# Tagged Questions

Analysis of individual security aspects of a cipher or algorithm, not the security of a cipher or algorithm in general (which would lean towards “algorithm-design”).

766 views

### Exchanging encrypted messages, and decrypting without a public key?

I know very little about encryption, but I was hoping someone could shed light on this cipher text exchange scheme I worked out in my head this morning: Bob wants to send Alice a message but doesn't ...
214 views

### RSA Attack, known public key and ciphertext. Can decrypt the message m?

I'm stuck with this problem: Assume Alice and Bob are using RSA to communicate each other. Given Bob's public key $(217,7)$, Alice send the ciphertext $c=53$ to Bob through RSA encryption. Now, Eve ...
4k views

### Why can't I reverse a hash to a possible input?

I'm going to provide “proof” why a hash function can be reversed, and I hope you can tell my why I'm wrong So, a hash function can be implemented as a series of logic gates. All logic gates can be ...
255 views

### Memory-hard proof-of-work: are they ASIC-resistant?

Is a memory-hard proof-of-work scheme necessarily resistant to speedups from custom ASICS? Background: Bitcoin uses a proof-of-work scheme based on SHA256 hashing. The scheme is compute-bound. ...
89 views

### What libraries do people use to implement and evaluate cryptography protocols? [on hold]

I want to implement this credential system: “Anonymous Credentials Light” (PDF). The implementation would involve some zero-knowledge proof and some exponentiation. For some basic group computations ...
139 views

### More rounds after AES related key attack?

In his blog Schneier discusses that there is a new related key attack on 10 rounds of AES-256 "Another attack can break a 10 round version of AES-256 in 245 time, but it uses a stronger type of ...
967 views

### Feistel cipher vs Substitution-permutation network - number of rounds

So I have been doing for the last couple of days comparison between Feistel cipher and Substitution-permutation network. Now I can say I know a lot about them and their similarities and differences ...
121 views

### Is this a correct way of use symmetric encryption?

If I want to encrypt some block of text in AES, but at the time of decryption I don't have a way to check if the symmetric key is the correct one. So I: Generate a randomKey, and use that to encrypt ...
57 views

### Can the original message be retrieved from a public/private key signature?

When I sign a message (which has potentialy low entropy) using a private key and I send it without the original message, can the original message be retrieved from the signature(s)? I want to prove – ...
75 views

### Data Encryption Standard (DES) S-Boxes

I read that the S-boxes introduce the much needed nonlinear behavior to DES. Can someone give me a lay mans explanation of why the effect of the S-boxes is said to be non-linear?
112 views

### How to compare the efficiency of public key cryptosystems, i.e., RSA vs El Gamal?

As part of my Mathematics degree I'm taking a Discrete Mathematics module which partially covers Public Key Cryptography but does not at all enter it in depth. I'm currently working on a project that ...
112 views

### Managing data access through asymmetric cryptography

I want to manage authorization, as 3rd-party permissions, through asymmetric cryptography. I'm concerned about how it is possible to share access of encrypted data with N entities, be able to revoke ...
371 views

### Knowing pre-encryption data, can we find the private key CryptoWall used?

I'm just repurposing a question already asked about Cryptolocker for CryptoWall: "If we know exact contents of some of the files prior to them being encrypted, would it be feasible to use those ...
193 views

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### how to decrypt hidden text under numbers? [closed]

got a question as follows - how to decrypt below in to letters knowing that crypting language is 469 and it base ofcourse on mathematic. 46781! 9063376290 3222011 677 80322429 67538 14805394, 6880326 ...
94 views

### Find plaintext from two ciphers encrypted with a one-time pad and the same key

I'm studying for a cryptography test and I came across this question: Assume a language has three letters: A=1111, B=0011 and C=1010. Two words in this language are encrypted with a one-time pad ...
247 views

### Can Grover's Algorithm be combined with a meet-in-the-middle attack?

We all know and love the meet-in-the-middle attack which basically makes double encryption pointless using a time-memory-tradeoff. Now there was recently the recommendation by the NSA to use double ...
52 views

### What is the most an adversary can do in the context of public key masquerading?

Suppose two parties A and B are using a public-key encryption scheme in order to communicate securely. A and B both have a public/private key pair: $$A: (P_A, S_A), B: (P_B, S_B)$$ and A already ...
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### Carrying out a known-plaintext attack on a cipher [closed]

Previously posted here. Someone suggested I could post it here to get some answers. I am trying to solve a CTF challenge, here. Basically we're given message and key inputs to a cipher and its ...
357 views

### Deciphering “easy” ciphers without hints

I've been keen on IT Security for a long time now and I've learned a lot about networking & security. However trying a "decryption challenge" I'm lacking what I think is basic encryption/...
86 views

### Output of using the same key in all 3 boxes of 3DES

I am trying to figure this one out: What would be the encrypted output for an input x if the same key K is used in all three boxes of 3DES? The encryption scheme for 3DES with three different keys, ...