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### 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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### 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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### 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 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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### The relationship between the key length and encrypt time in Xor algorithm?

I did work on the encryption algorithm and the decryption using the XOR method noticed that when more the key length, the less time spent on encryption and decryption. I have two questions in ...
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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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### 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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### 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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### 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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### 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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### 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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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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### 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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### SHA256 Padding and Parsing [closed]

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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### 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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### What is a 'secret key factory'? What precisely is it doing? [closed]

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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### 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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### 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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### Certificate Revocation List [migrated]

There are many fields on a certificate revocation list (CRL) like Algorithm, Parameters, Issuer Name, This update date, Next update date, user certificate serial #, etc. While I understand the purpose ...
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### Exchanging Keyspace and Message space in PRF

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 ...
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### does re-encrypting the same value with multiple keys reduce security

I found myself wondering today, how much security is lost if you take a plaintext - assume that its content, including any metadata is unknown to an attacker, for example it may be random data - and ...