# All Questions

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### Reversing SHA1 (don't know the correct term)

Given sha1(pad(A) || pad(B)), where B is known, can I calculate sha1(pad(A))? pad(A) means its length is exactly 1 block (64 bytes for SHA-1) If yes, for which other hash functions it will work too? ...
103 views

### Acceptable assumptions when prooving security

Considering the output of a cryptographic primitive, like an encryption scheme (CBC, ...), a hash function or even the output of any schemes based on number theoretic assumptions, is it reasonable ...
56 views

I need an implementation of linkable ring signature, a ring signature which allows identifying whether two signatures belong to the same signer. It has important privacy-related applications, like ...
46 views

### can we do double encryption of a message without first key?

Lets assume $k_1$, $k_2$ are two keys and there can be any relation between them like $k2 = E(k1)$ that is key $k_2$ is encryption of $k_1$ using some other long term key or any other relation. ...
188 views

### Do recent announcements about solving the DLP in $GF(2^{6120})$ apply to schemes proposed for cryptographic use?

A recent paper by Göloğlu, Granger, McGuire, and Zumbrägel: Solving a 6120-bit DLP on a Desktop Computer seems to "demonstrate a practical DLP break in the finite field of $2^{6120}$ elements, using ...
814 views

### How robust is discrete logarithm in $GF(2^n)$?

"Normal" discrete logarithm based cryptosystems (DSA, Diffie-Hellman, ElGamal) work in the finite field of integers modulo a big prime p. However, there exist other finite fields out there, in ...
90 views

### How to test if a number is a primitive root?

How to test if a number is a primitive root, assuming the modulus is a prime? And if not? Is it not enough if the number is relatively prime to the modulus or prime?
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### Attacks on a stream cipher

What attacks are there against stream ciphers? I found 2: Bit-flipping attack. Since every input bit mention exactly one output bit, it is possible to change ciphertext bits where the corresponding ...
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### Could quantum computers “break” symmetric crypto-systems (e.g. AES)?

These days I'm reading about quantum computing and quantum cryptography which I've found extremely interesting. Well, I also read some blog posts of Bruce Schneier talking about how quantum computers ...
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### RSA vs El Gamal digital signature. Which is more secure?

I'm reading about the notions of security concerning digital signatures and I can't understand whether RSA is more secure than El Gamal digital signature. Well, they are both prone to forgery, but I ...
31 views

### Hardware implementation of pairing

I would like to design a hardware-based accelerator for a pairing algorithm to make it faster. I know that I need to do arithmetic over a base and an extension field. Could anyone would suggest which ...
64 views

### How well analyzed are giant block length ciphers?

I have heard about ciphers that have a block length of 256 megabytes... That is huge. How well are they understood by the encryption community? I'm referring to PMC Ciphers. Has anyone used such a ...
83 views

### Encrypt user email but be able to find user by email

Sorry for my dumb question, but it's better to ask dumb question than to do dumb things silently. I want to encrypt user email in my DB so that if someone stole the DB (and not the key) - he won't be ...
209 views

### Why is SRP 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 ...
69 views

### AES encryption with multiple keys

I would like to encrypt some data using a combination of multiple keys. There would be two keys: a client keys that would be generated for each client and a single server/application key used by ...