# All Questions

217 views

### Allowing the user to choose the hashing formula at the registration

I was thinking of a potential new way to increase someone's account security. The idea was allowing the user to choose one of the hash formulas available in the software (example: "MD5", "SHA512" and ...
198 views

### Is the polynomial reconstruction problem really “intractable”?

In the family of the believed (experts haven't come yet with a solution) intractable problems in cryptography belongs the Polynomial Reconstruction problem in which an attacker is given $n$ points in ...
694 views

### SIMON implementation, decryption issues

I've been trying to implement the new SIMON block cipher in Ruby as a personal challenge. The spec didn't include a pseudocode version of the decryption but I thought I had it figured out. The code I ...
231 views

### What's the most secure way to derive a key from a password repeatably?

I'm trying to write a cloud storage application where everything the user uploads is unreadable by the server, encrypted client-side before being sent. Currently, the flow looks like this: User ...
454 views

### Encrypted counter as IV in CBC mode encryption using same key

I'm currently working with a secure transport protocol that defines the IV to be a counter (incremental nonce) to be encrypted with the same key. This is a followup to a protocol that did not provide ...
98 views

### Signing an integer, which may be increased

I have a 64 bit integer. It has some sort of signature so that one can be sure it is valid. Anyone may increase the integer, update the signature, and remove all trace of the old signature. But it is ...
836 views

### What is U2FsdGVkX1?

Using CryptoJS 3.1 I noticed that using 3Des, the encrypted message always start with U2FsdGVkX1 Why is the first part of the encryption always the same? What information does this hold and ...
1k views

### How do I decrypt ciphertext with this cipher?

I have an encryption function $$E(p) = (ap + b) \mod{26}$$ where the parameters are $a=7$, $b = 10$, and $p$ is the plaintext letter. I was asked to decrypt the ciphertext ...
229 views

### Proofs of security methodologies

I'm looking for course material on the subject of proofs, reductions, and games, as used to prove cryptographic schemes secure. What are the methodologies? What are the preferred ones? In what cases ...
106 views

### Can substrings of a long string be efficiently authenticated?

Suppose one has a (strong) shared secret key and wishes to authenticate a very long string in a way that will allow the verifier to verify small substrings without reading much of the stored data and ...
189 views

### differential and linear cryptanalysis

I have been reading about differential and linear cryptanalysis. They were mainly introduced by Adi Shamir and Biham to show weakness of DES. However, many of articles state that they have been ...
273 views

### Alternatives to HMAC + CBC?

I'm looking at using HMAC + CBC. The combination looks like this: ciphertext = AES256(text, k1) data = HMAC-SHA256(iv | ciphertext, k2) | iv | ciphertext Where: ...
139 views

546 views

### KeeLoq showing that decryption is indeed the inverse of encryption

In some text I am reading, there is an exercise asking to show that KeeLoq decryption function is the inverse of the encryption function. Details about KeeLoq are given in the Wikipedia article. As I ...