# All Questions

227 views

### What is “witness encryption”?

I recently skimmed over tho papers on time-lock encryption: “Time-release Protocol from Bitcoin and Witness Encryption for SAT” by Liu, Garcia, and Ryan “How to Build Time-Lock Encryption” by Jager ...
27 views

### Relationship between an elements order and the DLP [closed]

How can I use these properties to attack the DHKE? I know that the order of $a$ is always $2$ for $a = P - 1$ in $Z_p$. The subgroups generated by a will be $\{1,a\}$.
137 views

### Turning a 64 bit block cipher into a 128 bit block cipher

There are quite a few block cipher modes of operation that require 128 bits. There are also modes of operation where a higher block size than 128, e.g. a block size of 256 bit would even be practical. ...
111 views

### 3DES over Galois Counter Mode (GCM) for authenticated encryption

Is it possible to use DES or 3DES over Galois Counter Mode (GCM) to provide authenticated encryption? I haven't seen any implementation yet.
62 views

### Encrypt a file for multiple persons with different keys?

I thought a problem and want to ask if there's a more elegant solution. The scenario: A company with a fileserver, which hosts encrypted documents. The files need to be accessible by about a dozen ...
141 views

### Session key Exchange, some doubt

I have to find a solution to this problem: I have a network composed by 1 server and some client. The server has a couple of keys (public and private) and it shares a secret key with each client. My ...
86 views

### Concerns about use of MAC in my specification

Here is the pseudocode for a routine I am designing: ...
1k views

### What are the differences between collision attack and birthday attack?

From my understanding both types of attack, collision and birthday, are based on the principle of two randomly/pseudo-randomly chosen plaintext to hash to the same value. I don't want to launch any ...
743 views

### what are the advatanges and disavantages of the digital signature algorithms for JWT?

I am using a Java JWT library jose4j. There is a list of digital signatures algorithms which can be used. HMAC using SHA-2 RSASSA-PKCS1-V1_5 Digital Signatures with with SHA-2 Elliptic Curve Digital ...
69 views

### Encryption(AES) and verification per message

I want to send/receive messages with A (an peer) using TCP socket. I want to encrypt messages using AES CBC. Only I and A know a symmetric key K1 used in AES CBC, and K2 used in HMAC. The size of each ...
27 views

### Compromised Issuing CA [closed]

I'm configuring a PKI infrastructure with an offline root CA and several issuing CAs. Among other topics, I'm struggling to decide how the revokation of an Issuing CA certificate works. My Root CA ...
134 views

### Why develop Edward curve formulas that deviate from unification?

Edward curves were considered initially because they provide a unified formula for both doubling and addition, thus having inherent side-channel resistance. But a lot of work has been done recently ...
62 views

### is this possible to use asymmetric encryption schemes as order preserving encryption

Are we able to use order preserving encryption in asymmetric schemes, is this work efficiently. is this secure at any one of the situations
74 views

### How can complexity be increased or decreased in AES?

I have been studying data compression for a while. For educational purposes, after a lot of reading, I managed to create a software that performs encryption and authentication using AES256-GCM. ...
31 views

### Voting protocol - How many dishonest tallying centres can the protocol cope with?

We have the voting protocol that is described here. I am looking at the following exercise: Determine how many dishonest tallying centres the protocol can cope with before the following properties ...
50 views

### Establish Trust By Signing Random Seed

I'm trying to get my server to establish trust with a client. Neither is on the Internet, so there are no certificate authorities. The typical way to establish trust in my domain is for a client to ...
72 views

### What does the acronym “CRT” stand for in the PKCS #1 specification?

What does the acronym "CRT" stand for in the PKCS #1 specification? Does it stand for "Chinese Remainder Theorem"? Thanks, Pete
595 views

### What's the structure of server-key-exchange message during TLS handshake

Here is a relevant question: With OpenSSL and ECDHE, how to show the actual curve being used? Using ...
126 views

### Proof that two parties can communicate

Suppose we have three parties, Alice, Bob, and Carol. Alice can receive messages from Bob and Carol individually, but can only send messages to both simultaneously. Additionally, Alice cannot tell if ...
112 views

### Can I use an ECDH Shared Secret from the same Private / Public Key Pair?

I'd like to know if using the ECDH shared secret of a static EC Private Key with it's own corresponding static EC Public Key causes a problem / weakness. (edit) not asking if it's ok to re-use the ...
216 views

### How HMAC.Update function works?

I know how standard HMAC(key,msg) function works, and I want to write a Delphi port of HMAC class that implements Update function. The problem is that I don't understand how this Update function works ...
7k views

### SHA512 faster than SHA256?

I'm getting this strange result that SHA512 is around 50% faster than SHA256. I'm using .net's SHA512Managed and SHA256Managed ...
135 views

### What is difference between Cryptographic Transformation, Encryption and Hash? [duplicate]

I read in a book that: let $f(K,R)$ is cryptographic transformation of $R$ using $K$, $K\{R\}$ means $R$ is encrypted using $K$ and $h\{R\}$ is the hash of $R$ and then the example follows. I want to ...
207 views

### How to generate own secure elliptic curves?

I know that the algorithm used to generate the Brainpool curves and the NIST curves is published. The algorithm should be this one (RFC5639 Appendix A). From what it looks like it's rather slow to ...
125 views

### EC: Why does $h>200$ need to hold?

From BSI-TR-03111 (PDF), on page 15: The class number of the principal order belonging to the endomorphism ring of E SHOULD be at least 200. This value commonly is referred to as $h$ in that ...
163 views

### What are the differences between the elliptic curve equations?

I think we're all aware of the "classical" Weierstrass (short?) elliptic curve equation: $y^2\equiv x^3 + ax +b \pmod p$. Well known examples of these curves include the NIST's and Brainpool ones. ...
I was reading about the Linear Feedback Shift Registers and I am confused about the technique to find the period of a primitive polynomial. Consider the polynomial $x^5 + x^2 + 1$. As this is a ...