0
votes
0answers
90 views

public/private key: is it possible to have master public/private key

This may be a very primitive question which might not be possible but I have this question to understand. Assume Yahoo provides a messenger where yahoo users can chat in secure way (end-end ...
1
vote
3answers
140 views

Adding dummy bytes to ciphertext

I was wondering if interleaving the resulting crypted data with dummy bytes placed at random positions but known in advance by the peers could improve security (no matter the algorithm and strength ...
2
votes
0answers
50 views

can pairings only be used with elliptic curves?

As far as I understand one big advantage of ECC is that we can use pairings on the group of torsion points of the curve. I was wondering if it is possible to construct pairings from general finite ...
2
votes
0answers
78 views

Scale-Invariant DGHV Scheme - Decryption

I have just started reading the Scale-Invariant Fully Homomorphic Encryption over the Integers paper and I'm a bit confused about something: When decrypting the ciphertext: $c = r + (m+2r^*) \cdot \...
3
votes
1answer
181 views

How to clock a linear feedback shift register?

I have some trouble understanding what happens when a LFSR is clocked. I have tried many examples but I do not get the correct result. Can anyone point out my errors? I have the following polynomial: ...
0
votes
2answers
54 views

How hard to solve the given mod problem

Let c = a.b mod p where p is n bit prime number (e.g. 128 or 160 bit prime number); a - random number between 1 and (p-1); b - random number between 1 and (p-1); Given c, a and p, how hard to ...
1
vote
1answer
46 views

Is there a standard prefix random padding scheme?

Is there a standardized padding scheme which is prefix instead of postfix and that uses random bytes except for the first byte which would be the length of the padding?
3
votes
1answer
105 views

Is there any benefit of changing the AES-CCM encryption key periodically even if the Nonce space is not exhausted yet?

I would like an answer that could be sustained by a mathematical proof. Let's say I'm using AES-CCM to encrypt a lot of messages, and I always use a different nonce. I know that when the nonce space ...
4
votes
1answer
73 views

Should the signature be prefix or postfix to the message in the sign-then-encrypt scheme?

Let's assume we have a message $M$ and it's signature $S$ and that $|$ is the concatenation operator. Should we encrypt $S|M$ or $M|S$? Does it even matter?
0
votes
1answer
68 views

How can I turn this cipher into a perfect cipher by altering only its encryption algorithm?

Given a toy cipher that picks a key, k, from the key space of {00,01,10} and a message,m, from the same set {00,01,10} and encrypts using E = m ⊕ k. How can I change the encryption function E in ...
2
votes
1answer
444 views

What is required to decrypt an encrypted file?

At the risk of sounding stupid and being laughed at...I must ask this question. What is required to decrypt an encrypted file? Obviously you need the appropriate key to decrypt, but is any other ...
0
votes
2answers
90 views

The benefit of PBKDF2 for big keyfile?

The man page of cryptsetup says: Whenever a passphrase is added to a LUKS header (luksAddKey, luksFormat), the user may specify how much the time the passphrase processing should consume. The ...
2
votes
1answer
255 views

Given a linear block-cipher,how can an attacker decrypt any plaintext value encrypted,using 128 chosen ciphertexts

Given the linear block cipher $\operatorname{LinearCipher}(k, p) = c$ $$\operatorname{LinearCipher}(k, p_1 \oplus p_2) = \operatorname{LinearCipher}(k, p_1) \oplus \operatorname{LinearCipher}(k, p_2)$...
2
votes
0answers
26 views

Raw /dev/random output for keymat [duplicate]

Noob question: It is my understanding that the raw output from non-blocking /dev/random (where the kernel's entropy_avail estimate is equal to or greater than the number of random bits required) ...
2
votes
1answer
144 views

Very short signatures? (eg: 48bits?)

Our application requires some 'mild' form of 'proof of origin' for the tokens we issue (~200 bytes), however, the value of each is trivial. The requirement is to provide 'tamper resistance' rather ...
3
votes
1answer
302 views

ECDH or RSA more secure for symmetric key wrapping?

Suppose a message is encrypted with a symmetric block cipher with a random key. RSA is often used to wrap the symmetric key using the recipient's public key. In this case, the size of the message is ...
1
vote
3answers
63 views

Does a padding oracle have the encryption key? Where in real life do I see such an oracle?

So after some searching, I kinda know the attack procedure of altering bit by bit. But I'm still confused how this is possible. If I understand it correctly, the attacker never has the key, or tries ...
0
votes
1answer
21 views

Why many passes at file removal? [closed]

Why file removal tools offer gost 2 passes and British 3 passes or even gutman 35 passes options? In which case the single pseudo random pass is not enough?
2
votes
0answers
56 views

Using a product of a series of curve25519 scalars as a private key

There are a few systems like the GNU Name System and the Sphinx mixnet packet format that employ a series of curve25519 scalars all multiplied together as a private key. Are there any caveats to ...
3
votes
3answers
853 views

For any hash value, is there an infinite number of inputs that hash to it?

Bruce Schneier writes (back in 2005) in a post on cryptanalysis of SHA-1: SHA-1 produces a 160-bit hash. That is, every message hashes down to a 160-bit number. Given that there are an ...
2
votes
1answer
311 views

Testing hash functions for collision resistance

I was hoping to implement a software that allows testing a user-defined hash function for cryptographic properties (Meant to pique interest in cryptographic hash function for a school showcase), as ...
1
vote
2answers
177 views

MD5 Collision Attack Explained

In one of my assignments, I came across this line Due to MD5’s length-extension behavior, we can append any suffix to both messages and know that the longer messages will also collide. This lets ...
6
votes
1answer
113 views

Encoding scalar values to points on Ed25519

I'm interested exploring key derivation and threshold signature protocol that require point arithmetic (addition) on the private scalar values and $S$ values of the signatures in ed25519. ...
4
votes
2answers
115 views

Weakness of SRP after server compromise

From SRP section 3: The host stores user passwords as triplets of the form { <username>, <password verifier>, <salt> } Password entries ...
2
votes
1answer
62 views

Weaknesses of RFC6628

In RFC6628 section 2.2, they say: w = The password remembered by the user. W = The password verifier registered in the ...
-1
votes
1answer
100 views

About end to end algorithm SMS from Jo Mehmet Sollihagen Øztarman [closed]

This is a signcryption scheme from End-to-End Data Protection of SMS Messages by Jo Mehmet Sollihagen Øztarman (pdf, section 4.3.1): Public parameters C: an elliptic curve over GF(ph) with p ≥ 2^...
6
votes
1answer
284 views

Is it possible to find a Mersenne Twister seed given only the first output?

Suppose I have a Mersenne Twister seeded with some unknown value, and I’ve been given the first output. Given only this first output, and no other information, is it possible to derive the unknown ...
3
votes
1answer
125 views

Can homomorphic decryption of DES be practical?

I was reading this paper Homomorphic evaluation of the AES Circuit by Gentry et al. when I thought if something similar can be done with DES or 3DES, e.g. it is plausible to decrypt DES ...
4
votes
1answer
108 views

Effect of message length on collision attacks

I know that message collisions are supposed to be hard to calculate for a good cryptographic hash. Given 1k worth of data, it's hard to find another 1k worth of data that collides with the same hash. ...
4
votes
1answer
77 views

What is the complexity of finding SHA-1 collisions?

Given the recent news about SHA-1 collisions, what is the complexity of finding a SHA-1 collision? Marc Steven's HashClash is still detailing about 260. Does the previous complexity still hold?
3
votes
1answer
77 views

Are HTTPS web sessions non-repudiable?

(This is probably a basic question, and may be a duplicate; if so, just let me know.) Suppose there are two clients A and B, ...
4
votes
3answers
477 views

Can an ephemeral RSA key give forward secrecy?

Suppose party A generates an ephemeral RSA key and sends the public key to B. Party B then generates a symmetric key, encrypts it with Party A's public key and sends the Ciphertext to Party A. Party ...
3
votes
1answer
152 views

Avalanche effect sample size

With a fixed key size – key has 128 bits, while block size is 8 byte – how do I calculate how many different keys and texts I have to test for an cryptanalytic statistics study? Differently worded: ...
3
votes
1answer
103 views

Are there full cycle cryptographic/one-way hash primitives?

I'm looking for behavior similiar to that of LCGs, (i.e. input and output sizes are same). Full cycle of $2^{32}$ different inputs generates full cycle of $2^{32}$ different outputs, distribution of ...
2
votes
1answer
72 views

Inverting One-Way Functions

One of the conditions that a one-way function has to satisfy is the following: $$Pr[A(f(x))\in f^{-1}(f(x))] \leq negl(n)$$ Now, suppose that we have the following function that's not one way: $$f(x)...
1
vote
1answer
77 views

Encrypt hash using hash of hash?

I wonder what is wrong with this scheme for authentication. Server sends random challenge, C Client returns (C, B(P)) encrypted in H(B(P)) where B(P) is high work factor salted hash of the user ...
2
votes
1answer
68 views

What is the notion of an interactive assumption?

In this paper: Sequential Aggregate Signatures with Short Public Keys: Design, Analysis and Implementation Studies the authors sell the paper as the first who propose Aggregate signatures without ...
0
votes
1answer
69 views

PKCS5 having no padding

I am using the javax.crypto.Cipher in Java to do AES/CBC/PKCS5Padding encryption. What I am observing is that, if you try to encrypt a Plaintext with no padding, PKCS5 adds another entire block just ...
7
votes
3answers
352 views

How to protect key in software

I need to encrypt/decrypt data from my software by AES, the problem is how to make the AES key secure, there is no HSM, should I hard code the key in my code? It seems that a hacker can read the key ...
2
votes
1answer
78 views

Secret only known on consensus

Does a method exist where a secret is generated so that is is unknown until 3 or more people (predetermined) reach consensus that it should be revealed?
4
votes
1answer
72 views

Is there a cryptographic protocol that let's me prove someone has a large binary?

I'm working on a system that has a P2P component. When an individual downloads a binary and decides to mirror it, they advertise themselves in a providers set. The binaries can range from 1-1000MB. I ...
2
votes
2answers
115 views

Inverting RSA function

I am in high school and I am writing a paper on RSA. I want to show that low values of the public key exponent can make it easy to 'invert' the function so that the encrypted message can be recovered. ...
2
votes
0answers
50 views

Construct points with the same discrete logarithm

Assume we have an elliptic curve $E$ with a Tate (or Ate,...) pairing $G_1 \times G_2 \mapsto G_T$ Now the task is to find $g_1, g_1' \in G_1$ and $g_2, g_2' \in G_2$ such that the discrete logarithm $...
2
votes
2answers
117 views

How does perfect hash function works?

According to wikipedia, a perfect hash function is a hash function that uses algorithms that has a certain random aspect to their logic. It is suppose to be collision-free. However due to the pigeon ...
1
vote
1answer
77 views

The example of Wikipedia on steganography doesn't work

I was reading some stuff on steganography. There is an example on the wikipedia page : However, I tried many software to get the hidden image, but no one worked. Is there anything wrong about that?...
4
votes
1answer
83 views

Creating own ciphertext after a padding oracle attack?

I've written a script that breaks a cipher text based on a padding oracle for an assignment, but was wondering how I would continue on to create my own cipher text with any plain text I desired? ...
2
votes
3answers
206 views

Hypothetical encryption technique, is it secure?

This to me, sounds like a great idea, but with all rosy-tinted ideas it needs some grounding in reality. Here are the steps of the hypothetical system (with the hypothetical part highlighted): User ...
1
vote
2answers
128 views

Is it worth hiding an AES encrypted text string in a PNG image for better security?

I need advice as to whether it is worth the extra "security" and processing of an AES encrypted text string to be hidden in a PNG image as opposed to an AES encrypted text string to be saved in a read-...
3
votes
1answer
45 views

X509 certificates: Two Algorithm Identifiers?

I'm wondering why there are two Algorithm Identifiers in a X509 certificate. One is in the "to be signed" part and the other one is at the end right before the actual signature. Are they used for the ...
41
votes
1answer
4k views

What is a “freestart collision”?

In their work on SHA-1 collisions (cf. the EUROCRYPT-2016 paper “Freestart collision on full SHA-1” by Stevens, Karpman, and Peyrin) Stevens et al show that they are able to generate "freestart ...

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