2
votes
1answer
77 views

Number of keys when using symmetric and asymmetric encryption?

Quoting part of my homework/assignment: How many keys are required for secure communication among 1000 person if: Symmetric key encryption algorithm is used? Asymmetric key encryption ...
2
votes
1answer
150 views

Can XEX or XTS modes be used with only one tweak?

XEX Mode (with two tweaks) is the following scheme: $X = E_{k}(I) \otimes \alpha^j \\ C = E_{K}(P \oplus X) \oplus X$ where $I$ and $j$ are both tweaks (sector number and block number respectively). ...
2
votes
1answer
80 views

Simplified Key Wrapping to Achieve Only Confidentiality?

I'm looking for help in understanding why the algorithm described here would not deliver adequate protection of confidentiality. We don't care about other criteria such as authenticity or integrity. ...
2
votes
1answer
129 views

ECC Complexity order of point addition, scalar point multiplication and selecting random point

I am facing this problem in calculating the order of a process which involves ECC point addition: $P+Q$ , scalar multiplication: $aP$, and selecting random points in the group. The group is of prime ...
2
votes
1answer
86 views

Frequency analysis of transposition ciphers

Can we do frequency analysis of transposition ciphers? If yes, please tell me the procedure and I would be happy if you provide me with some links related to it. I heard that it can be done using ...
2
votes
1answer
95 views

Is it possible to track down copies of WW2-era codebooks?

I've got an academic curiosity regarding some of the old Japanese naval codes used during World War II specifically… but I was just wondering if any of the codebooks from this era had been made ...
2
votes
1answer
79 views

Generating shared secret random permutation

There are three blind card game players. Each player does not trust any other, even prejudicing other two players may not be blind, or there may be others in the room, peeking at their cards. In ...
2
votes
1answer
73 views

Encryption mode with chained algorithms

Suppose that I want to encrypt some data using two different algorithm chained (e.g. AES and Serpent) and harnessing the benefits of CBC. I can do: ...
2
votes
1answer
124 views

Questions about hash functions

Let $H$ be a secure hash function (e.g. SHA256), is it possibile to find $H(M1)$ given $H(M1||M2)$ if the length of $M1$ and/or $M2$ is exact the block size of the hash (that is, 64 bytes for SHA ...
2
votes
3answers
193 views

Is it overkill to run a key generated by OpenSSL through pbkdf2?

I'm generating a key & iv with OpenSSL via: ...
2
votes
1answer
138 views

Fast modular reduction

I am looking at ways to speed up modular reduction for the polynomial $$2^{256}-2^{32}-2^9-2^8-2^7-2^6-2^4-1$$ I have read the paper "Generalized Mersenne numbers" by J.A. Solinas, but it does not ...
2
votes
1answer
112 views

Detecting steganography in the stream of short messages

I have stream of millions of short n-bit (n<30) messages generated by some random number generator. The source of random number generator is not available to me. I suspect there are messages used ...
2
votes
1answer
121 views

Is ed25519 a “hash signature”

Writing my last question, I saw the hash-signature tag. I tried to research it best I could, but I'm simply overwhelmed in this field. I don't think it means to simply hash data before signing, but ...
2
votes
1answer
151 views

Is it possible to tweak AES-GCM so that it is satisfactory for whole-disk encryption (like XTS mode)?

Is it possible to leverage a preexisting implementation of AES-GCM to provide the key security benefits essential for full-disk encryption (similar to AES-XTS)? GCM is a popular encryption mode ...
2
votes
1answer
94 views

Secrete message sharing using N private keys

I'm looking for an encryption scheme that could possibly meet the following requirements. Let, $X = plaintext$ $M = (pub, priv)$, where $priv == (Ky + Kz)$ Given ...
2
votes
2answers
163 views

RSA: What happens to restrictions of plaintext n, dependent on p and q?

Ok - i will try to ask my question as clear as possible. Im getting a little deeper into the RSA-cryptosystem. At one point i'm a little confused. We have a plaintext $x$ and ciphertext $y$, with $x ...
2
votes
2answers
85 views

Should tweak be unique per message?

Since tweaks are like IV,Salt for block cipher inputs . Should they be unique for each message ? If they are to be unique per message then what is the advantage of giving tweak directly into the ...
2
votes
1answer
83 views

Do both client and server need to implement OpenSSL protections to protect from CBC attacks

In regards to the protections implemented in OpenSSL 0.9.6d (described in section 2. http://www.openssl.org/~bodo/tls-cbc.txt). My understanding is that the mechanism prepends an empty record when ...
2
votes
1answer
73 views

Can you explain the counter in the Key derivation function of PACE?

I try to understand the PACE-Protocol, especially the Key Derivation Function in ECDH on page 33. Can someone explain me, what the Counter is good for? Often there are iteration counters in KDF - but ...
2
votes
1answer
90 views

2PC Private Set Intersection Optimized for asymmetrically sized sets

I am researching some concepts of practical 2 party computation and was curious if anyone could point me to a research paper that is focused on private set intersection where one party has a very ...
2
votes
1answer
103 views

Would data be secure if a cryptographically secure PRNG was used for encryption?

For example, say you have a client and server. You use asymmetric encryption to securely deliver two seeds from server to client. Each user then seeds two PRNGs (one for incoming data, one for ...
2
votes
2answers
224 views

How can A pass a message to B, while preventing a third party from sniffing infos?

$A$ has a message that he wants to send to $B$, without a third party being able to learn the contents of the original message. $A$ encrypts the message and sends it to a server. The server decrypts ...
2
votes
1answer
97 views

Cryptographic Arithmetic Toolbox/Software [closed]

This term I have many cryptography courses treating finite fields. I was wondering if there is any good software that could help doing basic operations in galois fields etc. I already googled but ...
2
votes
1answer
90 views

A confusion about HMQV?

As the full version of HMQV is very long, I will give a graph of it below \begin{array}{@{}l@{}c@{}l@{}} \hat{A} && \hat{B} \\ (a,A=g^a)&&(b,B=g^b) \\ x\in_R[1,q-1],\quad X=g^x ...
2
votes
1answer
170 views

Off-the-record communication

Is my protocol correct? For fun, I tried to design a protocol that would allow off-the-record communication. I'm not sure it works, I have a feeling there might be a problem with it that I'm not ...
2
votes
1answer
97 views

How is a PRNG used in the PGP?

I'm currently reading up on the components of PGP and I am wondering what exactly the PRNG is used for. PGP uses ANSI X9.17 and entropy from a users keystrokes to generate a temporary key. So, is ...
2
votes
1answer
125 views

Need 32-bit mixing function that has perfect avalanche between octets

for my hobby tinkering project, I need a mixing function that takes 32-bit input and has 32-bit output (and will, most likely, run in a 32-bit C environment) and the following property (independent of ...
2
votes
1answer
125 views

Reusing PGP key when generating SSL Certificate Authority?

Does it make sense to reuse some of the keys from my PGP (gnupg, gpg) keyblock when generating my own SSL Certificate Authority (a toy one for myself and a few web services of mine)? In an ideal ...
2
votes
1answer
106 views

Upper bound Linear Feedback Shift Register

It is clear that when we have any output stream $x_0,x_1,...$ produced by linear feedback shift register than this output has to be periodic. Now I was wondering if we can find an upper bound for ...
2
votes
1answer
197 views

Is this new server API authentication protocol secure?

I need a secure protocol to authenticate client side users with my server which has an API. I am devising something more secure particularly to resist active MITM attacks where an attacker may modify ...
2
votes
2answers
1k views

How to obtain KCV from the key

Simple question: we have AES 128 encryption and a key. How can we calculate the key check value (KCV)? One example: key is 48C3B4286FF421A4A328E68AD9E542A4 and KCV should be 77DC84. I am trying it ...
2
votes
1answer
108 views

Authentication of machine before installation (to stop piracy) [closed]

I have a web-software project which needs a bit of protection in form of authencitation… This web based software runs on an intranet. There is no access to the internet from these terminal machines. ...
2
votes
1answer
118 views

Decryption or attacking DES encrypted file

I have a file that has been encrypted using DES and am looking to decrypt and find a secret message encoded. All I have is the file which is full of binary data. There is no key or anything else which ...
2
votes
1answer
66 views

How to pass an arbitrary signature to a certificate

I am trying to sign certificate (X509) using secret sharing. That is shareholders combine their signatures to produce the final signature which will be in this case the signed certificate. However ...
2
votes
1answer
205 views

Question about CBC-MAC

I found this question from a textbook but I don't really understand what it is asking: Suppose $c$ is $1$ block long, $a$ and $b$ are strings that are a multiple of the block length, and ...
2
votes
2answers
121 views

Can you give me an example of any PKC encrytion algorithm with coins?

I'm reading a Definition of Public Key Encryption and here say: ... Enc is a (possibly) probabilistic polynomial time encryption algorithm which takes as input a public key $pk$, a $m\in M$ and ...
2
votes
1answer
141 views

Feasibility of using a base 26 LFSR for cryptography by hand

I have been playing with base 26 LFSRs (i.e. using the alphabet) and noticed that the XOR operation for base 26 is just the tabula recta and so can be done very quickly. This made me wonder whether a ...
2
votes
1answer
134 views

Why does Merkle's Puzzle requires Eve quadratic complexity of effort to break the system?

The way Applied cryptography 2ED explains the puzzle is as follows (I paraphrase it): Bob generates 2^20 messages of the form x,y where ...
2
votes
1answer
191 views

In RSA, what is faster attacking “d” when plaintext is known, or factoring when M is unknown?

I'm aware of two methods to attack RSA: Brute force factoring, where no plain text is available Brute force (1/e) mod φ where the plain text is available as described here Question Given an ...
2
votes
1answer
45 views

How can I evaluate the congruency of an AKS primality test?

Despite the fact primality test is a mathematical issue, it plays a part on the security of many cryptosystems such as RSA. I was trying to understand how it works until I came to the following ...
2
votes
1answer
548 views

DES Key Schedule Algorithm

Reading through the DES Specification it says that the keys are permuted with PC-1 initially and then shifted left both $C$ and $D$. However, before it gets ...
2
votes
1answer
238 views

Is SHA-256 a one way permutation when restricting the domain to {0,1}^256? [duplicate]

Suppose we consider the space of $\lbrace 0,1 \rbrace^{256}$ as the domain and SHA-256 as our hash function. Does SHA-256 become a one way permutation? Has anyone tried to prove this? Or can it be ...
2
votes
1answer
184 views

2 comparable hashes generated from one string

Assume a website where people log in with their password. The password is now stored in sql database as: md5(password + random_salt) We are adding the ...
2
votes
1answer
136 views

The Goldreich-Goldwasser-Micali Construction with bad PRGS

I understand that if we have a secure PRG then the Goldreich-Goldwasser-Micali construction gives us a secure PRF. However, what I've not been able to find much material on is how will the GGM ...
2
votes
1answer
220 views

Verifying Self-signed SSL Client Certificates

I have a service and I want to authenticate my clients using SSL client certificates. Now I want the key exchange process to be as simple as possible, kind of like SSH: You generate a keypair and ...
2
votes
1answer
58 views

How are the lower levels calculated using upper levels in an optimized Merkel Hash Tree?

I was reading about the TIK protocol for thwarting wormhole attacks on adhoc networks. It uses a Merkel Hash Tree to store keys. But since the number of keys can be large, the tree is optimized by ...
2
votes
1answer
214 views

some of my confusions about DDH assumption

The wiki defines the decisional Diffie–Hellman assumption as follows: Decisional Diffie–Hellman assumption Consider a (multiplicative) cyclic group $G$ of order $q$, and with generator $g$. The DDH ...
2
votes
2answers
156 views

Privately Sum Values without Dealers, MPC

Suppose $n$ actors each hold a plaintext $p_i$. We wish to find $\sum p_i$, without leaking any information about individual $p_i$. Any actor (or any link in the network) could be controlled by an ...
2
votes
1answer
128 views

Can you help me understand PFS and wPFS?

Every time I encounter the concepts of PFS (perfect forward secrecy) and wPFS (weak perfect forward secrecy), I feel uncertain about them. My understanding is that: PFS ensures that, if the ...
2
votes
2answers
149 views

Security of S/MIME in case of CA compromise

Suppose Alice and Bob are exchanging messages using S/MIME, protected by certificates that have been issued by either the same CA or by two mutually independent CAs. There exists an adversary Mallory ...

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