All Questions
2
votes
2answers
243 views
Can I build a secure tweakable block cipher from a normal one by adding key and tweak?
Let (E,D) be a secure block cipher.
Consider the following tweakable block cipher:
...
2
votes
1answer
306 views
Is there a standard for OpenSSL-interoperable AES encryption?
Many AES-encrypted things (files, strings, database entries, etc.) start with "Salted__" ("U2FsdGVkX1" in base64).
I hear it's some sort of OpenSSL interoperability thing a b c.
Is there some ...
2
votes
0answers
73 views
How to properly format a PGP Message Block?
As sort of a follow up to my (currently) unanswered question, if it is correct, how do i properly calculate and format the packet that actually stores the data being encrypted? I thought I knew what I ...
2
votes
3answers
225 views
PRNG taking advantage of very large seed
Can anyone suggest a good (CS)PRNG algorithm that takes advantage of having a very large (ideally arbitrarily large) seed? I'd like to use several kilobytes, perhaps several hundred kilobytes, of ...
2
votes
2answers
297 views
Capacity of Advanced Encryption Standard in terms of File Encryption
what is the capacity of AES in terms of File Encryption?
is it really good to encrypt a large files in AES? ex. I am encrypting a 8GB of File... is it still good to used AES?
is it still good to used ...
2
votes
3answers
270 views
Can I pre-define the points in Shamir's Secret Sharing algorithm
With Shamir's secret sharing is it possible to pre-define the points returned by the algorithm?
For simplicity if I have (k, n) where k=2, and n=4, and I have the points X,Y,Z, and Q. Can I create ...
2
votes
1answer
93 views
Why are there $ signs in my passwd file?
I am trying to get access to my eReader and I managed to get the passwd file.
...
2
votes
2answers
291 views
How to get the keyword from a keyword cipher?
I was given a ciphertext and now I am trying to break it via looking for the keyword.
This is a keyword cipher. So:
PlainEnglish: ABCDEFGHIJKLMNOPQRSTUVWXYZ
If ...
2
votes
1answer
267 views
What is the harm if I publish an encrypted RSA private key publicly?
What is the harm if I publish an encrypted RSA private key publicly? Or in this case, what is the harm if I publish many thousands or millions of them?
Assuming that the private key is encrypted ...
2
votes
1answer
2k views
How to use RCON In Key Expansion of 128 Bit Advanced Encryption Standard
I have a question about RCON
here is my illustration...
this is the 128 bit key..
...
1
vote
1answer
49 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 ...
1
vote
1answer
198 views
What does the expression $1^n$ mean as a function argument?
In a paper about predicate encryption or attribute based encryption, the setup function is mentioned with the $setup(1^n)$ or $setup(1^l)$. I want to know what is meant here.
Is it multiples of ones ...
1
vote
1answer
88 views
How large should a Diffie-Hellman p be if the messages are encrypted?
How large should the prime $p$ and generator $g$ values be in a Diffie-Hellman handshake if the messages are encrypted.
If the key that encrypted the Diffie-Hellman messages becomes compromised, ...
1
vote
4answers
99 views
How to perform Multiplicative Inverse Modulo in IDEA
How to perform the Multiplicative Inverse Modulo in International Data Encryption Algorithm?
I cannot understand on how to perform it...
ex. I have a value of "cf80" and the value that is appearing ...
1
vote
1answer
69 views
Security relevance of random factor in Paillier
In the Paillier cryptosystem [1] the encryption of $m \in \mathbb{Z}_N$ with randomness $r \in \mathbb{Z}_n^*$ is $c = g^m r^n \bmod{n^2}$.
The additive-homomorphic property of the system shows that
...
1
vote
1answer
73 views
Non-cryptographic hash function as MAC for stream ciphers
I understand that for a stream cipher to be useful, there must be a way to verify that the message was not tampered with (bits were flipped by an attacker).
So, instead of using some cryptographic ...
1
vote
2answers
131 views
AES Key Length vs Block Length
This answer points out that certain key and block lengths were a requirement for the AES submissions:
The candidate algorithm shall be capable of supporting key-block combinations with sizes of ...
1
vote
1answer
131 views
using Post-quantum asymmetric ciphers instead of RSA
We can't trust RSA to encrypt our Emails so what is best post-quantum cryptography system as alternative for RSA which provide good security and don't be breakable? because McEliece cryptosystem looks ...
1
vote
1answer
174 views
How do unkeyed hash functions (for MDCs) provide security?
Unkeyed hash functions are, by definition, hash functions computed without a key. SHA-1 is an example. MDCs (message digest codes) are a subclass of unkeyed hash functions. How are unkeyed hash ...
1
vote
1answer
287 views
How can I implement the “Multiplication Modulo” and “Addition Modulo” operations in IDEA?
I am currently working on IDEA (International Data Encryption Algorithm), and I don't know how to perform Multiplication Modulo and Addition Modulo.
This is how IDEA operates:
IDEA operates on ...
1
vote
1answer
188 views
What happens to the entropy of a password when you hash it?
For example, if the entropy of a password is 30 bits, what is the entropy of the password when you hash it with MD5?
1
vote
2answers
117 views
RSA keys finding when messages are known
I have this situation, where, in a game, people send messages to each other (game moves etc...) These messages need to be encrypted, and should only be readable by the destination person. I am using ...
1
vote
2answers
211 views
Avalanche noise RNG for one-time pad use
I came across this little HRNG widget and was really intrigued as I have been looking for a decent but afordable source for truly random bits to use in a one-time pad.
The question is, would a HRNG ...
1
vote
1answer
188 views
implications of SSH server key compromission when authenticating users against a public key
Friday we had a disagreement with a colleague of mine about the implications of SSH server key compromission
The question was stated as this :
What could a hacker do while provided with the SSH ...
1
vote
1answer
255 views
How to implement order preserving encryption or order preserving hashing
Does anybody know any free implementation of either order preserving encryption or order preserving hashing? I've found some codes like CMPH but I need to dynamically add new DATA and that's why most ...
1
vote
4answers
395 views
Is my pseudo-random initialization vector secure?
How can I know if I am generating a secure pseudorandom initialization vector?
Currently I am planning to generate a pseudo-random initialization Vector using current date and time - is this secure ...
1
vote
3answers
433 views
Which attacks can be avoided by the use of OFB instead of ECB?
For a file encryption program, I was told to use Output Feedback mode (OFB) instead of ECB (Electronic code book) mode.
Which attacks can I avoid by this choice?
1
vote
2answers
239 views
Complexity of ECB and OFB
What is the complexity of ECB in terms of Time and Memory?
and also in OFB? I can't find it in the internet, so I decided to ask it in here.
1
vote
1answer
51 views
Proving item association without revealing one of the associated items
I'm a total noob when it comes to cryptography but I believe this falls under the "zero knowledge" category.
I have two associated pieces of information:
tag — known by both parties. Unique per ...
1
vote
3answers
293 views
reverse of md5sum
This might be out of ignorance, I apologize, but how complex of a problem might it be to generate a file of size N whose md5sum is X?
For example,
...
1
vote
1answer
199 views
Offline anonymous electronic money systems and their cryptographical base
What anonymous offline electronic money systems exist and what are they based on? I know only one currently - eCash, based on RSA blind signatures.
1
vote
2answers
106 views
Combating traffic analysis over request-response protocols
Suppose I am to design a request-response protocol (similar HTTP). For the sake of simplicity let us assume that this is a "chat" protocol where the client can only perform two actions:
Contribute a ...
1
vote
0answers
76 views
Two untrusted party want to exchange data: how to ensure each one gets the data it needs? [duplicate]
Possible Duplicate:
Two untrusted party want to exchange data: how to insure each one gets the data it needs?
I am trying to come up with what could maybe be a novel algorithm for an ...
0
votes
2answers
148 views
SHA-1:Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output?
Is there any mathematical result that gives us the minimum number of 1's in a 160-bit SHA-1 hash output? What is the probability that a 160-bit SHA-1 hash output contains at least 128 1's?
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
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
1answer
156 views
What is the probability of breaking the AES algorithm?
I am doing a project which requires the encryption to be done using AES. Is it really possible (technically) to crack AES?
If yes, please tell me:
What is the probability of breaking AES?
How ...
0
votes
2answers
212 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
90 views
Scrypt as a KDF with one-time high-entropy input
I'm looking at using Scrypt as a KDF. Assume the following:
the input will always be high-entropy random bytes generated by a CSPRNG
the length of the input can vary from between 8 to 32 bytes
the ...
0
votes
1answer
227 views
0
votes
1answer
184 views
Blowfish: hex digits of pi used for s-boxes?
Preface: here is the official site for the Blowfish algorithm:
http://www.schneier.com/blowfish.html
The Blowfish algorithm uses an s-box, which consists of hex digits of pi (found here: ...
0
votes
0answers
63 views
Stream Cipher : Never use stream cipher key more than once [duplicate]
Possible Duplicate:
Taking advantage of one-time pad key reuse?
How does one attack a two-time pad (i.e. one time pad with key reuse)?
Denote C is cipher text, m is message, and PRG(k) is ...
0
votes
1answer
152 views
which of these is more secure (bcrypt vs srp)
OK, here's the two different ways I was thinking about making the authentication for the login thing to store the passwords securely.
The first is the following.
Client hashes password ...
0
votes
2answers
200 views
Is the Blum Blum Shub PRNG suitable to create initialization vectors?
Is it a good idea to use a Blum Blum Shub Generator to create my initialization Vector (IV) in AES-OFB (Output Feedback Mode)?
0
votes
1answer
218 views
What is the correct value for “certainty” in RSA key pair generation?
I'm creating an RSA key pair in Bouncy Castle and need to specify an int value for certainty. This Stack Overflow answer says it is a relative test for how prime the values are.
There is another ...
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 ...
-1
votes
1answer
82 views
What length should the padding be when encrypting or signing with RSA?
Does it matter what length the padding is? If so - what length should it be?
(Another point: Should it be random?)
-3
votes
0answers
82 views
Why is the basic (fixed-length) CBC MAC construction not a secure MAC when it is used on variable-sized messages? [closed]
Why is the basic (fi xed-length) CBC MAC construction not a secure MAC when it is used on variable-sized messages?
-3
votes
1answer
424 views
Advantages of each encryption mode [closed]
What is the advantages of each encryption mode to other encryption mode..
for example what are advantages of CBC to PCBC, CBC to CFB
just like that.
so that I can filter what would be the best ...
-5
votes
1answer
97 views
My Hand Cipher, Can some one tell if it secure [closed]
In easy steps how it works,
Convert txt to numbers . mod 1-26.
Generate random numbers (By my other cipher) equal to plain txt.
Write random numbers under txt numbers.
txt= LOI - txt number= 12 15 ...
