2
votes
1answer
308 views

Is base64 the best two-way hash function to encrypt and trasmit a set of integer numbers via Internet?

I am writing a mobile game and I need to save my game data on my game server, So crackers can not find and access the saved files(data) on their mobile, the game data can be expressed by numbers, So, ...
3
votes
1answer
87 views

Implementing 5 modes of operation with a hash function

Is it possible to implement any of the 5 modes of operation (ECB, CBC, OFB, CFB, CTR) with a hash function?
2
votes
1answer
162 views

CPA and pseudorandom generator

Just started learning about Cryptography and Network Security in general, and I can't seem to grasp the understanding of the following question. Please correct me if I am misunderstanding anything. ...
3
votes
1answer
53 views

Attacks on WinRAR volumes reusing same password?

I have quite a few WinRAR volumes that are all encrypted with the same password. The password is long and unbruteforceable, but I recently read that WinRAR uses PBDKF2 as its key-derivation function ...
2
votes
1answer
83 views

Is it secure to use order preserving encryption in practice?

When I read papers, I often see the comments, "order-preserving encryption is deterministic and it is not IND-CPA secure", or in general "it is not secure enough to be implemented in practice". So I ...
2
votes
0answers
113 views

Limit the number of private key uses for RSASSA-PKCS1-v1_5 with SHA-256 signature?

Assuming all messages and their signatures are available to the attacker, is it secure to use the same RSA private key to sign many messages (roughly $10^{6}$) via PKCS#11 ...
7
votes
3answers
297 views

What was the first MD5 collision ever constructed?

We all know that MD5's collision resistance is severly broken. But when thinking of "random" strings with great cryptographic importance I've come up with NIST's curve seeds and MD5 collisions. But ...
1
vote
0answers
41 views

Symmetric stream cipher, is it known?

I am thinking on a simple symmetric stream cipher. My first idea is the following: The key is a set of array of random bytes ($\underline{k}_1$ ... $\underline{k}_n$), whose length is $l_1$, $l_2$, ....
4
votes
1answer
115 views

Signing and verifying message consisting of several parts

Given a message $m$ that consists of several parts. we want to be able to verify individual parts or a combination thereof. The simplest solution is independently signing each part. But since ...
2
votes
1answer
64 views

Modified version of a CPA-secure encryption scheme

The following encryption scheme: choose a random string $r \leftarrow \{0,1\}^n$ and compute the ciphertext $c= \thinspace <c_0, c_1>= \thinspace <r, F_k(r) \oplus m>$, assuming $F$ a PRF; ...
5
votes
2answers
73 views

Does $(u_1=r_1\cdot x,\ \ w_1=r_1\cdot z, \ \ u_2=r_2\cdot x,\ \ w_2=r_2\cdot z)$ Leak Information?

Consider we have a fixed value $x$. We pick values $ r_1,r_2,z\leftarrow \mathbb{F}_p$, where $p$ is a large prime number, and it is public. So $r_1,r_2,z$ are uniformly random values. We compute ...
4
votes
2answers
47 views

Does SRP also authenticate the server to the client?

The Secure Remote Password (SRP) protocol lets a client prove to a server that it knows a specific password without revealing that password to the server. The server stores a cryptographic verifier ...
1
vote
1answer
46 views

In bilinear pairings, is it possible to let someone be only able to decrypt ciphertexts in $G_1$ but not able to decrypt the ciphertexts in $G$?

For example, in Don Boneh et al.'s paper "Evaluating 2-DNF Formulas on Ciphertexts", they gave an encryption system that the cihpertext can be in either $G$ (when only additional homomorphic ...
2
votes
1answer
217 views

Obtain 384 bits from a 256bit MasterSecret

I'm currently implementing, with crypto++, and AES tranmsission system, whose key is based on a previous ...
2
votes
0answers
94 views

Is there a way to slow down collision attacks using iteration?

The simple way to iterate a hash function $H(H(m))$ only makes brute force preimage finding slower, but leaves collision attacks as fast since a collision in the inner hash function is a collision in ...
4
votes
2answers
856 views

Is it secure to concatenate two 16-bit random numbers into a 32-bit one?

I'm working on a security application for RF modules aimed to protect a communication between an autarkic sensor and a line-powered receiver against MITM (man-in-the-middle attacks). I decided to use ...
0
votes
1answer
70 views

What is the meaning of the overlapping region on OTP-perfect secrecy diagram?

I'm new to cryptography. I want to ask about OTP-perfect secrecy diagram like figure below: On the overlapping region (middle), notated by R(X;Y;Z). R can be calculated by I(X;Y) - I(X;Y|Z). ...
2
votes
1answer
56 views

Encryption on the cloud with versioning

Can file-versioning, which is available for instance in Dropdox, weaken the security of encrypted files if someone is able to see two or more snapshots of the ciphertext at different times? To be ...
1
vote
1answer
109 views

Double Encryption Using same key

I am new to crypto and wondered what would happen when we encrypt twice using any algorithm and the same key. Consider two block ciphers A and B. We generate the ciphertext as c = A(B(m)) for any ...
1
vote
2answers
219 views

FIPS 140-2 Compliance Testing

Is there any tool which can be used to test that implementations follow FIPS 140-2 Compliance ?
1
vote
0answers
32 views

Where can I find a versatile PKI and library leveraging curve25519?

I note that Things that use Curve25519 provides a long list of protocols, software, and libraries that leverage curve25519, but I'm wondering if there is any such software that more fully implements a ...
1
vote
2answers
227 views

What are the practical limitations of Asymmetric encryption vs Symmetric encryption? [duplicate]

I hear it commonly said that the advantages of Symmetric encryption are speed and no limit to the amount of data that can be symmetrically encrypted. I also hear it commonly said that the advantages ...
2
votes
1answer
67 views

Subkey generation in OMAC1/CMAC with XTEA?

All implementations of CMAC that I have found so far use a block cipher with the same key and block size. However, XTEA enciphers a 64 bit block by using a 128 bit key. If ...
5
votes
2answers
207 views

Picking a nonce in the context of CCM (CTR with CBC-MAC) mode

After having read the RFC 3610: Counter with CBC-MAC (CCM) and the Wikipedia article on CTR mode, I'm not sure how a nonce should be picked. The RFC says: A nonce N of 15-L octets. Within the ...
4
votes
1answer
53 views

apprSVP in lattices

The approximate Shortest Vector Problem (apprSVP) is a problem where, given the basis and the approximation factor $\gamma$ (a function of the dimension $n$), one must find a vector $v$ belonging to ...
0
votes
1answer
100 views

Explain same encryption time for two files of different sizes

I am encrypting files in a two layered fashion as follows: Inner layer is 128 bit AES-CTR encryption Outer/Second layer is a simple one time padding with a particular key. While testing the ...
0
votes
1answer
57 views

ciphertext packing for bandwidth optimization

Lets say $Alice$ needs to send ciphertext $c_b = enc(m_b,k_b)$ to $Bob$ and ciphertext $c_c = enc(m_c,k_c)$ to $Carol$, for both the ciphertexts notice that underlying plaintexts are different (i.e. $...
1
vote
1answer
140 views

How to prove that the Permutation cipher is not CPA secure?

Encryption scheme is called a permutation cipher if every plaintext string with letters $a_1,\ldots, a_n$ is encrypted as $a_{\pi(1)}, \ldots, a_{\pi(n)}$ for some (not necessarily uniform) ...
5
votes
1answer
538 views

How to generate unique (random) numbers that can be traced back to a unique source number?

I need to generate unique (random) numbers that I can trace back to a unique source number. For example: source number A can generate numbers A1, A1, A3 .... Am source number B can generate numbers ...
3
votes
1answer
156 views

Paillier Cryptosystem - Practical applications?

I wonder: are there any real-world practical applications using the Paillier cryptosystem , as introduced in [1], or some derivations of it? I'm aware of quite a few schemes proposed in literature ...
3
votes
1answer
130 views

Is this a proper PBKDF2 key derivation function algorithm?

I've started implementing PBKDF2 algorithm recently and since I'm new in crypto, I would like to ask if my implementation is good. I looked up some documentations and I tried to follow many of them ...
5
votes
1answer
65 views

Comparing two definitions of one-way function

I'm reading Rafael Pass's lecture notes on one-way function and came across two definitions. The first one is: A function $f$ is one-way if $f$ can be computed in P.P.T. and there exists no non-...
1
vote
1answer
218 views

Determining if a ciphertext can be decrypted

I want to know what the state of the art in the following cryptographic problem is. Assume a public channel on which encrypted messages are exchanged, using symmetric key encryption. I hold a couple ...
5
votes
1answer
172 views

Is EncFS good for online storage services?

Conclusion from an EncFS audit: EncFS is probably safe as long as the adversary only gets one copy of the ciphertext and nothing more. EncFS is not safe if the adversary has the ...
0
votes
0answers
16 views

In the RSA encryption system, are there not multiple messages m that give the same cipher text c? [duplicate]

For example: p = 5, q = 11, n = 55 $\phi$(55) = 40 e = 3, $\phi$(55) and 3 are relatively prime m = 3, then: $3^3 mod(55) = 27$ m = 113, then: $113^3 mod(55) = 27$ I heard that e and $\phi$(n) ...
2
votes
1answer
309 views

XTEA: patterns in plain text

I'm using XTEA to encrypt passwords that I store in a database. (I need to be able to decrypt these passwords later to log in on another system.) But now I have noticed something: if I decrypt a ...
4
votes
0answers
61 views

Are there any test vectors for the CMS content type AuthEnvelopedData (for AES-GCM)?

I am looking for CMS AuthEnvelopedData test vectors for AES-GCM mode. I haven’t seen any ready-to-use test vectors for it. There are test vectors for AES-GCM mode but not for its CMS support. I even ...
5
votes
2answers
289 views

When is the Random Oracle model (not) necessary?

Hash functions are often used in cryptographic schemes and protocols, and that doesn't necessarily mean that their proofs are on the Random Oracle model. That leads to the following question: What is ...
4
votes
1answer
163 views

Effect of ESSIV when used with XTS

I looked everywhere on the web and I did find a lot of information about full disk encryption, but nothing really answered my question. When formatting a partition to use LUKS, the two most common ...
4
votes
1answer
102 views

Distribution based integer factorization

The past week I've been looking into - and playing with - algorithms for factoring RSA moduli. From what I understand, it's important that the primes p and q are of the same magnitude as the square ...
2
votes
1answer
77 views

A secure function evaluation problem and an alternative of 1 out of n oblivious transfer?

I am considering a "secure function evaluation" problem: Consider two parties: A and B. A has a one-to-one mapping function $f(x)=k$. Basically, the function $f(x)$ can be regarded as a table of two ...
2
votes
0answers
66 views

Detecting steganography by analysing non-significant data entropy?

I am not thinking only steganography in images, I think it is also possible to encode data for example into the length of spaces of a clear html text. I suspect, the steganography changes (elevates) ...
2
votes
1answer
35 views

Leakage in Secure Two party Computation

Am trying to understand Garbled Circuit based approach for Secure Two party Computation. There isn't much leakage in the classic millionaire's problem where the comparison circuit is used. But ...
1
vote
1answer
663 views

Precisely how does CBC mode use the initialization vector? [duplicate]

As I understand it, AES in CBC mode does an XOR of the 128-bit initialization vector and the first 128 bits of plain text. Is this correct? I am using the PHP 5.3 openssl extension in aes-256-cbc ...
6
votes
3answers
200 views

Is there an upper bound to the private exponent in RSA?

In the RSA algorithm, we choose $p$ and $q$ as prime numbers and we select a value $e$ which is coprime to $\varphi(pq)=(p-1)(q-1)$. Then we calculate $d:=e^{-1}\bmod\varphi(pq)$. My question is: ...
6
votes
2answers
82 views

How to propagate error in variable-sized message?

I want to design a scheme to encrypt a variable-length message with a secret key, to provide confidentiality. The message is a short human-readable text string with byte granularity, let's say under ...
1
vote
1answer
181 views

How to determine the RSA Private key size from the Public.key file?

Question: How to determine the RSA Private key size from the Public.key file? Just roughly, how big it could be? ...
3
votes
3answers
101 views

Authenticate ephemeral key exchange

At the moment I'm designing a crytosystem for a VPN server. One of the requirements is Perfect Forward Secrecy, but I'n not sure how to implement authentication on the ephemeral key exchange. If both ...
1
vote
1answer
44 views

Security of a signature scheme based on both factoring and discrete logarithms

I have seen this paper: A New Signature Scheme Based on Multiple Hard Number Theoretic Problems by Ismail and Tahat: In this paper, we propose a new signature scheme based on two hard number ...
6
votes
1answer
227 views

How is OID 2a 86 48 86 f7 0d parsed as 1.2.840.113549?

I saw that an RSA key, created by OpenSSL, contains the following HEX string: 2a 86 48 86 f7 0d 01 01 01 that HEX string gets interpreted as Object ID: 1.2.840.113549.1.1.1 It is obvious ...

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