# All Questions

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### How to calculate elliptic curve parameters?

I'm having a rough time understanding the math behind elliptic curves. I want to implement ECDH where user can define a, b, and p parameters of elliptic curve. How can I calculate generator base ...
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### On the fly signatures and zero-knowledge

I am reading some articles which explain on the fly signatures (also called online/offine signatures). The principle is that a few operations do not depend of the message we want to sign, so these ...
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### Encrypted Data length in a CBC Block Cipher

The RFC5246 states the following: The encrypted data length (TLSCiphertext.length) is one more than the sum of SecurityParameters.block_length, TLSCompressed.length, ...
9 views

### Using Skein as PRNG

I have read that the skein hash can be used for quite a few different functions, including a PRNG. Would using the 1024 Skein hash to return 16KB of data be appropriate for a PRNG? Or would it only be ...
13 views

### PRF and pairwise independent hash function

I'm confused with the concepts of pairwise independent hash function and pseudorandom function. They seem identical to me. A family of hash functions $H=\{ h:U \to [m] \}$ is $k$-independent if for ...
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### What procedure to use to verify a raw public key (TLS ECDHE_EDCSA ciphersuite)?

Contrary of verifying a certificate which is a well-known procedure, I am wondering what the procedure is to verify a raw public key 'certificate' (https://tools.ietf.org/html/rfc7250). This ...
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### How much of a TLS finished message is encrypted?

The client finished message is the first message that uses the newly negotiated keys and secrets. Now RFC5246 section 7.4.9 shows the message being made up of the verify data field (normally 12 bytes ...
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### How to derive a symmetric key from ECDH shared secret?

I am trying to implement the internal primitives of ECDH. Currently I'm able to multiply the receiver's public EC point with the sender's private key to arrive at the shared EC point. Next step is to ...
31 views

### have a question in the book “introduction to modern cryptography”

"introduction to modern cryptography. 2ed" in page 254 "By obtaining sufficiently many estimates and letting $x_{i}$ be the majority value, $A{'}$can ensure that $x_{i}$ is equal to $gl(x, e^{i})$ ...
21 views

### Hashing entropy with only 128 bits of internal state

I am looking to implement the Fortuna algorithm on a system with very restrictive memory constraints, using AES-128 as the underlying cipher. As the key size is only 128 bits, using a 256-bit entropy ...
19 views

### Most Secure Exchange of Keys [on hold]

Given both Alice and Bob must exchange IP addresses to perform such an operation, what is the most secure way Alice and Bob can exchange public keys between two mobile devices without having to rely ...
44 views

### CBC-MAC just to verify integrity

I have a message and I want to verify its integrity and authenticity. I have a shared secret (key) that is not used for other encryption. Is it safe to send a plaintext message containing all the ...
13 views

### Where is Signaturevalue in Certificate?

Where is the Digital Signature value in my certificate? I can find Signature Algorithm and Signature Hash algorithm. Also why there are two fields specifying the Signature's Hash? With Signature ...
15 views

### Finding Galois LFSR and its initial configuration

Suppose recursion for output of Galois LFSR is $u_1=u_3=u_4=0$ What kind of taps are here, and initial state? How to uncover this information?
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### Do $v_1=\alpha\cdot r_1$ and $v_2=\alpha\cdot r_2$ leak information about $\alpha$

Please consider we have finite field $\mathbb{F}_p$ for large prime number $p$. We have a fixed field element $\alpha$. By $r_i\leftarrow \mathbb{F}_p$ we mean we pick $r_i$ uniformly random from the ...
27 views

### Use of the IV for the CBC Block Cipher in TLS1.2

I'm struggling to understand at what point a message is encrypted when looking at RFC 5246. The spec gives the generic block cipher in section 6.2.3.2 as: ...
33 views

### Why can ssh-keygen export a public key in PEM PKCS8 format?

In the documentation of ssh-keygen (man ssh-keygen) it says for the option -m that an export ...
30 views

### Two-party generation of public and private key pair [on hold]

I was wondering if there is any kind of cryptosystem where the following characteristics are met: Both public and private keys are generated by a two-party key generation protocol between a user and ...
22 views

### Would this be considered as a challenging code to break for a crypto-professional? [on hold]

967823 967824 967845 967846 967967 967068 968189 969283 960306 962429 964543 966660
71 views

### How much processing power should you assume an attacker has?

The answer to this question says that you should assume an attacker can do one billion operations per second: Key Size for Symmetric Homomorphic Encryption Over the Integers Is that a single attacker ...
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### TLS Cipher Suite definitions

Based off the various cipher suites available for TLS (which I am looking at here:https://www.thesprawl.org/research/tls-and-ssl-cipher-suites/), can anyone clarify if when the suite contains 'SHA', ...
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### How to determine the order of an elliptic curve group from its parameters?

Let $\quad E:\; y^2 = x^3 + ax + b \quad$ be an elliptic curve defined over a finite field $\mathbb F_q$ where $q = p^n$, $a,b \in \mathbb F_q$ and $p \neq 2, 3$. By Hasse's theorem we know that the ...
12 views

### Test vectors for TLS prf function

Does anyone know where I might be able to find test vectors for the prf function in TLS? (either 1.0 or newer). I'm trying to implement a client and I am getting the BAD Record MAC return after ...
10 views

### Fibonacci LFSR, recovering previous bits

Suppose somewhere is Fibonacci LFSR, we know that it has 7 cells and feedback taps are cell 2 and 7. We intercepted part of a stream, and part intercepted is 1010101. Is it possible to recover ...
21 views

### Could eVoting on the bitcoin blockchain be done?

I'm basically a crypto noob (and not an english native), so please be indulgent :) I thought about if you could realize an eVoting system with bitcoin. I see 2 major requirements: each citizen ...
13 views

### pairing parameters in PBC library

I would like to know what are the pairing parameters of PBC library and what are they used for? Here an example where they are used. I noticed that we can give any file in the param subdirectory. Is ...
51 views

### Verify a RSA signature using only RSA encryption

I'm trying to verify a RSA signed message, however, the API that I have access to in that environment only has encrypt and decrypt. I think I understand that verification and encryption with public ...
26 views

### qkd - Does BB84 rely on a prearranged code?

First of all, sorry if the title is not that clear, I'll provide an in-depth explanation behind my question. So, basically I was reading about quantum cryptography and came across BB84. The protocol ...
20 views

### What are coding schemes for timing channels

I know we can hide information in the inter-packet delays, e.g. we can generate a code-book that each code-word corresponds to a message and is generated by realization of a specific random process. ...
30 views

### Saving energy when using public key algorithms by using block ciphers? [on hold]

When using public key algorithms like RSA, Diffie- hellman and Elgamel, how can one predict/prove/argue that these security protocols are energy efficient by using block ciphers?
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### CA certificate expired on openvpn [migrated]

I have a problem with CA certificate on openvpn, it has expired and clients cannot connect. I tried to create a new certificate with the ca.key, but it did not work. Here is the command I used to ...
24 views

### OpenSSL ECDH key exchange 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 ...
33 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 ...
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### Starting point on Fully Homomorphic Encryption and Proxy Re-encryption [on hold]

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.
23 views

### Deriving message from signature (RSA) [duplicate]

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 ...
339 views

### 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 ?
21 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 ...
102 views

### What is the state of cryptographic obfuscation in 2015?

Cryptographic Obfuscation is a technique that allows one to obfuscate source code in a secure way (as opposed to insecurely mangling it into spaghetti code.) For example, here is a way to protect a ...
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### 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 ...
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### 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 ...
55 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 ...
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### Test for randomness - randtests - fails [migrated]

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 correctness of the PRNG. For ...
146 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 ...
31 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 ...
62 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 ...
24 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 ...
61 views

### What are the differences between curve NIST P-521 and Edwards E-521 for signature?

I implemented and used the P-521 curve for ECDSA. Signatures are 132 bytes long. It seems that Edwards E-521 is safer but I did not investigated very deeper. What is its signature length ? How is it ...
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### End-to-End (Point-to-Point?) Email encryption [migrated]

I'm looking into providing security for the email server I recently deployed, however the subject matter is a touch more complex than I anticipated and I would appreciate confirmation or correction of ...