All Questions
0
votes
3answers
524 views
LFSR for small numbers with large periods
I want to generate a few random numbers using an LFSR. However, the LFSR output depends on the number of taps, so for a large period I use large (relative) number of bits. This causes the numbers to ...
0
votes
1answer
77 views
True 128bit secured password length?
assume we say 128bit keys are secure so a 16 character long password is safe, but if i even use lower case and upper case letters with numbers and special characters on my keyboard its about 80 ...
0
votes
1answer
66 views
Tweaking textbook RSA to make the encryption a Pseudorandom function
Lets say I want to tweak/alter the textbook RSA encryption function to create a pseudorandom function by pre-processing the input.
Suppose I do something simple like add 2 to the input before ...
0
votes
2answers
100 views
Is this how padding can work?
So for block ciphers you need a fixed size block.
If the plaintext length is not a multiple of the block length then you need to pad it.
One way you could do this is that for the last block you just ...
0
votes
2answers
289 views
decrypt AES without whole key
Is there a way to decrypt a AES cipher Text which was encrypted twice with some key, when having a part of this key? (the last 3 bytes of the key are missing)
0
votes
3answers
73 views
MISTY1 Implementation error
I am trying to implement MISTY1. It's RFC, RFC2994, contains psuedocode that I basically copy and pasted into Code::Blocks. However, I managed to mess that up somehow. After 2 days, I still have not ...
0
votes
2answers
124 views
Cryptographical formalization of computational privacy
Yesteryears problems of communication privacy has been well defined in cryptography through Asymmetric cryptography.
Due to rise in Cloud computational model , computational heavy tasks are being ...
0
votes
2answers
154 views
Idea for user/pass hashing to prevent rainbow tables, would it work?
I'm very new to cryptography (and security in general, for that matter), but I had an idea that I'm sure is very flawed, but is worth asking. If a computer user, online account, etc, needs to verify a ...
0
votes
2answers
132 views
CPA distinguisher for matrix multiplication in GF(256) with randomized padding
What is the best CPA distinguisher for the function $F_k:\{0,1\}^{8n}\to\{0,1\}^{16n}$ described below?
Let $E_k$ be a $2n\times2n$ matrix with elements in $GF(2^8)$, selected by generating bit ...
0
votes
2answers
85 views
risk of attacker decrypting RSA ciphertext without public or private key
As I describe in my previous question I am trying to decide if it's worth it for me to use the Offline Private Key Protocol in creating some long term private archives, instead of just going with a ...
0
votes
2answers
89 views
Do I need to know the “mode of operation” to decrypt a message encrypted with a block cipher?
If I have received an AES encrypted message, and if I do know the key with which it was encrypted, do I also need to know the mode of operation with which it was encrypted in order to decrypt it? My ...
0
votes
1answer
71 views
Encrypting and Decrypting a 19-digits long BigInteger
How can I take a maximum 19-digits long BigInteger and encrypt it with the following rules:
The result must be based on digits and lower-case English letters ...
0
votes
1answer
126 views
Possibility of factorisation of rsa modulus due to vulnerability in java implementation code
Below is my implementation of the RSA algorithm. Actually I'm choosing the private key (d) instead of public key (e) and computing the public key.It is working fine but
I want to know if this is a ...
0
votes
2answers
77 views
Is solving a modular linear equation a hard problem when the coefficient is not an invertible element?
Assume that we have a linear equation like this:
$$ax=b \pmod n$$
when $x$ is the unknown, and $a$ is not an invertible element in $n$.
is finding $x$ a hard problem?
(by solving I mean finding an ...
0
votes
2answers
128 views
Why nobody considers counter re-keying as a standard Block Cipher Mode?
One of the simplest possible cipher modes is setting each successive key as a function F of the previous one.
K[0] = Master key
C[i] = E(K[i],P[i]), K[i]=F(K[i-1])
This is similar to the counter ...
0
votes
1answer
94 views
Why are RSA keys encoded with ASN.1 for TLS?
Browser vendors use ASN.1 encoding for RSA certificates in the TLS protocol. RSA public keys are just a number, so why do we need encode them to something else? That increases the risk of security ...
0
votes
1answer
129 views
Bitcoin, couldn't a miner steal money? [closed]
What prevents a miner's block from being accepted across the network if the hash checks out when miner forges transactions in the block?
For example, lets say I'm mining and I want to steal money ...
0
votes
1answer
69 views
AES 128bit round level recommendation
we don't want change standard just after every attack, now for AES 128bit blocks i think 16 round is secure, but what is best round amount ? we had attack for 7 round then 10 round and it going so on ...
0
votes
1answer
111 views
Diffie-Hellman is Post-quantum secured?
If Alice and bob have a secure channel for key-exchange and mallory don't man-in-the-middle attack them but in the future eavesdrop connection and see the key exchanged, can mallory break it like RSA ...
0
votes
1answer
75 views
Does a break in a collision resistance property of a hash function by definition implies an attack at the first pre-image attack?
Is there a formal security proof in the shape of reduction that states that if an attacker manages to break the collision resistance property of a cryptographic hash function (a random oracle) he will ...
0
votes
2answers
118 views
Breaking RSA, given a special kind of oracle that decrypts related ciphertexts for us
Let $c=E^{RSA}_{e}(w)$ be the ciphertext belonging to the plaintext $w$ if an $RSA$ system is used. Assume that the public exponent $e$ satisfies $e \le 10$. Furthermore, assume there is an oracle ...
0
votes
2answers
55 views
Quantum key distribution and OTP
Why is QKD usually associated with OTP ?
QKD is about key distribution, where as OTP is about using key as long as message to get perfect secrecy, can any one explain how they are related ?
0
votes
1answer
97 views
How do I calculate the maximum plain text length allowable for a certain cipher text length?
I am encrypting and storing sensitive values in the database. I have a set max length in the database, but in order to provide useful user feedback, I'd like to know the max input I should allow for a ...
0
votes
2answers
129 views
Is stretching hash several times basically the same as bcrypt?
As I understand it, the main advantage of bcrypt is stretching so it becomes slower to crack overtime. But, is using a "good enough" algorithm (e.g., SHA-2 family) then stretching until it's slow ...
0
votes
3answers
209 views
Should I use md5 for my new application?
MD5 is a very fast hash and its output is short and easy to store. Should I use it for my non-security-sensitive application?
I don't think so, but I can't seem to convince anyone else that this is ...
0
votes
1answer
362 views
AES GCM symmetric encryption of data at rest in c#, ciphertext much longer than plaintext
I've written encryption/decryption routines using AES GCM. Code can be found here.
I recently realized that the cipher text is longer than I believe it should be. It should add the tag and IV onto ...
0
votes
3answers
109 views
Is it possible to ensure security with zero pre-shared information?
Is it possible to secure a communications channel against both passive (sniffing) and active (injecting / MitM) attackers without either legitimate party knowing any pre-shared information?
I know ...
0
votes
1answer
731 views
Counter Mode in Advanced Encryption Standard(AES) Algorithm
In Advanced Encryption Standard, If I used "Counter Mode", in it's nonce value, what should I do?
ex. should I divide the nonce value into two? ex. I have 128-bit of nonce, should I divide it from ...
0
votes
1answer
122 views
Can we trust digital signatures?
Consider that Alice wants to send a digitally signed message to Bob.
Mallory might be able to publish his public key under Alice's name and then impersonate Alice to send a message with an apparently ...
0
votes
1answer
104 views
RSA/DSA: Wouldn't it make sense to sign using decoding the data hash?
Why is encoding using the private key used for signing? Wouldn't it make sense to keep the premise, that private is for decoding and public is for encoding? i.e. create a hash and threat it as a ...
0
votes
2answers
299 views
What is the time complexity of the RC4 encryption & decryption algorithms?
I'm trying to figure out what the time complexity of RC4 encryption & decryption algorithms is, in big-O-notation.
0
votes
1answer
155 views
Cryptographically strong pseudo-random seq. generators
If a pseudo-random sequence generator is built so that it uses an n-bit seed and outputs a string that is of length x. Let's say one wants to generate a bit string of length y and uses the previous ...
0
votes
1answer
114 views
BigInteger in Java and Randomness
I'm looking for some PRNGs and as I have been using Java for a long period of time I thought that the BitInteger class together with the Random class could both generate some large pseudo random ...
0
votes
2answers
322 views
Can md5 be used for encrypting data?
I know that md5 shouldn't be used for password hashing because of collisions and possibility of making dictionary attacks e.g. using rainbow tables. But what about ...
0
votes
1answer
765 views
Store user passwords in database using Java Application
I want to store user's password details in Database. My project is in Java. I want to know the best way of storing passwords and other inportant information like user
0
votes
1answer
55 views
What is a fair exchange scheme?
The Wikipedia entry Fair exchange has only two lines, and the only paper I can find describing such a protocol is extremely complicated.
Is this a new field in cryptology or can someone give an ...
0
votes
1answer
39 views
Is the DES algorithm in OPENSSL random?
Look at the hex dumps of encrypted1.bin and encrypted2.bin . They both have same password A which was used to encrypt sampletext
...
0
votes
1answer
58 views
How to hash a structure that needs to include that hash's outcome?
so I am busy writing a TCP protocol in which I send a "packet header" with each packet of data. This packet header is a structure that contains information about the data that was sent. I want to ...
0
votes
1answer
45 views
chaining rsa with ecies
In an answer to a previous question it was suggested that one way to protect your asymmetrically encrypted AES-256 keys, from say a solution to prime factorization, would be to chain asymmetric ...
0
votes
1answer
86 views
decryption many time pad
I have eleven ciphertexts that were encrypted with the same key (which I don't know). I want to decrypt the last ciphertext. I read similar question like Many time pad attack but I can't solve my ...
0
votes
2answers
75 views
Using salted hash as password for easy memorization without reuse?
I had an idea earlier:
Secure passwords are a) long, and b) unpredictable. A hash is both of these. Would it be safe to reuse a key between sites, and include the site's name as a salt? For example:
...
0
votes
2answers
66 views
Voice Call Safety [closed]
When i was dealing with an assistant of my bank through mobile call, she asked me to insert my bank login code after a beep.
I was wondering if this procedure is secure against a Man In the Middle ...
0
votes
1answer
78 views
In which disciplinary kind can Cryptography be put?
Is it a multidisciplinary? an interdisciplinary? a cross-disciplinary? or a trans-disciplinary?
what are the basis put to describe each kind?
I mean how can we infer by which disciplinary field we can ...
0
votes
2answers
211 views
Even passwords are vulnerable to hash collision attacks?
As stated in this page large documents hashed using md5 maybe vulnerable to collision attacks. My question is even passwords of 6-30 character are vulnerable to such hash collision attacks? If yes, is ...
0
votes
1answer
51 views
Efficient algorithm for remainder calculation over prime field for ECC implementation?
I am working on 224-bit elliptic curve cryptography. In this 224-bit * 224-bit multiplication results 448-bit output. I am reducing 448-bit into prime field range( prime number $2^{224}-2^{96}+1$) ...
0
votes
1answer
80 views
Can one detect if two pairs of elements in Zp have the same exponential relation?
Suppose that $p$ is a safe prime of 2048 bits ($p = 2q + 1$, and $q$ is prime).
Suppose that one is given two pairs $(x_1, y_1)$ and $(x_2, y_2)$ such that:
$y_1 = x_1^{r_1} \pmod p$
$y_2 = ...
0
votes
1answer
104 views
How to solve the reverse of an equation that uses MOD?
I've been tasked with reverse engineering an unknown crypto function. The function uses the following constants:
$a=380951$:
I noticed that this is a prime number
$b=3182$:
I noted that this is a ...
0
votes
2answers
124 views
AES encryption with shared IV
Sorry about the horrible title, didn't now what to say.
I'm trying to avoid having to send an IV with every message purely to keep packet sizes down, so I thought of a method to establish a "IV ...
0
votes
1answer
79 views
brute force attack on KDF vs KEY
if we believe 256bit keys are secure in AES against any brute force attack, is that possible we use a KDF (convert user's weak entered password in truecrypt into a fixed AES key) with too much round ...
0
votes
1answer
79 views
Secure way to compare two secret numbers without disclosing them?
For example, two people want to know who is the older, without disclosing their age. Is there a secure way to do this without a third party involved?
