2
votes
1answer
222 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
95 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
871 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
72 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
57 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
112 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
274 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
34 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
240 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
77 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
226 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
56 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
101 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
60 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
142 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
553 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
159 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
154 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
233 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
194 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
18 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
333 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
63 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
294 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
208 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
104 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
85 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) ...
3
votes
1answer
40 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
753 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
201 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
204 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
112 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
45 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
238 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 ...
1
vote
2answers
336 views

Basic Encryption and Decryption related question

I recently started studying cryptography and got interested in the subject. But I got this doubt when I was studying the encryption scheme. Even though we encrypt our message and change it into ...
0
votes
1answer
73 views

What are the first 4 and last 2 bytes in DH parameter files?

when we generate DH parameters file in PEM format, like this: ...
3
votes
2answers
69 views

Hiding identifying data while allowing matching?

I do research with people about their illegal drug use, and for one project I'm doing surveys with them when they visit a needle exchange. So over time the same people get repeatedly surveyed as they ...
1
vote
0answers
22 views

Is there a system where I can securely store a secret value and compare a semi-ambiguous input to it?

I have an idea for a new kind of mobile phone lock screen. When you first create your pattern, you put together a series of colors and compass directions from the following choices: Red, Blue, Yellow, ...
3
votes
1answer
226 views

Encrypt with one cipher and decrypt with a different cipher?

I recently installed an android app called Secret Space Encryptor and think I found a serious flaw in it. Let me explain: This app provides a variety of different ciphers to use and I used Threefish ...
0
votes
1answer
25 views

Lower defree annihilator of function

Suppose $f=x_0x_2(x_1+1)+x_1x_3(x_0+1)$, annihilator is such function $g$, so that $gf=0$ for all $x$ Intuitively solution(for some reason) is obvious - $g=x_0x_1$, which holds true. (Cloud sagemath ...
0
votes
0answers
29 views

Is it bad practice to use the message digest of the plaintext as the initialization vector? [duplicate]

Data is being encrypted in a database. A message digest is being created for deduplication purposes. Is it ok to use the message digest that will be the key of the table that houses the encrypted ...
0
votes
0answers
250 views

Simple two round feistel chiffre

I am currently learning for a exam in cryptgraphy. I now try to understand the Feistel Cipher with two rounds. I do not have any information on what the functions are actually doing. The following ...
1
vote
0answers
57 views

2 round GOST_28147-89 cipher distinguisher

So, here is the scheme of how this will look graphically: The deal is to present distinguisher for this cipher. First of all here is my drafts: Way 1 Assume that distinguisher displays in ...
2
votes
2answers
129 views

Why is ECIES complex?

Wouldn't encrypting a message with AES, then encrypting the (randomly generated) AES key and IV with the EC public key suffice? What attack vectors does ECIES protect against, that an AES-then-EC-...
0
votes
1answer
160 views

1024 RSA Hash Signature attack. Forge a valid signature

I have an RSA signature of 1024 bit where i know the following: Public modulus N Public exponent (0x03) Cypher message Summary: An MD5 hash is calculated from a collection of byte and is used as ...
5
votes
1answer
172 views

Fast 128-bit MAC with second preimage resistance?

I have an application that needs a fast 128-bit MAC to guarantee message authenticity in a protocol. I would like to reuse this MAC value as a binding identifier, so that even those who know the key ...
3
votes
2answers
356 views

Definition of authenticity

I came across various definitions of what authenticity means in cryptography. I would like to know which one is correct. The first definition - the one I always used - is the following: Data ...

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