# All Questions

1answer
53 views

### Does SRP reduce to DH key echange when shared password is not secret?

I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later. I ...
2answers
151 views

### Finding hash almost-collisions

A few months ago, XKCD posted a challenge to find a plaintext which hashed (using Skein 1024 1024) to a specified value. Inputs were scored based on the hamming distance between the hash of the ...
2answers
91 views

### How to do a literature search

How do I do a literature search of the research literature on cryptography? Assume there's some topic in cryptography I'd like to learn more about; how do I search the cryptographic research ...
1answer
68 views

### Cryptography based upon neural networks [closed]

I would like learn about use neural networks in cryptography. Is there any research literature on this subject? What should I do to learn about the subject? I am taking short course in neural ...
1answer
39 views

### Is the DES algorithm in OPENSSL random?

Look at the hex dumps of encrypted1.bin and encrypted2.bin . They both have same password A which was used to encrypt sampletext ...
1answer
76 views

### Security of Salsa20 with some known plaintext?

Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known? Assume that a different IV and Key are generated before each file is ...
1answer
176 views

### What does $(\mathbb{Z}_n^*)^2$ mean?

In a paper they write once, $(\mathbb{Z}_n^*)^2$. Is this the group of quadratic residues or is it something else? Here the theorem: Under the strong RSA assumption, given a modulus $n$, along with ...
2answers
102 views

### Does knowledge of original file size provide a cryptographic weakness?

I'm encrypting files using an AES-256 CBC cipher and an SHA-256 HMAC every 64KB in the file. Since AES CBC needs an amount of input bytes to be divisible by 16, I use PKCS#7 padding to bring the ...
1answer
87 views

### Given a certain entrophy per character, how long should a passphrase be to guarantee key strength?

Given an entrophy of 1.5 bits per character, how long does a passphrase have the be to guarantee a key strength of a 128 bit random key? Assuming an alphabet of 26, one character takes log2(26)=4.7 ...
1answer
92 views

### Winzip AES256 vs PGP

If I use the AES256 option in Winzip to encrypt a file, is it any less safe or less secure than using pgp encryption?
2answers
201 views

### Custom crypto library in C

I will be making (in the near future) an app that will contain some pretty heavy crypto. As it is possible that my app will be ported to different devices (initially it will be iOs only, but Mac, ...
0answers
27 views

### Decrypting TLS in Wireshark when using DHE_RSA ciphersuites [migrated]

How can I decrypt TLS messages when an ephemeral Diffie-Hellman ciphersuite is used? I am able to expose the premaster secret and master secret from the SSL Client. Using that, how to decrypt the ...
2answers
84 views

### encrypt message with one digest 0-9 instead of 01-26

How much will the security of one-time pad decrease if I use one digit from 0-9 instead of 1-26? for example plaintext = "blue" and ...
1answer
143 views

### CBC-MAC , fixed length, all blocks returned

CBC-MAC, with fixed length message. Is it safe to return all ciphered blocks instead of the last? My intuition says it is less secure, since is gives an attacker more information. But how could one ...
1answer
44 views

### How to derive formulas for addition and multiplication in Jacobian coordinates

Is there a way to derive the formulas for point addition and multiplication on elliptic curves in Jacobian format by yourself? How could I have derived these formulas by myself?
1answer
101 views

### Recommended way of adding a pepper/secret key to password before hashing?

There have been several questions regarding password hashing here and on Security.SE. A "pepper" is sometimes mentioned – an application-specific secret key. The canonical answer on password hashing ...
2answers
149 views

### RSA leak bits to factor N

Suppose you randomly generate large primes p and q as in RSA, and then tell me N=pq but not p or q. Then, you would like to actually let me factor N, except you should tell me as few bits of ...
1answer
81 views

### What length should the padding be when encrypting or signing with RSA?

Does it matter what length the padding is? If so - what length should it be? (Another point: Should it be random?)
1answer
63 views

### Weak One Way Function

Show The function $mult(a,b)$ is weak one way if the Integer Factorization Assumption is true. I am read the proof of this enunciated but I want know if I understand this in my way. The proof use the ...
2answers
172 views

### AES - plaintext is smaller 128 bit - how to expaned?

we are currently developing a little AES implementation in a crypto-course at university. As far as I know, AES uses 128 bit blocklength, so all data that will be encrypted will get split up into ...
2answers
70 views

### Many consecutive hashes to slow down brute force attack?

I've heard that hash algorithms like bcrypt are more secure because they take longer to complete, and therefore take much longer to prute force, without a noticable ...
1answer
94 views

### Injecting salt into PyCrypto KDF - useful?

I have noted some sources indicate that when using a KDF like PBKDF2 (alternatively) some advocate injecting the salt at the time of execution - like this: ...
1answer
58 views

### How to hash a structure that needs to include that hash's outcome?

so I am busy writing a TCP protocol in which I send a "packet header" with each packet of data. This packet header is a structure that contains information about the data that was sent. I want to ...
0answers
62 views

### RSA Encryption Sckeme [closed]

Can anyone help me with this question? A and B want to exchange encrypted messages; specifically, B wants to send a message M written in binary format to A, which needs to be encrypted. They agree on ...
3answers
895 views

### What should be the size of a Diffie-Hellman private key?

I'm implementing the SRP-6 protocol, which relies on discrete logarithms for it's security (essentially Diffie-Hellman). The RFC documents state: The private values $a$ and $b$ SHOULD be at least ...
1answer
98 views

### Are digital signatures secure for signing lots of small messages?

I need to sign the numbers from 1 to 1 billion (literally this, it's not an analogy) using a digital signature and then send these numbers in a particular order to someone. The message is not private ...
3answers
162 views

### Implementing secret reconstruction in Shamir's Secret Sharing

I am trying to implement Shamir's secret sharing in C++. I have got the generation of shares working. However, I am very confused with the reconstruction of shares. I get the part on how three users ...
0answers
46 views

### 2 ciphers to solve [closed]

I need to solve these two ciphers: 1. ...
1answer
61 views

### Attacking AES/CCM with random IV

A cryptosystem is using AES-128 in CCM mode with random IV. Suppose an attacker capable of: asking the cryptosystem to encrypt a single plaintext as many times as he wants; and asking the ...
4answers
418 views

### How do you find a cheater in Shamir Secret Sharing?

If there are 4 people involved, and every two of them should be able to know the secret (the polynomial is just a line) and you are given f(x) and x for each of those people, and you know one of them ...
1answer
110 views

### Indistinguishability attack example

I want solve the next exercise. The author defined the experiment for the cryptosystem $\Pi$, the adversary $A$ and the security parameter $n$ as follows $\mathsf{PRIV_{EAV}}(\Pi,A,n)$ The ...
1answer
46 views

### Solving a discrete logarithm using GDlog

I am trying to calculate an x, such that t = g^x mod p (I need to crack a weak elgamal encryption for university). I found gdlog, but I cant figure out how I can use the input to calculate my x. Here ...
0answers
53 views

### What is a CBC Mac Scheme? How does knowing one block release other? [closed]

I guess CBC-MAC encryption relies on the previous block for encryption but how does knowing intermediate block cipher output make it insecure?
2answers
235 views

### Is there an algorithm for factoring N, which is just as simple as this one, but faster?

I found a simple algorithm for factoring semiprime numbers, you can read about it in Factoring Semiprimes and Possible Implications for RSA. It basically works like this: You reverse the digits in ...
0answers
61 views

### Show that for all integers n>2, n does not divide n^2+2 [closed]

I believe this solution can be solved by induction, I just don't know how to phrase it recursively. For all n>2, n^2+2 mod n ≠ 0 Base case n=3 3^2 + 2 =11 11 mod 3 = 2 ≠ 0. Show that (n-1)^2 +2 ...
2answers
151 views

### What's the difference between AES and earlier block ciphers?

Is there any difference except speed and key and block size from user's point of view? Or does AES have something that ideal block cipher doesn't have?
2answers
119 views

### How to derive two keys from one password

What is the best way to generate two independent symmetric keys from one user-entered password or passphrase? Would using both scrypt and pbkdf2 achieve this?
3answers
102 views

### how much is secure to encrypt a password using itself (as encryption key) for storing it on a unsecure media?

I want to store a password securely on a storage (suppose in a usual unencrypted file). I use this password as AES key to encrypt itself (using AES-ECB) & then store it on the media (the password ...
2answers
899 views

### Is the following statement about PRG true or false?

Is the following statement true? If $G: \{0,1\}^k \rightarrow \{0,1\}^n$ is a PRG, then so is $G':\{0,1\}^{k+l} \rightarrow \{0,1\}^{n+l}$ defined as $$G'(x.x')=G(x).x'$$ where $x \in \{0,1\}^k$ and ...
1answer
99 views

### Why SRP is not widely used?

SRP seems to be a very good password authentication protocol, compared to any other things used now. So why is there no popular implementations, or even no working secure implementations? I tried to ...
1answer
67 views

### Elliptic Curve is DH function or PKI?

can we reuse same ECC key on TLS for long terms or it must be used just once? (i mean can we use ECC like RSA?) is there patent free ECC implementation ?
2answers
90 views

### Is there any strong enough pen-and-paper or mind cipher?

Some ciphers are talked about here, but I don't see an answer, are they strong enough, or are non-computer ciphers more or less just a toy and one should abandon using them for practical purposes?
4answers
1k views

### How can rainbow tables be used for a dictionary attack?

I'm putting together a password policy for my company. I very much want to avoid requiring complex passwords, and would much rather require length. The maximum length I can enforce is 14 characters. ...
2answers
130 views

### Have I understood pedersen commitment correctly?

I want to do a one-sided integer commitment scheme. I.e. the whole process must be non-interactive where I at one point first publicly reveal some data and then at a later time reveal the committed ...
0answers
37 views

### DES chosen-plaintext attack in Windows [closed]

How do I do a DES chosen-plaintext attack in Windows?
0answers
85 views

### Adding and multiplication in jacobian coordinates

How can I derive formulas for adding and multiplication of 2 points in Jacobian coordinates $(x,y) = (\frac{X}{Z^2},\frac{Y}{Z^3})$ over an elliptic curve?
0answers
34 views

### session keys in an online e-voting system [closed]

I do not have much knowledge about cryptography or public and private keys, and your help will be much appreciated. I am totally a beginner, and no one from my university can help me. I am trying to ...
1answer
92 views

### Attacking historical ciphers methodology

It's more a theoretical question of how would you approach it. All you know about the ciphertext it's was generated with a historical cipher. The ciphertext appears to be random, BUT it's divided into ...
1answer
42 views

### recommendation for steganography tool? [closed]

I am trying to find a good and referenced steganography tool to make some tests, it its freeware it would be great. Does anyone knows any recommended tool for this task? I have found some free ...
2answers
778 views

### What is the most practical fully homomorphic cryptosystem?

Craig Gentry recently gave the first fully homomorphic cryptosystem. Quite a bit of work has been done since extending his work. It seems, however, that no system is practical for real world use. ...

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