All Questions
-1
votes
0answers
35 views
Adaptative chosen ciphertext security McEliece
I am read the paper and I found the follow Lemma2 (pp. 13)
Suposse that there exists, for any $Hash_z$ and any $Gen$, an algorithm $A$ ...
My question is Why "for any $Hash_z$ and any $Gen$"? Are ...
3
votes
1answer
136 views
Secure encrypt-then-sign with RSA
I understand that when you want to encrypt and sign data with RSA the generally recommended approach is sign-then-encrypt.
However, I have encrypted data that I need to sign, to prove the author of ...
1
vote
0answers
61 views
Is OAEP reversible?
Given nothing more than some integer $m =$ OAEP($M$), is it possible to recover the original plaintext $M$? In other words, without being given the hash functions or the random string used for ...
-1
votes
0answers
57 views
Tools to assist learning cryptography in real world [closed]
Hey I am new to cryptography and I wanna see how cryptography works in the real world. Suggest me some tools which will help get me a better idea about cryptography. (If it were networking I would ...
3
votes
1answer
81 views
implementing long term archive encryption
Let's say I want to create private archives for the long term (e.g. more than 30 ). The archives' sizes could be anywhere from 1 GB to 30 GB. As far as I understand I could go down two ways:
The ...
1
vote
1answer
74 views
How can a key pair be derived from an arbitrary hash?
If I correctly understand the concept of a "brain wallet" in BitCoin, you start with a passphrase, generate the hash of the passphrase, then somehow derive a public / private key from that to use as ...
-4
votes
0answers
62 views
RSA Encryption Sckeme [closed]
Can anyone help me with this question?
A and B want to exchange encrypted messages; specifically, B wants to send a message M
written in binary format to A, which needs to be encrypted. They agree on ...
1
vote
0answers
57 views
Algorithm digipass-like
I'm pretty sure there are famous algorithms for my problem, but I don't have enough knowledge in this field, so I need your lights.
Here si the problem :
Alice sends key X to Bob.
Bob has an ...
-4
votes
1answer
96 views
Indistinguishability CPA and CCA2
I am study security notions in two lecture and I am cofusing with the concepts IND-CCA and IND-CPA2. About IND-CCA in wikipedia say
Indistinguishability under chosen ciphertext attack/adaptive chosen
...
3
votes
2answers
171 views
AES - plaintext is smaller 128 bit - how to expaned?
we are currently developing a little AES implementation in a crypto-course at university.
As far as I know, AES uses 128 bit blocklength, so all data that will be encrypted will get split up into ...
1
vote
1answer
98 views
Password verification
I'm looking for feedback on whether or not this is the proper way to approach password verification without transmitting the actual password. Are there any problems with this scheme.
We are working ...
4
votes
1answer
183 views
repeating-key xor and hamming distance
I read that to break repeating-key xor you can do the following: try a keysize $n$ and compute the hamming distance between the first $n$ bits of the encrypted string and the bits $n+1$ to $2n$ of the ...
0
votes
1answer
96 views
Is this scheme a provably fair random number generation?
I have thought up a method for generating random numbers between a client and a server which I hope is fair:
The client and server decide on a range in advance, $0$ trough $n-1$.
The server ...
1
vote
1answer
48 views
What does “securely realize” mean?
I was wondering what "securely realizes" means. I see this in some cryptographic papers but I don't know what it means for a protocol to "securely realize" a function $F$. Is it just a fancy way of ...
3
votes
1answer
109 views
Combining AEAD with RSA
'Hybrid' encryption, where we combine symmetric encryption with public-key cryptography, is pretty 'tried and tested'.
To summarise, we generate a symmetric key and encrypt it using RSA. We would ...
1
vote
1answer
74 views
Which public key was used. PGP
Is it possible to find out which public key was used to generate the message?
Scenario is like this :
I got data which is encrypted with a public key. Now a "bad guy" hast the encrypted data, and ...
2
votes
4answers
188 views
Tamper-proofing log files
Problem Overview
I want to securely store log files so the contents are secret, and they can't be modified without detection.
The files will be encrypted using authenticated encryption (AES in GCM ...
-1
votes
0answers
25 views
Create groups of keys [closed]
I looking for a solution to encrypt, sign documents or email a key group and send to one customers. The group of keys are had already created user keys and I would like to use them.
Is not an option ...
1
vote
1answer
55 views
What happen if a asymmetric crypto-system deals with only one key
Assume there is a crypto algorithm that deals with matrices to encrypt and decrypt. Regardless of the specification of such algorithm, what if the algorithm assumes that two parties can securely agree ...
-2
votes
0answers
58 views
Patterns in primes, listing? [closed]
Is there a listing of all the patterns people have found in prime numbers? I think I have found a new one and want to check against what is out there to make sure.
Yes I know this sounds very very ...
4
votes
2answers
178 views
Are cryptographic hash functions perfect hash functions?
For a cryptographic hash function and input values of shorter length than the hash function output, it's pretty obvious that there should be as few collisions as possible. But are there guaranteed to ...
2
votes
1answer
92 views
Attacking historical ciphers methodology
It's more a theoretical question of how would you approach it. All you know about the ciphertext it's was generated with a historical cipher. The ciphertext appears to be random, BUT it's divided into ...
1
vote
4answers
140 views
Using the output of a stream cipher, how to guarantee the integrity of 4 bytes of data?
I am designing a simple and secure stream communication protocol. My idea was to build each message sent to the wire as:
(message size || clear text || UHASH(message size || clear text)) $\oplus$ ...
2
votes
1answer
150 views
SHA256 HMAC brute force with chosen plaintext attacks
This is a follow up to Is It Possible To Reconstruct a Cryptographic Hash's Key
I am using a SHA-256 HMAC function on a single-word input: sha256hmac(privatekey,word) = output. The private key length ...
4
votes
1answer
153 views
Quality of randomness on a Linux system with haveged
Has anyone checked if using haveged, a Linux daemon which uses the HAVEGE algorithm, changes the non-deterministic properties of the random data from ...
3
votes
2answers
139 views
Using the same secret key for encryption and authentication in a Encrypt-then-MAC scheme
Is it a weakness to use a single shared secret for protecting messages using a Encrypt-then-MAC scheme?
Assuming a system is using AES-256-CBC and a SHA1-HMAC and the same secret key for both ...
2
votes
3answers
157 views
Is it possible to work out the hash algorithm from a list of known message-hash pairs?
For example, in my situation I know hash(20) = 486e9638177faf1f34e49910491b77af.
I also know the hashes for all values from 0 to 20.
Is it possible to work out the ...
2
votes
0answers
90 views
LT codes with Homomorphic hashing
I have been working on a project implementing LT codes with Homomorphic hashing (inspired from http://blog.notdot.net/2012/08/Damn-Cool-Algorithms-Homomorphic-Hashing and ...
0
votes
0answers
16 views
LT codes with Homomorphic hashing [duplicate]
I have been working on a project implementing LT codes with Homomorphic hashing (inspired from http://blog.notdot.net/2012/08/Damn-Cool-Algorithms-Homomorphic-Hashing and ...
2
votes
3answers
165 views
The utility of elliptic curve cryptography
Suppose that the only public key cryptography schemes that we knew were Diffie Hellman, RSA and ElGamal. How much would this set civilization back? Are there important applications of elliptic curve ...
1
vote
1answer
67 views
Connections between Instance Hiding and Fully Homomorphic Encryption
Another approach taken by researchers for carrying out computations over encrypted data is Instance Hiding.
In brief, If a user wants to outsource the computation of a function for a particular input ...
1
vote
1answer
69 views
Requiring a “supervisor” key pair and a “user” key pair to decrypt multiple-recipient messages
I've been toying with some encryption scenarios recently. One of the hard ones I came across is a multi-party system.
So we have
Bob -- The person who sends the message (and knows it's recipients)
...
4
votes
0answers
138 views
Prove that textbook RSA is susceptible to a chosen ciphertext attack
Given a ciphertext $y$, describe how to choose a ciphertext $\hat{y} \neq y$, such that knowledge of the plaintext $\hat{x}=d_K(\hat{y})$ allows $x=d_k(y)$ to be computed.
So I use the fact that the ...
2
votes
1answer
70 views
Addition with Shamir secret sharing
When performing Shamir secret sharing I'm trying to find $z_i$, such that $z = x + y$. Where $n = 6$ and $t = 3$.
I believe this would be the correct solution (correct me if I'm wrong):
Each party ...
3
votes
1answer
125 views
Triple-DES Brute Force
Shannon's paper states:
A system is pure if all keys are equally likely and if for any three
transformations, $T_i$, $T_j$, $T_k$ in the set, the product
$T_iT_j^{-1}T_k$ is also a ...
5
votes
1answer
186 views
A lower bound on the insecurity of CipherCloud?
CipherCloud claims to support , among other things, searchable encryption. A bunch of speculation seems to suggest they did this via some breathtakingly incompetent means( unfortunately such ...
2
votes
2answers
127 views
Chain several RSA encryptions without increasing the message size
I would like to be able to encrypt the output of RSA with RSA again without having the output grow in size over time.
In other words, I have some data $D_0$ which I want to encrypt with RSA: $D_1 = ...
15
votes
1answer
400 views
Should I trust CipherCloud? [closed]
Should I trust CipherCloud's system for "homomorphic encryption" of data in the cloud?
Has the security of their system been subject to peer review or other cryptanalysis? Is there any known analysis ...
5
votes
2answers
183 views
Is encrypting a single 128 bit block with AES ECB “safe”
I want to encrypt a small piece of data that is less that 16 bytes in size (think SSN), and I'll be using a 256bit encryption key. The typical suggestion is to never use ECB, but if there is just a ...
1
vote
1answer
65 views
How to learn the first bit of m in padded RSA
Consider the following version of padded RSA encryption, where encryption of $m$ is done by setting $m′ = (0^k~||~r~||~00000000~||~m)$ for a random $r$ (of length 8 btyes = 64 bits) and then computing ...
1
vote
1answer
107 views
AES AddRoundKey
Looking at the first step of AES encryption I see that we XOR the key with the plaintext block. Why is the actual key involved at all, why not just use the round keys derived from the key schedule?
3
votes
2answers
191 views
What is the best way to store sensitive information on the client?
I am very inexperienced with cryptography and would like some advice on how to store some sensitive information on client machines.
I have some information stored in a central database on my server. ...
2
votes
1answer
98 views
Can prepending “junk” be equivalent to an IV when encrypting using CBC?
We are encrypting a small positive integer (1-1000) with a constant key using AES256 encryption. We are considering two approaches to make this secure; use an initial vector (which we then need to ...
1
vote
0answers
51 views
PKC McEliece + $S$ + $P$
I am trying implement the McEliece crytosystem in SAGE. My question is How I will be able to choose the appropriate matrix $S$ and $P$?. I ask this because when I trying obtain the vector $\hat{m}=mS$ ...
0
votes
0answers
124 views
How can I become familiar with the logic syntax used in Cryptography papers? [closed]
I'm having to write a 5000 word essay on Cryptography, and many (if not all) of the papers I've read on the topics have logic syntax I simply don't understand.
How can I become familiar with the ...
3
votes
2answers
68 views
GPG and PAR2 error correction data from the plain archive, will it compromise security?
I have the following scenario:
Archives compressed with 7z, hundreds of MiB in size
GPG to encrypt the archives (binary, without ASCII armor)
PAR2 to create error correction data
Question
1. ...
3
votes
0answers
80 views
How can scrypt be improved to counter GPU mining
I know scrypt was designed to lessen the GPU/ASIC advantage.
We now have litecoin as a real-world example of this. However, it hasn't worked out perfectly. Most coins are mined by GPUs, although the ...
1
vote
2answers
66 views
How secure is passing a MAC to Python's random.seed before using random.choice to generate a MAC?
I'd like to use Python's random.choice seeded with a HMAC-SHA1 tag to generate a MAC encoded in a variable set of chars.
...
1
vote
1answer
47 views
Why are the Davies-Meyer and Miyaguchi-Preneel constructions secure?
The Davies-Meyer compression function $h(H, m) = E_m(H) \oplus H$ is said to be secure. So too is the Miyaguchi-Preneel compression function $h(H, m) = E_m(H) \oplus m \oplus H$. Why are these ...
2
votes
2answers
130 views
Why is $h(H, m) = E(m, H) \oplus m$ insecure?
I am taking a cryptography class on Coursera. I learned that the compression function $h(H, m) = E_m(H) \oplus m$ is insecure (even though other variants like DaviesÂ-Meyer or Miyaguchi-Preneel are ...
