# All Questions

17,953 questions
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### Is it possible to get different plaintext from a single ciphertext using different keys?

I will explain better my question here. Suppose to have a chipertext that you can't decrypt, but you know that the plaintext can be A,B or C. Then arrives to you the key which is used to encrypt the ...
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### How many bits are needed to commit one bit non-interactively in the standard model?

I'm wondering the state-of-art result about how many bits are needed to commit a single-bit non-interactively? I noticed in the paper of Naor's bit commitment: http://www.wisdom.weizmann.ac.il/~naor/...
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### AES_256_ENCRYPT_CTR(key, sha-1(plainText)+plainText) VS AES-GCM, which is more secure?

What if we encrypt sha-1 hash of the plain text, along with the plain text using AES-256 in CTR mode? How much future proof the above method would be in comparison to AES-GCM or any other method ...
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### Does side-channel attacks offer any difficulty to Stinson's concept of provable security'?

Here's a quote from Douglas Stinson: “[i]f a cryptosystem can be ‘broken’ in some specific way, then it would be possible to efficiently solve some well-studied problem that is thought to be ...
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### Is RSA provably secure in the sense of Douglas Stinson's `provable security''?

Here's a quote from Douglas Stinson: “[i]f a cryptosystem can be ‘broken’ in some specific way, then it would be possible to efficiently solve some well-studied problem that is thought to be ...
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### Estimate Security level of the Rabin Signature

I'm trying to figure out how long the modulus $n$ has to be in the Rabin Signature scheme, to provide 128 bit security. We assume that the used hash function is "secure enough". Then the naive ...
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### SSL - encrypt with private key and then with public key?

Say there are 2 sides that wish to communicate: side A and side B. Let's say we are looking at side ...
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### Is it possible to generate same RSA key on purpose?

I want to ask if I have a RSA private key can I use it to generate RSA key that is identical. If yes how can I do it?
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### Hash Collision Probabilities

Please give help! how can I calculate the probability of collision? I need a mathematical equation for my studying. Assume, I am using SHA256 to hash 100-bits. Thus: SHA256 {100} = 256-bits (hash ...
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### The goal, the method, and the interface of the signcrypt primitive.

Some time ago, I proposed making the site more educational by teaching correct cryptographic programming. The proposal had had somewhat good reception, but was met with cold ice as there had been ...
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### What are the curly brackets in this cryptographic hash function definition?

Reading the Schnorr signature Wikipedia page, I stumbled upon the following statement: All users agree on a cryptographic hash function $H:\{0,1\}^*\to\mathbb{Z}_q$. What do these curly brackets ...
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### Is this device authentication method (using AES-256) secure?

Let's say we have: client_id_ran: 256 bit random text (chosen only once for whole system) used to generate client_id by ...
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### Decrypting ciphertext that is missing a block

In the AES encryption, suppose that the key is known. The ciphertext is also known except for a block of the same size as the key. In the worst case scenario for the attacker, how hard is it for ...
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### Given a particular $1600$-bit output $Y$, is it feasible to find a $1600$-bit input $X$ such that $\text{Keccak-}f[1600](X) = Y$?

I have read this answer on Crypto.SE and I want to clarify a few details. Does this property of $\text{Keccak-}f[1600](x)$ imply that if we know a particular $1600$-bit output $Y$, it is feasible ...
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### Can you tell how many times data has been encrypted?

I'm using multiple RSA keys to encrypt a piece of data. The data length is constant but the data itself is not. Each time I encrypt I prepend a 64 bit string to the newly encrypted ciphertext. This ...
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### Can we find the exact number given remainder of the numbers with mod m?

I have around 1500 numbers. The numbers $x_i$ are calculated as $x_i$=($p*t_i$) mod m. $p$ constant and same for all the numbers while $t_i$ are chosen randomly everytime. For example the given ...
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### RSA restore part of D from E and N

I have full bits of public key $(n,e=65537)$ but from the private key, I have the lower half bits of $d$. Can I restore the whole RSA private key from that data and use it for decryption?
I am trying to solve this exercise. Assume an oblivious transfer protocol that uses a trusted third party Trent. Alice's messages $M_0$ and $M_1$ are binary values of length $k$. Bob's message ...