# All Questions

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### Is RSA-OAEP secure when e=3? [duplicate]

Is RSA-OAEP secure when the exponent is equal to 3?
30 views

### Resynchronizing brute-force attack against stream ciphers

There is a stream cipher without any known cryptographic weaknesses. The attacker knows parts of the key so she can reduce the key-space to a size that can be practically brute-forced. However the ...
83 views

### Why not send the identity in the encrypted message?

I've recently started reading the book "Applied Cryptography" written by Bruce Schneier. Quite a few times I stumbled across protocols who send the identity outside of the encrypted message (see step ...
115 views

### Differential Fault Analysis of AES

Let's say: an error is induced into an implementation of the AES-128 to produce a faulty ciphertext. The error is a one-byte eror and is always induced on the last state byte, during round9, before ...
51 views

### Implementing modular reductions (n*n) [closed]

I'm implementing a public key cryptosystem in a proprietary System On Chip that only allows modular reductions by $n$. However, that cryptosystem requires ($n^2$) modular reductions. Perhaps someone ...
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### Can CKM_RSA_PKCS signature be made secure by lowering its maximum input size?

The CKM_RSA_PKCS Mechanism in PKCS#11 v2.20 section 12.1.6 PKCS #1 v1.5 RSA is a signature scheme commonly used to implement RSASSA-PKCS1-v1_5 of PKCS#1 signature of data hashed externally to a ...
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### Signature constructor using Self-signed certificate

I've the following scenario: One application signs JWT access/id tokens using the private key contained in a self-signed certificate, and then passes its public key to other parties to validate that ...
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### Given only RSA public key parameters, what security issues might I be able to detect?

I'm attempting to automate some checks against a large list of .NET assemblies, and want to include a test to see if the RSA parameters used to sign the assemblies are sensible. However, since I don't ...
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### CCA-attack is possible in RSA, but how the decryption key $d$ is known to anyone

CCA-attack is possible in text-book RSA, but how the decryption key $d$ is known to anyone, as it is kept secret with receiver.
48 views

### Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is this What I really need is basic explanation of the ...
65 views

### Steganography Decryption From Completely Black Image

I am trying to decrypt a completely black gif that I know has been encrypted by some sort of steganography. I've tried subtracting the bytes of the images with each other, and so far I have gotten a ...
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### Where I can find a list of certified software / hardware RNGs compliant to NIST SP 800-22?

I need to use NIST SP 800-22 approved software / hardware to generate RSA key pair. Where I can find a list of certified software / hardware RNGs compliant to NIST SP 800-22? And how is the SP ...
110 views

### Factoring two RSA modulus with known $|p_1 - p_2| < \ell$

I have two 1024bit RSA modulus $N_1 = p_1q_1$ and $N_2 = p_2q_2$ such that $0 <|p_1 - p_2| < \ell$, and $\ell$ is at most 64bit integer. Can I factorise $N_1$ and $N_2$? What's the answer when ...
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### why do files downloaded with http and https have the same size?

while working with Encryption mostly cipher text is always larger the plain text, why isn't that the case when downloading a file using https ? even that compression isn't much used anymore because if ...
17 views

### Block size of 128 bit in (quantum) future [duplicate]

Is a block size of 128 bit enough to ward off expected attacks in the future (something like 30 years ahead) with the possible risk of quantum computers? Other formulation: If we were to create a ...
33 views

### Requested to encrypt data with AES256, digital certification, timestamped

at my job we have been tasked by gov to encrypt some data we send to them. The "law" says we have to do the title above, but they only need us to do the AES256 thing because the data is not really ...
26 views

### How to check if a sequence is generated by a linear congruential generator? [duplicate]

Assume a linear congruential generator is defined by $x_i=(x_{i-1}\cdot a+c)\bmod m$ and I am given the values $a$, $c$, $m$ and a sequence of numbers starting at the $n$th bit. Can I tell whether ...
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### decrypt a saml 2.0 response having aes 128 and rsa [closed]

I need to decrypt a saml 2.0 response. But, the response object has reference to aes 128 and rsa algorithms, and I am having hard time in finding a way to decrypt. Below is the structure of the ...
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### RSA Decryption from samples

I am working on a project for a client which involves decryption of data which was encrypted using RSA. The system in question retains three independent copies of each data-set, but each copy is ...
105 views

### Why does consecutive permutations or consecutive substitutions not enhance security?

My professor stated that permutations which are done repeatedly does not further enhance security than just one permutation. He also stated that fact this applies to consecutive substitutions as well. ...
122 views

### RSA key pair generation and FIPS 140-2, 186-4

I need to securely generate RSA key pair and I need to have access to private exponent in order to process it further. What's the difference in FIPS 140-2 and FIPS 186-4 in connection with RSA key ...
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### Does “cryptography rather [try] to minimize the expansion of ciphertext”?

In a question's comment on crypto.SE (Is there an efficient way to hide the encrypted plaintext length with a block cipher?) it was stated cryptography rather tries to minimize the expansion of ...
47 views

### Statistical saturation attack on block ciphers

I was wondering if anyone around here could give me some explanation on this type of attacks. Pretty much the only thing that I could find is this What I really need is basic explanation of the ...
83 views

I'm pretty new to this and find it quite interesting, but my brain won't process how it works so I have to ask some questions :) Why is cryptography used? Is it for extra security once the password ...
25 views

### What is the benefit of applying the tweak a second time using XTS?

I tried to understand the inner working of XTS. What I understood is that it is applying the tweak two times: once on the plaintext and once on the output. What is the benefit of applying the tweak ...
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### Is there any task better and less complex than oblivious transfer? [closed]

I wanna know whether there can be any algorithm less complex than oblivious transfer because OT consumes O(n) time complexity where n is the number of messages involved. So can you please help me out ...
90 views

### Java RSA Padding: no libraries used

I'm trying to implement RSA without using any java libraries using the algorithm from wikipedia HERE So, anyone can clearly see that it is a raw RSA, and can directly be attacked. The question is ...
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### What does variable-base point/scalar multiplication mean in ECC?

I am a bit confuse about the term, variable-base point/scalar multiplication, in Elliptic Curve Cryptography. What I have understood so far. It means that the base or point on EC is variable/unknown. ...
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### Encryption with a known plaintext

I'm building an application where users can be a part of groups, and can obtain and distribute URLs from the group page that allow anyone who clicks on them to join said group. Groups should not ...
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### How do you break encryption on a message? [closed]

This may seem like a simple question, but I have just started studying cryptography and I can't seem to find any information on this at all. I am trying to write a "simple" encrypted messenger using ...
320 views

### AES encryption takes more time to decrypt than encrypt

I am trying to find how much time an AES encryption and decryption takes for a given amount of data and key. In all the cases encryption takes way lesser processing time than decryption. I tried to ...
4k views

### Avalanche effect in DES

I couldn't understand the avalanche effect in DES. Could someone explain how avalanche effect happens in DES
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### Weakness in double hashing? [duplicate]

I remember reading an account of how double hashing (i.e. sha256(sha256(x))) can make some form of communication protocol between Alice and Bob trivially insecure, ...
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### Key Length vs KeySpace

I am a newbie here, this is my first post. I have searched the forum but I haven't found a clear answer to this. In general. What is the relationship between key length and the keyspace? (if there ...
54 views

### Key exchange using hash function

Consider two types of attackers on a key exchange (KE) protocol and subsequent communication between the parties which used this KE instance to establish a secure communication key. Attacker Eve ...
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### Why are twofish or other algorithms not NIST approved, are they still safe?

NIST has a total of 3 approved block ciphers on their website: AES, TDES and skipjack. I get why those are on there (though personally I find TDES a bit iffy) but from my understanding Twofish and ...
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### If the text was compressed before using traditional cryptography, how much difficulty increases for frequency analysis attack?

Traditional encryption is weak and no longer be used. They can be easily broken by using frequency analysis is a well-known fact. But, the frequency analysis often depends on the number of captured ...
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### Beginner question about secure communication with one user using DES

I am currently learning about encryption and I was asked a question: If a user wants to securely communicate with another user but only uses a DES crypto system. With no shared DES key with the other ...
52 views

### Block cipher mode with diffusion on ciphertext

As I understand, diffusion property in AES-CBC ensures that one-bit change in plaintext will yield changes in all following blocks in ciphertext upon encryption. I'm looking for algorithm that will ...
102 views

### Why is this a fix to Bleichenbacher's attack?

Looking at the excellent explaination of the attack here: Can you explain Bleichenbacher's CCA attack on PKCS#1 v1.5? I have one additional question: It says that: ""To prevent this attack, SSL ...
192 views

### Timelock puzzle improvment

I came across this question with this answer about a cryptographic timelock-puzzle that needs approximately 30 years to be solved. There is also an explanation with source code for that puzzle ...
87 views

### The Inhomogeneous Short Integer Solution (ISIS) problem with a clue

The Inhomogeneous Short Integer Solution (ISIS) problem is as follows: given an integer $q$, a matrix $A \in \mathbb Z^{n\times m}_q$, a vector $b\in \mathbb Z^n_q$, and a real $\beta$, find an ...
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### WPA and WPS: connection method [closed]

Do clients use WPS every time when they connect to a WPS-enabled AP? Or maybe they do it just the first time and then they switch to a normal WPA/WPA2 key exchange? If the latter, it's possible for ...
83 views

### Self verifying hash algorithm

For quite some time I've been thinking about the idea to construct a hashing algorithm that contains its own checksum value, and thereby can verify itself. With hashing algorithms like SHA1 and MD5 ...
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### Generic name for (?hash) functions of form $\{0,1\}^n \rightarrow \{0,1\}^{poly(n)}$

Consider a function $$f: \{0,1\}^n \rightarrow \{0,1\}^{poly(n)}$$ with the following properties: hard to invert, i.e. given $f(x)$, hard to find $x$ hard to find a collision, i.e given $f(x)$, ...
67 views

### Inconsistent terminology for ciphers and algorithms

I've been baffled by all the different kinds of names which are given to cryptographic algorithms. There are block ciphers and stream ciphers (AES and RC4). There is symmetric and asymmetric ...
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### Attack on key exchange with authentication

Suppose the honest parties - Alice and Bob - exchange public key in person/via telephone so that attacker can only eavedrop on the line. Alice has hashed the public key using a collision resistance ...
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### Security of integrity protection with HMAC vs AEAD

I'd like to know how the security of the integrity protection compares between: HMAC-SHA-256 with an 32 byte tag or a truncated 16 byte tag AES-GCM with a 16 byte tag AES-CCM with a 16 byte tag or ...