# All Questions

1answer
74 views

### SAT as a basis for a PKCS - Effective? [closed]

I recently read this paper on a public key cryptosystem based on the SAT-problem.(SAT=boolean satisfiability problem, NP-complete) The speed of this system looks quite promising as extreme ...
3answers
121 views

### Is what i'm trying to do safe?

What both parties have: Server Master Secret (MS) Server supported versions (Svers) Agreed upon version (ver) Client Master Secret (MS) Client supported versions (Cvers) Agreed upon version (Ver) ...
1answer
59 views

### AES process candidates implementations and usages

There were fifteen candidates in the AES selection and I suppose that Rijndael wasn't the single good algorithm. I know that Camellia is an evolution of E2 candidate and can be used as symetric ...
1answer
30 views

### CCA secure or not?

Let $F : \{0,1\}^n \times \{0,1\}^n \rightarrow \{0,1\}^n$ be a PRF. And let the encryption function be $Enc{_k}(m) = r || (F{_k}(m) \bigoplus r \bigoplus 0^n)$ , where r's value is random. Is this ...
2answers
58 views

### Fortuna: why are source ID and data length added together with entropy data into the pools

Section 9.5.6 of Cryptography Engineering states that The concatenation [of source number, length of data, and data itself] is then appended to the pool. Why are we including source number and ...
2answers
68 views

### Negilible Function $\frac{1}{n!}$

Is $\frac{1}{n!}$ a negligible function where $n$ is a security parameter? Application: I have a vector of n>100 elements. I permute it and give it to an adversary. The adversary can break it if it ...
0answers
101 views

### Is Information Loss in Crystalline Cipher a Good Approach to Anti-Cryptanalysis? [closed]

Crystalline Cipher is a new cipher released under the MIT license. The approach employed manipulates the locations of bits and bytes to effectively scramble the plaintext, erase information from ...
1answer
111 views

### Generate a list of valid ASCII codes

I have read many pages about encryption but I am really stuck on this. For access control to a building I want to print a 10 character ASCII code on a ticket (as a barcode). The barcode reader ...
1answer
58 views

### Authenticate a short message with redundant encryption instead of using a MAC?

I have a short message that’s exactly 128 bits of length. The message serves as a time-limited authorization token for a database. It contains a permission profile ID (64 bits) and an issue timestamp ...
0answers
23 views

### Proposed unidirectional authentication scheme

I've been looking around for a way to authenticate a client to the server and deliver a message, but in a unidirectional fashion - that is, the client sends messages to the server, but the server ...
2answers
60 views

### Modifying a [CRC32] checksum protected file [closed]

I dont want to ask for help without showing how far I came by myself, so this is what I have so far: The file of interest is an encrypted/obfuscated .bin script, which cotains information on certain ...
1answer
40 views

### Why perfect secrecy can be ensured when a plain message and a cipher-text based on one-time pad are correlated?

First, some well-known results are as follows. For random variables $X$ and $Y$, we have $$H(X,Y) \leq H(X) + H(Y).$$ The equality is achieved when $X$ and $Y$ are independent. Second, in one-time ...
1answer
38 views

### Does the plaintext have to be at least as long as the key in Polyalphabetic substituion cipher

In polyalphabetic substitution cipher, if we have a key $k$ (a string of letters) of length $n$ does the plaintext $m$ (also a string of letters) have to satisfy $|m| \geq n$? Also, side question, ...
1answer
39 views

### what is legend of h(r) in this protocol?

can you help me what is legend of h(r) in below protocol? ‎‎$A‎\leftarrow‎{B}\quad:{h(r)‎‎}{,B}{,P{_A(r,B)}}‎\\A‎\rightarrow‎{B}\quad:r$
2answers
142 views

### Practical Uses for Timing Attacks on Hash Comparisons (e.g. MD5)?

Consider the following code snippet: ...
3answers
2k views

### A timestamping authority (digital notary)

Does there currently exist a free online service that accepts a file, hashes it, takes an authoritatively chosen timestamp (from one or more time services), signs these and sends this signed message ...
0answers
31 views

### How to implement H1(x) [closed]

I want to implement H1(M,S1) in python for my project.Where , H1 :{0,1}* × Zp->Zq. M is the message and s1 is the key.
1answer
106 views

### Inserting a backdoor into a cryptographic hash function

I'm curious as to how a backdoor can be built into a hash function. What might it take the form of? What's probability of getting one that can be backdoored in a way that can actually undermine its ...
0answers
22 views

### How can one improve Rijndael's with more efficient SBoxes?

Knowing that the Rijndael's SBox is a pre-calculation from a composition of two operations (an inversion in a polynomial field, and an affine transformation that can be saw as a product and an ...
1answer
17 views

### Ephemeral Diffie-Hellman in a symmetric crypto context

I'd like forward secrecy in a case where the two sides have a shared long-term symmetric key. I intend to use AES in GCM. It looks like ephemeral Diffie-Hellman is the best way to generate the session ...
2answers
32 views

### what is recommended x length in Diffie Hellman algorithm

According to rfc documents http://tools.ietf.org/html/rfc2412#appendix-E.2 & http://tools.ietf.org/html/rfc3526#section-3, it has defined the prime and the ...
0answers
12 views

### AES GCM Mode Client Side [closed]

I am implementing browser side cryptography in my project. I want to implement the AES-GCM in both client side and server side. I am using nodejs for that. I have researched on the net but I found ...
1answer
60 views

### How do we guarantee plaintext is coprime in RSA?

The specifications for RSA state: $P^{\phi(N)} \equiv 1 ~mod~N$ if and only if $P$ and $N$ are coprime. Here $P$ is the plaintext and $N$ is the product of two suitable primes $x_1, x_2$. My question ...
0answers
44 views

### Calculating XOR Key Sizes

I've been playing around with the Matasano crypto challenges (cryptopals.com). I had a couple false-starts on the challenge that has you creating a program to calculate the key size of a XOR encrypted ...
1answer
1k views

### Duration for attacking Two-Key Triple-DES Encryption using all RAM ever built?

I am considering attacks on Two-Key Triple-DES Encryption assuming $2^{32}$ known plaintext/ciphertext pairs (that's a mere 32MiB of ciphertext) by the method devised by Paul C. van Oorschot and ...
1answer
91 views

Apologies for the obviously ridiculous question but I need to know where I'm going wrong here. For RSA, we compute $n=pq$ for primes $p$ and $q$. We then choose an $e$ such that $gcd(e, ... 1answer 48 views ### Value of S and r in Fiat-Shamir Protocol In the book Cryptography and Network Security by Forouzan,in chapter 14, Fiat-Shamir protocol, its mentioned that two large prime numbers p and q are chosen and kept secret. However n=p*q is made ... 1answer 51 views ### How to exchange authentication keys I am trying to create a secure Bluetooth Low Energy connection. The peripheral server (the main device other people would connect to) would need to service many clients (users) and due to hardware ... 2answers 1k views ### ASCII to same-length ASCII encryption? I need to encrypt an ASCII string [a-zA-Z0-9:] to an ASCII [a-zA-Z0-9] string of the same length. It doesn't have to be unbreakable, it's sufficient that it won't be readable at the first sight. The ... 0answers 19 views ### System of linear congruence, not relatively prime [migrated] Consider we have the following set of congruences $$x\equiv b_i \pmod {m_i}$$ for all$1\leq i\leq d$.$m_i$'s doesn't have to be relatively prime, so the Chinese remainder theorem doesn't work here. ... 0answers 32 views ### We are trying to decode a mysterious website, need help from experts [closed] Here is the link of our investigation - http://www.reddit.com/r/gateway71 We are currently stuck on gif with blinking boxes and voice that appears to say the same what is happening on the gif. Here ... 2answers 131 views ### General questions about cryptography for password security [closed] I'm pretty new to this and find it quite interesting, but my brain won't process how it works so I have to ask some questions :) Why is cryptography used? Is it for extra security once the password ... 1answer 73 views ### Why cant Public Key Encryption be perfectly secure? [duplicate] I would be very grateful for any help. I cant figure out why (probabilistic) public key encryption schemes can never provide perfect secrecy? Any Ideas? Excerpt: In contrast to the private-key ... 0answers 16 views ### How to get the (x,y) from the EC point in the pubkey of an ECDSA certificate? I have this certificate, and I have the bitstring of the pubkey that should represent Q = (x,y) = [d]P. How can I get the x part? (The curve is the NIST B-163) 0answers 21 views ### How to convert PGP clearsign into the ascii armored OpenPGP message? [closed] What I do have is the output of echo 'Test' | gpg --clearsign (take a look at below for instance): -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Test -----BEGIN ... 0answers 28 views ### Recovering key length from transposition block cipher ciphertext First of all I would like to say hello to all StackExchange users. So far I've been stalking the forum for some time, now it's time to leave the shadows. In my master thesis I'm writing about ... 0answers 22 views ### The Massey-Omura Cryptosystem (1983) [closed] disadvantages and advantages of The Massey-Omura Cryptosystem (1983) 0answers 16 views ### What text provides the best chronological/historical overview of Crypto [closed] I am interested in learning more about the history of cryptography - any recommendations on books? Thanks in advance! 0answers 35 views ### What's your favourite privacy tool? [closed] we're currently working a community project that provides knowledge and tools to protect your privacy against global mass surveillance. Since the project is driven on user suggestions I came here to ... 0answers 29 views ### Outsourced Multiparty computation proof in Ideal world I need to know in an outsourced two party computation where honst$A$and$B$outsource their private and secure data to a malicious server, why we need to design a simulator that interacts with an ... 0answers 14 views ### Protocol for signing and timestamping documents for e-archive system [migrated] we are building system for storing PDF file for long term in database. Before we store PDF file in database we have to: ... 1answer 40 views ### Is there a tangible benefit in keeping the number of PBKDF iterations secret and not storing them with the ciphertext? Suppose I have a local file and it is encrypted with a symmetric key derived from a strong passphrase, unique salt and$x$number of PBKDF (e.g. Scrypt) iterations. I am interested in keeping this ... 1answer 28 views ### Durability of the crypto container and there old copies / backups [closed] Do durability of the crypto container decrease if I will store near that old copies of this container / backups? If yes, how much it falls? I feel that when I do backups it reduce resistance of ... 1answer 79 views ### what is the public information in Elliptic curve cryptosystems [on hold] Currently my knowledge about Elliptic curve is quite limited to the textbook and I don't know how a practical Elliptic curve cryptosystem works. I read an example about key exchange using Elliptic ... 2answers 84 views ### DH with AES - is that an acceptable security scheme over UPnP? I'm trying to devise a good security scheme to protect comms over Wi-Fi. Right now, I have 2 devices that already communicate via UPnP but I need to secure this communication. I've come up with this: ... 1answer 111 views ### Is HMAC-MD5 still secure for commitment or other common uses? MD5 collisions have been out for some time. In spite of this, HMAC-MD5 is still secure for authenticating data1. This illustrates a strength of the HMAC construction, it does not require that the hash ... 0answers 33 views ### Random number generator design [closed] How do you design a random number generator using 8051 that displays a random number between 0 & 99 in detail? 1answer 57 views ### where should private and public keys be stored? [closed] I am kind of confused whether should a newly generated key pair be stored in a keystore or in just a normal plain text file? From what I read from online source, there are serveral explainations ... 0answers 46 views ### SHA3 Keccak, absorbing data to the state I'm working on implementation of keccak algorithm and have one problem. Tell me please, takeing an example "test": will state (before block permutations, but after padding - pad10*1) look like this: ... 1answer 39 views ### Second generator for secp256k1 curve I want to get a group element$h$on the elliptic curve secp256k1. The important thing is that no one should know the discrete logarithm of$h$with respect to$g$. That is,$h\$ should be created from ...

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