0
votes
3answers
66 views

How does the certificate trust model work in detail?

How does the whole achitecture between the certificate authority (e.g VeriSign) and its clients (e.g foo.com) work. How does my browser know that foo.com hasn't created its own certificate, wrote ...
0
votes
1answer
55 views

What Does This Symbol Mean? (Hardcore Predicates for One-Way Functions)

I am studying Pseudorandom Number Generators and when reading the discussion on One-Way Functions and Hardcore Predicates, I came upon this equation. $$b(x,r)=\displaystyle \bigoplus_jx_jr_j$$ I ...
0
votes
1answer
53 views

How does a user register his verifier at host in SRP (Secure Remote Password) protocol?

I read RFC 2945 and 5054 describing SRP, but there was no mention of registration. How should user registration happen in SRP? Is there a standard or paper describing it?
0
votes
1answer
57 views

Miller Rabin - Error probability of .5 a possibility?

I'm testing the property of Miller Rabin that the error probability is at most 1/4 when only a single base a is chosen and we iterate only one time. We are testing odd integers 90,000 to 100,000. ...
0
votes
1answer
69 views

If PRF is non invertible, why does Ctr-mode work?

I am currently taking Dan Boneh's Cryptography I course online. I have just finished the segment discussing the Cipher Block Chaining and Counter-Mode. I am having difficulty understanding why ...
0
votes
1answer
121 views

Is it possible to correct the exponent of an RSA public key if it has been altered?

Is it possible to change the exponent of an RSA public key?
0
votes
2answers
73 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 ...
0
votes
1answer
237 views

Computing the padding of MD5

So I'm reading this question to learn more about length extension attack, and I want to make sure I understand the basics of padding. It says in the post that given the hash and the length of the ...
0
votes
1answer
55 views

How can I prove I have a certain Facebook account by signature?

I would like to know how to prove I have certain Facebook account (or that I can login to that account).
0
votes
1answer
55 views

Is it safe to use MD5 in a proof of work system?

Here is the POW system: you are given a string and you need to compute a suffix so that first few bits of the MD5 value are all 0. I know MD5 is collision vulnerable, but is it safe to use MD5 here, ...
0
votes
2answers
46 views

Certificate Path Verification of X509 Certificate

I have the trusted root certificate which I am validating using the self signed key. I also have the intermediate certificate, which i am validating using the root certificate. Now when i am ...
0
votes
2answers
115 views

Determine if a public key point y is negative or positive, odd or even?

Take an elliptic curve cryptography public key (x, y) and its additive inverse (x, -y). How do you identify which is the positive point and which is the negative point? Examples: Private key 1 -> ...
0
votes
1answer
45 views

How to deliver an encrypted message to multiple recipients without revealing keys

Let's say I have generated a private and a public key. I create a message and encrypt it with the public key. I deliver this encrypted message and a private key to multiple recipients. Why would I do ...
0
votes
1answer
347 views

How long does it take to brute force a Wordpress password?

I'm not a cryptograhpy expert, I am a web developer trying to determine the origin of a Wordpress blog hack, and how likely it is that it was brute forced. The administrator account username had been ...
0
votes
1answer
18 views

Fibonacci LFSR, recovering previous bits

Suppose somewhere is Fibonacci LFSR, we know that it has 7 cells and feedback taps are cell 2 and 7. We intercepted part of a stream, and part intercepted is 1010101. Is it possible to recover ...
0
votes
1answer
39 views

Confusion regarding computing Multiplicative Inverse Modulo P?

May be a silly doubt, please rectify my confusion regarding below problem: For concreteness assume $g=2, p=11, a=6$ and $x=9$ $$A = g^a \bmod p = 2^6 \bmod 11 = 9$$ $$X = g^x \bmod p = 2^9 \bmod 11 ...
0
votes
3answers
110 views

Let $G$ be a PRG. Are the following $G'$ constructions based on $G$ necessarily PRGs?

$G$ is a PRG where $|G(s)| > 2 \cdot |s|$. $G'(s) = G(s0^{|s|})$. $G'(s) = G(s_1...s_{n/2})$, where $s = s_1...s_n$. My question here is whether my own proposed solutions are correct and do ...
0
votes
2answers
179 views

How is message length involved in public/private-key encryption?

I've just read this question regarding why to sign only the hash of a message. I kind of understood the answer, but the question arisen is now: Why can I encrypt any text messages with the same ...
0
votes
1answer
42 views

Trying to understand the constant factors (19 and 38) in Ed25519 ref10 function 'fe_mul'

I would like to transpose the Ed25519 ref10 implementation to a similar twisted Edwards curve that is based on another prime, in order to have the same speed optimizations in place for the new curve. ...
0
votes
1answer
349 views

How to crack SHA256 only letters

I recently created a program that hashes a password using SHA256 and potentially using salt. How can I crack that if I know that the password only contains lowercase letters?
0
votes
1answer
99 views

ElGamal scheme attack when one message is known and ciphertexts are intercepted

Let $G$ be a finite cyclic group of order $p$ and let $pk = (g, h=g^a)$ and $sk=(g,a)$ be Bob's ElGamal public/secret key pair in $G$. To encrypt a message $m$, a random number $r$ is selected and a ...
0
votes
2answers
60 views

Getting the encryption/has algorithm used for modem configuration file [closed]

Hello guys I have backed up my modem configuration file and found the username and password is in clear text; the files shows the username and the password is : ...
0
votes
1answer
228 views

what are the most common stream ciphers algorithms? [closed]

say that we have an unknown stream cipher which output bytes and which have more than 10 years of existence. What can be the most probable algorithms if we consider the most 'populars' stream cipher ...
0
votes
1answer
69 views

Encryption(AES) and verification per message

I want to send/receive messages with A (an peer) using TCP socket. I want to encrypt messages using AES CBC. Only I and A know a symmetric key K1 used in AES CBC, and K2 used in HMAC. The size of each ...
0
votes
2answers
3k views

simple algorithm to encrypt/decrypt a text file

I need to write a first program in one language that saves data in a text file, and write a second program in a second language to decrypt that file. The two languages in question don't include any ...
0
votes
1answer
60 views

What is the proper usage of GCM nonce in TLS1.2?

I have written a program with the help of the bouncy castle for C# library. I am monitoring the traffic which is send between the client and the server and found something (i find) strange. The ...
0
votes
1answer
83 views

How hard is it to recover $p$ if I can get $h(p) \oplus h(p^*) \oplus r$ and $h(r)$?

Assume that $h:\{0,1\}^* \rightarrow \{0,1\}^\lambda$ is a cryptologic hash function, $r$ is taken randomly from $\{0,1\}^\lambda$, $p$ is a low-entropy password and $p^*$ is a guess. Now we get $h(p) ...
0
votes
2answers
283 views

Operation modes of block ciphers how are used?

I am studying about different operation modes of block ciphers my question isn't something specific to that, but is how these operation modes are used in cryptography? I have this picture here ...
0
votes
1answer
1k views

PGP public RSA key format

I have been trying to use Go (I could post the code, but I think I posted enough already...) to generate a PGP RSA key. However every time I try to encrypt something with it, something fails. However, ...
0
votes
1answer
219 views

How to calculate RSA CRT parameters from public key and private exponent

Given the public key (n, e) and private exponent (d), how to calculate CRT parameters (p, q, dP, dQ, and qInv) of this RSA key pair?
0
votes
1answer
54 views

Break El-Gamal Algorithm by knowing the value of the random k

In El-Gamal Algorithm, the public key is $(p, g, A)$, and the secret key is $(a)$, in order to encrypt some data, the sender generate a random $k$, where: $(C_1, C_2) = (m.A^{k} \pmod{p}, g^{k} ...
0
votes
1answer
73 views

How do we know one-way functions can be iterated?

Suppose we have some one-way function $h$. Without further specification of $h$, how can we be sure that we can define another function $g(n) = h(h(n))$? That is, how do we know the range of $h$ is a ...
0
votes
2answers
694 views

Modifying a [CRC32] checksum protected file [closed]

I dont want to ask for help without showing how far I came by myself, so this is what I have so far: The file of interest is an encrypted/obfuscated .bin script, which cotains information on certain ...
0
votes
2answers
202 views

Why does Diffie-Hellman need be a cyclic group?

Why is Diffie-Hellman defined on a cyclic group? Doesn't it work for any commutative operation which the inverse is hard to find? Say Alice and Bob agree in a public prime $c$ and both choose a ...
0
votes
1answer
93 views

Why Might XOR's Lead to Hash Functions Lacking 2nd Pre-image Resistance?

My hash function is as follows: Cut the string in half (assume even length of 2m) XOR's the two halves together Take the result of the XOR and pass it to a function (a one-to-one and "onto" ...
0
votes
2answers
87 views

Looking for encryption algorithm not subject to known-plaintext attack with IV reuse

I've encountered an interesting problem where we can basically say the following: We need to encrypt messages, but we have no room to store IVs. We can synthesize IVs; however an attacker would be ...
0
votes
1answer
70 views

Adding a Random component to CBC MAC in order to enlarge the tag space

CBC MAC that is using AES as the underlying block cipher, has tag space of 2^128. If we add a random single block, concatenating it with the tag, and encrypt it again in AES CBC mode, with additional ...
0
votes
1answer
72 views

SSL certificate / SSL configuration - FIPS-197 compliance

What does it mean when we talk about FIPS-197 compliance in the context of SSL certificates, their deployment and usage ? I am almost certain that the FIPS-197 compliance in the context of SSL ...
0
votes
1answer
93 views

Are keys generated by the user or block cipher algorithms themselves? [closed]

We know block cipher algorithms. In the block cipher algorithms, Key Scheduling is the one crucial part. I see that in some simulation programs of the AES,DES,TripleDES encryption algorithms. In ...
0
votes
1answer
170 views

Finding Vigenère cipher key(s) [closed]

How can we find the key used with a Vigenère cipher in small number of steps? If we have text like: Peit Wokm! Mhfa fepatgb ets bvvrvxmea ebte bae twkd qiqi ...
0
votes
1answer
426 views

SSL / TLS digital signature exchange

If server is sending its digital signature, in which message / where does the digitally signature is provided to the client. Is it after the server_hello message because there the public key of the ...
0
votes
1answer
70 views

Rationale of “r” AES key use in OTR version 3 AKE protocol?

I just tried to review & understand AKE (Authenticated Key Exchange) protocol as defined in OTR secure messaging protocol version 3 here , and aiming to achieve Perfect Forward Secrecy I am a ...
0
votes
1answer
465 views

AES Mix Columns and Shift Rows

Why we use Mix Columns and Shift Rows in AES? FOr example, if i want implement an AES algorithm without Mix Columns and Shift Rows what is the difference in the ciphertext?
0
votes
1answer
813 views

What do I use as the encryption key and initialization vector in AES cfb128

I'm writing a program that can encrypt a file using AES cfb128 (using Openssl and C++). The scenario of the program is this: Person A visits computer, encrypts a file they make, takes away a key ...
0
votes
1answer
80 views

AES inversion operation in sub byes

I was wondering why in the AES sub-bytes operation one can represent the inversion as computing $x^{254}$. What is the reason for this? Moreoever, I was wondering what the text on page 212 of ...
0
votes
1answer
102 views

anonymous signature implementation and usage?

This is one of the question asked in my class. Implement a anonymous digital signature. So it means hiding signers information. i could not find any article in anonymous digital signing. Also another ...
0
votes
1answer
4k views

How to decrypt a '.enc' file that has been encrypted with RSA using a public key? [closed]

While solving a CTF challenge online, I came across a situation where I needed to decrypt a '.enc' file that has been encrypted using someone's public key. The ...
0
votes
1answer
38 views

Identification by RSA

Suppose we have identification scheme as such: Bob takes random $r$, and encrypts it with Alices public RSA key $(n,e)$, sends $r^e$ to Alice. Alice decrypts $r$ and sends it back to Bob, becomes ...
0
votes
3answers
265 views

Is the keystream transmitted with the ciphertext when a stream cipher is used?

When a stream cipher is used and a keystream is generated to be XOR'ed with the plaintext, is the keystream sent with the ciphertext so that the receiver knows how to decrypt it? Or does the ...
0
votes
1answer
89 views

Blum primes [x=3(mod 4)] zero knowledge proof?

Lets say we have 2 primes, $p \equiv q \equiv 3 \pmod{4}$, and we make $n=p \times q$ public. I can, without revealing factors, show that $n$ has two prime factors. How can i zero knowledge prove ...

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