# All Questions

18,648 questions
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### SHA256 Message schedule function and examples

I'm trying to implement the SHA256 algorithm in python. It is not working. I think the first problem that occurs is with the function for creating words 17-64 in the message schedule. I looked at this ...
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### RSA calculate public exponent

Suppose I have two messages $m_1$ and $m_2$ as well as $c_1$ and $n$. It's standard RSA so $c_1 = m_1^e \ mod \ n$, $c_2 = m_2^e \ mod \ n$. Further assume the only information we have about e is that ...
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### Miners and the calculations to create bitcoins

i'd really like to know in detail the tipe of cryptographic elaborations miner do to generate bitcoin. Can someone help me? Thank you very much.
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### Revoke user ID from revoked gpg key?

Being a total gpg noob, I fooled around generating keys on my ubuntu pc and copying those keys to the OpenKeychain phone app. I managed to successfully revoke a key from the app, so now that key sits ...
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### How to generate a unique numerical value for an alpha-numeric string?

I need to create a unique numerical value for every alpha-numeric string input. Size of output numerical value can be of any size like 32, 64 128 bits. The input string will always be a mongoID type ...
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### Is there any way of decrypt ciphers without sharing the key? [use case IoT]

in symmetric cryptography, key sharing is a big issue. suppose in a IoT environment, the nodes will encrypt a message with the encryption key and receiver need that key to decrypt the message for ...
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### RSA -Diffie-Hellman [on hold]

problem1: The security of the RSA encryption approach relies mainly on the difficulty of the prime factorization of large integer and the difficulty of calculating the Euler Totient function of large ...
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### one time pad cryptography [duplicate]

For One-time pad, it is required to never reuse the same key to encrypt two different messages. Suppose that Alice ignored this recommendation and decided to reuse the same key to encrypt two messages ...
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### Key Reduction in symmetric cryptography

The number of keys in a system with $n$ users where every possible pair of users desire to securely communicate between themselves using symmetric cryptography is $n(n−1)/2$. Is there a way to reduce ...
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### Simulator in the ideal world computes the proof for parties for $F_{NIZK}$

In the definition of $F_{NIZK}$ in [GOS06b], on receiving prove from a party, the functionality forwards the statement to the ideal world adversary $S$. This ideal world adversary then creates a ...
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### Is it possible to recover the key to a decrypted file? [duplicate]

Is it possible to recover the key to a decrypted file if you have the initialization vector and it uses RijndaelManaged in CBC mode? If so how? The file I want to recover the key from is a xml that ...
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### Finding a base of an exponent in mod field

I have the following equation: $$base^{exp} = number \pmod n : base,exp \in \mathbb{N}$$ and another known fact is: $$gcd(base, number) = 1$$ $$n = 2^{2048}$$ base=...
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### Discrete logarithm with exponentiation oracle

Suppose $(n, d)$ is an RSA private keypair. We know the public key only (wlog suppose it's $(n, 2^{16}+1)$ and we are given oracle $E$, decryption oracle for $(n, d)$. Is there any efficient algorithm ...
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### Prove if AES, DES, Pseudo OTP are valid symmetric cipher [on hold]

Could somebody give me mathematical proof if AES, DES, Pseudo OTP are valid symmetric cipher? Basically, I want the mathematical explanation of the encryption and decryption steps so that decryption ...
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### How will be cipher selected when Client is running on version TLS 1.3 and server is running on TLS 1.2?

How will be cipher selected when a Client is running on version TLS 1.3 and server is running on TLS 1.2 knowing that cipher list provided by TLS 1.3 client will be different than the version ...
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### Regarding the isogeny path problem

Given two elliptic curves, it is hard to calculate an isogeny of large degree between them. Does this only apply to supersingular isogenies or to ordinary ones as well? Additionally, is the mapping ...
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### How to understand Authenticated Key Exchange?

I am reading some articles about Key Exchange. I know classic key exchange,such as Diffie-Hellman key Exchange. This type algorithm is vulnerable to man-in-the-middle attack. However, When using ...
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### Recovering password from zip file [migrated]

I have a few zip files from a long time ago but they are encrypted and I don't know the passwords. I have the unencrypted, uncompressed file that is in one of them. With this pair, I am trying to ...
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### Converting a message from one PGP key to another PGP key

I have a message $M$ that is encrypted using a public key $P_1$. I lost the associated private key $p_1$. I have another public/private key pair $(P_2, p_2)$. Is it possible to "translate" the ...
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### RSA low exponent with padded plain-text

Considering a case, when modulus is large and hard to factor, exponent e=3 and there is a cipher-text which is created by padding plain-text with ...
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### Is openssl rand command cryptographically secure?

I'm wondering if the openssl rand command produces cryptographically secure random bytes. For example when in need for a random password or token: ...
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### RSA find public exponent

Suppose I have an encryption oracle which can encrypt $m^e \mod n$ for any $m$. I know $n$ and I know $\varphi(n)$. However the public exponent $e$ is secret. Is it possible to figure out it's value ...
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### Why doesn't “Classic McEliece” need scrambling?

The original McEliece scheme uses two random matrices S and P to scramble the generator matrix and uses $\mathsf S·\mathsf G·\mathsf P$ as the public key. The Niederreiter variant also does about the ...
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### Which functions can be used as Pseudo Random functions? Can block Ciphers be used for this purpose with our own encryption function?

Since the cloud security algorithm I am trying to implement says that for a PRF, any secure encryption algorithm or a keyed hash function can be used. The security parameter I have chosen is 15 bits ...
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### Need help deciphering this ciphertext which I don't know its algorithm [on hold]

I got a base 32 code which I decrypted to get another ciper but don't know how to decrypt. base32 code: ...
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### What is the difference between discrete-then-gaussian and gaussian-then-discrete?

In lattice cryptography, we always face the probem of discrete gaussian sampling. To the beginners, it is a bit complex. However, gaussian sampling from a continous space is much easier to understand, ...
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### Protocol Design for IoT devices having PSK using AES-GCM

Handshake: 1) Client To Server: "AES-GCM(Client_random_128bit,client_iv,psk),client_id,tag,client_iv" 2) Server To Client: "AES-GCM(Server_random_128bit,client_iv++,psk),tag ...
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### Is OpenSSL HMAC vulnerable to length extesion attacks when using MD5 as hash algorithm?

Given that a valid hash for a specific payload is known, would some C code like this be vulnerable to a length extension attack? ...