# All Questions

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### AES decryption vs encryption speed

Let's consider the CTR mode. For a faster encryption/decryption, is it preferable to use the decryption operation of AES, or its encryption ?
12 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 ...
18 views

### Deriving message from signature (RSA)

Usually signatures are used for verification, and this requires that you pass both the message and the signature. I was wondering; if the message holds to a certain format (for example, valid json ...
5 views

### OpenSSL ECDH key exchang mechanism

I am using FIPS based OpenSSL module for encryption of sensitive data for my desktop socket server and client applications. I am using ECDH for key agreement.The keys public and private pair is ...
11 views

### Starting point on Fully Homomorphic Encryption and Proxy Re-encryption

I am new in this field. Can some one tell me where should I start for FHE and PRE reading ? Any papers where I can find Basic information on FHE and PRE ? Thank You in advance.
911 views

### Perfect zero knowledge for the Schnorr protocol?

Can somebody explain (or point to a reference) why the Schnorr protocol cannot be proved zero knowledge?
11 views

### Anonymous messaging using blind signatures

I want to implement a message relay server that knows nothing about who has sent a message but at the same time maintains a message quota per user. While searching for ways to do that on the internet ...
79 views

### Proving set membership in less than log(N) bandwidth

I have an unchanging set of unique items, and I want my server to show one of those items to a client, then cryptographically prove that the item is part of the set. How I do this currently: ...
12 views

### Assuring Client is Authorized to use JSON Web Token

JSON Web Tokens ( JWT ) are server-signed objects that the issuing server uses to identify a user, track session data and authorize requests. The fact that JWT are server-signed gives assurance that ...
214 views

### What is stopping someone from saving encrypted info, and decoding it later?

When I send encrypted data to a website, using public key encryption, what is stopping someone who is listening from storing my encrypted data, and decryption it in a few years after they have ...
131 views
+100

### Key Size for Symmetric Homomorphic Encryption Over the Integers

In the paper Fully Homomorphic Encryption over the Integers, it mentions a symmetric key scheme on page 1 and 2. Key Generation: Pick a random odd number $p \epsilon [2^{N-1},2^N)$ Encrypt A Bit m: ...
29 views

### Why Curve25519 for encryption but Ed25519 for signatures?

NaCl and libsodium libraries use Curve25519 for authenticated encryption (actually for sharing a key which is used for encryption) and Ed25519 for signatures. What is the purpose of using different ...
7 views

### How do I encrypt a PGP message through java's crypto extension? [migrated]

Currently I'm using bouncy castle's libraries for the actual work and have found an example at sloanseaman.com that (after a little tweaking) works with v1.52. I've also got a working example from ...
80 views

### Is there a secure source of entropy on a typical microcontroller?

On a device that does not have a hardware RNG, what is the best source for entropy? Some options and pitfalls floating around: Use the ADC to read something analog: can become deterministic if ...
27 views

### Attribute Based Encryption [duplicate]

Could someone explain the main differences between Key Policy Attribute Based Encryption (KP-ABE) and Ciphertext Policy Attribute Based Encryption using an example? I know that KP-ABE depends on the ...
49 views

### POODLE attack on TLS 1.2

The POODLE attack uses the way block ciphers in CBC mode are decrypted in combination with the packet's padding to determine some byte's value. From what I understand, even TLS 1.1 can be vulnerable ...
43 views

### What is the impact of a server not fully verifying the data in the Client Finished packet of a TLS connection?

F5 BIG-IP devices suffer from a vulnerability in which not all bytes of the Finished packet in a TLS connection are validated. The sort-of technical description can be found here. F5 don't consider it ...
138 views

### Using a hash (like SHA-256) vs AES as the source for pseudo-random values in Feistel network?

This question is in relation to Wikipedia article on Format Preserving Encryption It says the following It is also possible to make a FPE algorithm using a Feistel network. A Feistel network ...
30 views

### Test for randomness

Suppose I have a data set provided by PRNG in a matrix form with 400,000 rows and 20 columns. Each row consists 20 unique integer values from 1 to 80. I need to check the goodness of the PRNG. For ...
21 views

### Hash-values's length in identification schemes

I am trying to understand the impact of applying a hash function in an identification scheme. It makes reference to the publication "On the length of cryptographic hash-values used in identification ...
91 views

35 views

### Can a block cipher encrypt the message to itself (plaintext equal to ciphertext) [duplicate]

The result of the cipher should be indistinguishable from random, but can it happen that cipher produces the ciphertext that is equal to the plaintext as it also lies in the corresponding space? I ...
781 views

### CBC - a canonical mode, even though there are streaming modes

Why is CBC considered the canonical mode when there are streaming modes available such as CFB and OFB? One thing that I can think of is that in CBC you can easliy do range-based decryption. All you ...
59 views

### Where is CFB-MAC defined?

I can find a couple of descriptions of using CFB mode to create a MAC, but cannot find any standard or papers analyzing its security bounds. Is there a standard for CFB-MAC? Where can I find an ...
40 views

### Chosen plain text and chosen ciphertext definitions clarification

I am trying to understand a concept of CPA and CCA attack and I cannot get one thing from the definition. If an attacker can execute a CPA attack for something like Send 100 dollars to attacker that ...
71 views

### Is there really any way to nullify or avoid MITM attacks?

The question pretty much sums it up. Is there any way to make an attacker who is successfully performing an MITM attack to actually not be able to read or change the messages? Assuming there is no ...
27 views

### In HMAC-MD5 Implementation, why “i_key_pad” and “o_key_pad” if They Are Public and Constant? [duplicate]

Please Consider: English is My Second Language This Wikipedia article on HMACs shows a part of a HMAC-MD5 implementation making use of i_key_pad and ...