0
votes
1answer
80 views

Where have all the cypherpunks gone?

In 1992, cypherpunks was created as a mailing list for activists advocating for cryptography. Arguably, the cypherpunks mailing list was the foundation for the movement and the centre of it all. ...
0
votes
1answer
40 views

Simple encoding function mapping integers [on hold]

I am trying to analyse the following function. From an integer inputs it generates a series of 5 numbers. When looking at the some valid samples, clearly I can recognize some patterns (42 is ...
0
votes
2answers
96 views

DHE key exchange. Is it really secure?

Context I recently came across a video on the net showing the process of key exchange in Diffie Hellmann. Alice and Bob want to communicate. Eve is the (wo)man in the middle. This video is the ...
0
votes
0answers
23 views

Should I use a key store to keep my symmetric keys

I'm maintaining an application which handles several keys to encrypt/decrypt information. Some keys are used to encrypt text (user passwords, some sensitive data in the db, etc). Some other keys are ...
0
votes
1answer
45 views

Java: How to handle authenticated encryption for big files

First I need to mention that I can't use BouncyCastle to implement this solution. I have to encrypt files into the file system. Those files are not going to be tranfered over the wire to any other ...
1
vote
2answers
86 views

Encryption of big files in Java with AES/GCM

I have to encrypt big files. Say their size ranges from 500mb to several of gigabytes. I would like to use AES/GCM/NoPadding as provided by Java 1.8 since that gives me automatic authentication and ...
0
votes
0answers
19 views

if using cbc+hmac dealing with small size of data(less than 128bit) , will it cause any problem?

if use AES-cbc,HMAC-SHA256, and there is some txt needed to be enc, and I divide this txt into small packages with variable length, then enc them. some of these package can be less than 128bit. Is ...
0
votes
1answer
37 views

What happens when cbc+hmac get a replay attack?

If it use AES-CBC and HMAC-SHA256 for message send online, and someone try to replay attack on this message. Can the attack be successful? what will be happen when attacking?
1
vote
1answer
37 views

Is the output of AES-CBC + MAC the same size as the input?

I use AES-CBC and HMAC-SHA256 to encrypt a text file. Will the output be larger in size than the input or will it be the same size? Is it more secure secure if the size of the output is larger?
2
votes
1answer
40 views

Do data-dependent rotations have any advantage over fixed rotations?

There are many ARX ciphers, however most use fixed rotations. I know data-dependent compared to fixed rotations are: patented harder to implement constant time more expensive in hardware harder to ...
2
votes
2answers
161 views

Is there a way to systematically calculate the public exponent $e$ in RSA?

I'm learning RSA in one of my classes and we were given a problem: $p = 5$, $q = 11$ I have done the following steps: $n = 5 \cdot 11 = 55$ $\phi = (5-1)\cdot(11-1) = 40$ I know that to ...
0
votes
0answers
29 views

Elliptic curve trapdoor function without modular arithmetic?

From what I understand, an elliptic contains a set points satisfying the equation $y^2=x^3 + ax + b$ together with the point at infity. It seems clear how multiplication with a scalar and a point ...
0
votes
0answers
33 views

How many characters per block in an El Gamal ECC cryptosystem?

While I look for how many characters that can be encrypted using the The elliptic curve ElGamal cryptosystem. of each block found for these lines. But I can not understand Actually in our case we ...
-1
votes
0answers
42 views

Which Encryption Method is used for this stream cipher? [on hold]

Plaintext: 378734493671000 Encrypted: +VZyZlAHP6HAgoaPBrBz +VZ is common on all data there, so encrypted data might be yZlAHP6HAgoaPBrBz I think this is stream cipher? Could anyone tell me which ...
0
votes
0answers
27 views

Find the encryption method from the cipher and plaintext [closed]

I have been given iogdaybDfD which is a cipher of the word narcolepsy. I need to find the type of encryption that has been applied to narcolepsy to encrypt it to iogdaybDfD. Could anyone advise on how ...
0
votes
0answers
18 views

CP-ABE: structure of the secret key SK

I am working on Ciphertext-Policy Attribute based Encryption (CP-ABE) and I need to understand how a secret key looks like. For example, assume that the universe of attributes is defined to be ...
0
votes
0answers
40 views

Interactive assumptions not falsifiable?

Can someone explain why an interactive assumption is not falsifiable? Maybe I'm misunderstanding what the statement means, but isn't even a non-interactive assumption interactive, but just with a zero ...
0
votes
0answers
24 views

Java RSA/ECB/PKCS1Padding encryption with .NET [closed]

I need to encrypt a password on a web site developped in .NET using a public key. The public key is delivered through a Java web service with the information: The key is a RSA key to be used with ...
5
votes
0answers
67 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 ...
-1
votes
1answer
56 views

Full Disk Encryption Alternative [on hold]

Since developers of TrueCrypt discontinued their software, i'm looking for a alternative. It should be pre-OS, so that just after Bios, the Password is requested. Like in TrueCrypt. I took a look ...
-2
votes
0answers
60 views

Crypto Challenge.sucked [closed]

The solution was hardened using MD5(MD2(SHA1([a-zA-Z]{6}))). Now crack this: e24b02c81cabe0d4af45f9ceaccde2c7 i couldnt crack it.
0
votes
1answer
53 views

special public keys and modulo n

I just picked up cryptography and have some questions on RSA cryptosystem: Say there are two public keys (n, e1), (n, e2), e1 is coprime to e2. They share the same n. Is it possible to find the ...
1
vote
0answers
69 views

How can I start the following crypto project?

(Cryptography: encrypting files before storage in the cloud): The project consists of a software implementation of a method to pre-process a file before storing it on a cloud storage server so that ...
0
votes
0answers
30 views

proving the security of 1 out of 2 oblivious transfer using AND function

Hello ladies & gentlemen, I need to improve the security of 1-out of 2 oblivious transfer using AND function method with a given info. use one-out-of-two oblivious transfer as building block, ...
0
votes
2answers
36 views

Bouncy jdk 1.51 Serpent KAT tests vs Nessie vectors

Having a little trouble getting Nessie vectors working with the Bouncy Castle SerpentEngine. Do the Nessie vectors require a mode or some pre-processing? Nessie Serpent 128, set 1, vector 0 reads: ...
0
votes
0answers
24 views

number theory and cryptographic hardness assumptions [on hold]

Let p be a prime and e>=1 an integer. Show that the totient(p^e)=p^(e-1)*(p-1). Let p,q be relatively prime. Show that the totient(pq)=totient(p)*totient(q). (Dont use chinese remainder).
0
votes
1answer
49 views

what does rsaSha512Sign do?

I have the following function: ...
0
votes
0answers
48 views

Key generation in Digital Signature Algorithm

In DSA, one needs to generate two primes $p$ and $q$ such that $q$ is $256$-bit and $p$ is $3072$-bit and $p-1$ is a multiple of $q$. Question: How to generate such $p$ and $q$. Attempt: First, use ...
1
vote
1answer
63 views

Many single-time use keys encryption scheme (not Shamir's Shared Secret)

I'm looking for encryption scheme with the following properties: There's a sequence of keys that can be used to decrypt the message Strictly only one key from the sequence is required to decrypt the ...
0
votes
1answer
79 views

Collision resistant hash functions

Let (Gen1,H1) and (Gen2,H2) be two hash functions. Define (Gen,H) so that Gen runs Gen1 and Gen2 to obtain keys s1 and s2, respectively. Then define Hs1,s2(x)=Hs1(x)||Hs2(x). a) Prove that if at ...
0
votes
1answer
40 views

Show CBC-MAC construction isn't secure [closed]

Show that the basic CBC-MAC construction is not secure when used to authenticate messages of different lengths.
0
votes
1answer
36 views

Rabin Cryptosystem Problem (variant)

My understanding of Rabin We have p and q which are distinct primes congruent to 3 mod 4. ...
0
votes
1answer
87 views
+50

Secure Multiparty Sum in malicious model using threshold encryption

Suppose $n$ actors each hold a plaintext $p_i$. We wish to find $\sum p_i$, without leaking any information about individual $p_i$. Any actor (or any link in the network) could be controlled by an ...
0
votes
1answer
72 views

BruteForcer XOR (bfxor.exe) to attack 64-bit keys and longer

First of all, this is not a beginner's question since I already know a good deal about encryption and brute-force attacks. This is also no question on how to code programs for brute-force attacks ...
0
votes
0answers
53 views
0
votes
1answer
35 views

OpenSSL RSA same plaintext but different ciphertext

how OpenSSL RSA work ? I generate public (n,e) and private key (n,d) then I encypted a file by : ...
0
votes
1answer
31 views

plaintext distribution ,perfect secrecy cryptosystem

I have been trying to solve the next problem: let pi be a perfect secrecy cryptosystem with specific plaintext probability distribution. How to prove pi will have perfect secrecy for all other ...
0
votes
1answer
56 views

fully homomorphic encryption (FHE)

Please, I would like to find some hints or solution to my following problem, I would appreciate your assistance to walk with me throughout the solution Given fully homomorphic encryption (FHE) ...
0
votes
1answer
42 views

Why sorting is needed for Meet-in-the-middle attack

The weakness of double DES, E (k1, E(k2, M)) is that Meet-in-the-middle attack is possible. When performing Meet-in-the-middle ...
0
votes
0answers
30 views

Importance of ShiftRows in AES

If ShiftRows is excluded from AES, then an attacker can attack the modified AES by simply treating $128$-bit input as $4$ $32$-bits blocks. The attacker can attack these $4$ blocks separately. ...
1
vote
1answer
19 views

extract ciphertext from encrypted SMIME file

the main question of this message is how to get the true ciphertext from S/MIME file? I created RSA keys and encrypted a message with S/MIME as follow : ...
0
votes
0answers
26 views

Secure symmetric encryption algorithm for any-size base62 data

I am searching for a secure algorithm to encrypt base62 (or any other base) data for ids in urls. It should feature: No blocksize etc, limiting the length of the message to a factor of n If you ...
1
vote
1answer
52 views

Block cipher to encrypt 8 bytes/64 bits - Use 64 or 128 bit cipher?

Here's the problem: I have a transport stream that I have been requested to encrypt between the transmitter and receiver. The data size is at most 8 bytes so it seems I can only use ECB as I only have ...
2
votes
2answers
49 views

Checking both Quadratic residuosity and Jacobi symbol simultaneously and efficiently

I have to randomly generate a number $u$ such that $u \in J(N)-Q(N)$ where $J(N)$ denotes the set of elements less than $N$, whose Jacobi symbol value is equal to 1; and $Q(N)$ denotes the set of ...
5
votes
0answers
52 views

Why is Poly1305 popular given its 'sudden death' properties?

ECDSA has the undesirable property that if a key pair reuses a nonce in a signing operation, the cryptosystem experiences catastrophic failure in the form of private key leakage. I've heard this ...
0
votes
1answer
63 views

Decrypting A Cipher Text without knowing the key or plaintext

i'm new to cryptography and i am doing a research based on cryptanalysis of vigenere cipher. If i have a ciphertext which is encrypted using vigenere cipher, is it possible for me to decrypt the ...
0
votes
0answers
50 views

How does chosen ciphertext attack on Elgamal work?

Can it be proven that attacker can obtain the full message if he knows some plain-ciphertext pairs?
0
votes
0answers
60 views

Complexity to find an preimage of a hash function

Suppose a hash function based on Merkle-Damguard construction. Its compression function is given as $H_i=E_{m_i}(H_{i-1})$, where $E_{m_i}()$ denotes the encryption of an ideal block cipher with ...
1
vote
2answers
336 views

Why we can't implement AES 512 key size?

Out of curiosity why we can't implement AES 512 key size? Please explain somehow i can understand! I'm not an expert.
1
vote
1answer
40 views

Key derivation for AES-Encryption key and HMAC

Okay so I have two options for how I would derive two keys for AES encryption and HMAC they are as follows: Run BCrypt on a users passphrase and then use the bouncy castle implementation of HKDF in ...

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