All Questions
0
votes
2answers
24 views
Proper Way to Encrypt Data with Two Keys?
I'm going to develop a system that will have two keys. One supplied and generated by the system that's specific to an individual user and one from the user.
I plan on using AES.
Does it make sense ...
3
votes
1answer
111 views
How random are comercial TRNGS
I'm thinking about buying an USB TRNG. The question is: How do I evaluate it's randomness ? I'm sure some are better than others but which is which ? Are thermal-noise better than radio-noise TRNGs?
0
votes
1answer
32 views
Recommended skills for a job in cryptology
First let me apologize if this is an ill posed question. Let me also note that I do not in any way seek a comprehensive answer, simply your thoughts on what makes for a valuable asset to a company ...
1
vote
2answers
96 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)
...
1
vote
1answer
24 views
How does the birthday attack work in AUTH and UF-CMA games?
In the AUTH and UF-CMA games, an adversary is required to forge a ciphertext or message/tag pair to win the game. Given an encryption scheme $E$ and a PRF $F$, let $\hat{E} = C || F_k(C)$ and $C = ...
1
vote
0answers
44 views
What is the fastest elliptic curve operation f(P) in affine coordinates such that f^n(P)=P only if n is large?
I'm working with the affine representations of points of a Koblitz curve.
I've read many papers that show that computing some functions, like $f(P)=3P$ can be computed faster than the standard way. ...
-2
votes
0answers
29 views
Decrypting the Encrypted hex applcation data with encryption keys [closed]
I am having all the keys,
...
-3
votes
0answers
35 views
RSA decryption from ciphertext using private key [closed]
I am sniffing a client side application traffic and I found some encrypted data. I am not able to decrypt it. Information which I have is
Public Key:
...
3
votes
2answers
156 views
Why is SRP not widely used?
SRP seems to be a very good password authentication protocol, compared to any other things used now. So why is there no popular implementations, or even no working secure implementations?
I tried to ...
7
votes
1answer
184 views
Security of pairing-based cryptography over binary fields regarding new attacks
In the last week, the discrete logarithm problem was broken for the binary fields $\mathbb{F}_{2^{(14 \times 127)}}$ and $\mathbb{F}_{2^{(27 \times 73)}}$.
Pairing-based cryptography using binary ...
2
votes
1answer
86 views
Hill-cipher, disordered alphabet
I am going to apply a simple substitution cipher to my input, then encrypt the result with a Hill cipher. How can this be broken, in a chosen-plaintext threat model?
In other words, instead of the ...
-2
votes
2answers
65 views
Perfect Secrecy, two Definitions
I'm reading the proof of the implication "Def 2.1 $\Rightarrow$ Def 2.4" in these slides about Adversarial Indistinguishability and Perfectly-Secret Encryption. I have a doubt in the slide 10. Here it ...
-2
votes
0answers
40 views
Is the likelihood of a birthday collision linear (evenly distributed) for all ciphers? When are they not?
When discussing the Birthday Principal, in combination with the pigeon hole principal, it was argued that an uneven distribution of birthdays (bias for September and any Tuesday of the year) made ...
0
votes
1answer
95 views
Do I need to keep a 64-bit version number secret?
Assume the following structure:
version | iv | ciphertext | HMAC(version | iv | ciphertext | ..., key)
The version starts out ...
1
vote
1answer
85 views
How much data can I encrypt with AES before I need to change the key in CBC mode?
In my cryptography class, the instructor suggested that in order to give the attacker a minimal advantage of $1/2^{32}$, we have to change the key after $2^{48}$ blocks are encrypted.
It seems that ...
3
votes
2answers
75 views
What are the potential security impacts of using CRAM-MD5 for Emails, when not using an SSL connection?
Background: My current server-provider tells me it's no problem to store the passwords in plain-text in the database, saying he has to do so because they use CRAM-MD5 for email authentication. But ...
6
votes
1answer
174 views
Is Wikipedia's table about SHA-2 collisions correct?
I was looking a Wikipedia article on SHA-2, and the "Comparison of SHA functions" table seems to indicate that SHA-2 is less secure than SHA-1.
Is this true, or is the table wrong / misleading?
...
0
votes
0answers
53 views
how many bit flips current computers can carry per second? When brute force is hard?
How many bit flips the fastest current computers can accomplish per time unit? i.e per second. I am trying to find when brute force attacks are considered infeasible. The reason I chose bit flips is ...
-1
votes
1answer
65 views
What key length is required to keep simple keyed “hash” secure?
In a previous question, I described a particular keyed "hash" that mapped a 5-digit input code into a 5-digit output code. It used a 8-bit key which is very insecure - more than 99% of the time, you ...
0
votes
2answers
109 views
Physical Level Encryption
What types of algorithms that are capable of signing a message are out there that run on a physical level, e.g. lacking the infrastructure of a standard PC, no memory, processor or motherboard in the ...
-2
votes
0answers
56 views
One time Pad Adversary
I like know Why $Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = 1/2$, when $\Pi$ is a One Time Pad. I trying:
$$Pr[\mathsf{PRIV_{EAV}}(\Pi,A,n)=1] = Pr[b'=0|b=0]Pr[b=0] + ...
5
votes
3answers
573 views
What is the recommended replacement for MD5?
Since MD5 is broken for purposes of security, what hash should I be using now for secure applications?
1
vote
1answer
108 views
Are there any hand ciphers not obsoleted by computer cryptanalysis?
Computerized cryptanalysis has obviously made formerly "secure" hand ciphers like Playfair, Four Square, and the Hill Cipher obsolete because they can be defeated in seconds. But is there a hand ...
2
votes
1answer
84 views
Is this algorithm secure?
I recently found this site, proposing a hashing algorithm for passwords.
They describe the following:
pad the password on both sides with SHA1(email) to ...
1
vote
3answers
92 views
Is Base64(SHA1(GUID)) still unique like the original GUID?
Basically what the title is; GUIDs are unique by design. If you run the GUID through SHA1 and then Base64 the hash, will the resulting string have the same guaranteed uniqueness as the GUID, or not?
0
votes
2answers
62 views
Why this k parameter is in unary in adversary PPT algorithm? [duplicate]
While reading some text on cryptography, I found that algorithm $A$, that the adversary (called Eve by convention) runs to break the cipher message, needs two parameters, candidate message ($y$) and ...
-4
votes
1answer
43 views
How to calculate cycles per byte [closed]
I have this data:
processor clock frequency: 2,1 ghz
message length: 16 byte
Speed: 4,3 Mbytes/s
how can calculate cycles and cycles per byte?
1
vote
1answer
88 views
Polynomial multiplication and division in 2^128
I want to multiply and divide polynomials, and implement the extended Euclidean
algorithm for polynomial greatest common divisors, over a Galois Field of size $2^{128}$. Moreover, I want to use the ...
3
votes
1answer
99 views
Alternatives to HMAC + CBC?
I'm looking at using HMAC + CBC. The combination looks like this:
ciphertext = AES256(text, k1)
data = HMAC-SHA256(iv | ciphertext, k2) | iv | ciphertext
Where:
...
2
votes
1answer
77 views
How does OAEP improve the security of RSA?
The heart of OAEP algorithm used for RSA encryption are the cryptographic hash functions $H$ and $G$.
Does everybody (so also an adversary) know these functions?
If YES: How does it help the ...
3
votes
1answer
60 views
When truncating an AES MAC value by “w” , how do I justify that “w” is still negligible?
I'm taking an online class on cryptography at corsera.org / Stanford, and the professor is explaining that it's OK to truncate an AES MAC to $w$ bits as long as $1/2^w$ is still negligible (say $w ...
16
votes
1answer
346 views
Selective format-compliant JPEG encryption?
I am working towards building a format-compliant encryption system for pictures. The aim of it is to be able to obscure specific areas of a picture (i.e. faces, car license numbers...) while keeping ...
1
vote
1answer
102 views
Is this a sensible cryptographic protocol intending to reduce the impact of compromised security?
I'm in the process of designing a cryptographic protocol which will reduce the impact an attacker will have if they gained root access to a server storing data.
The basic crux of it is that keys ...
0
votes
2answers
82 views
Generate fixed length cipher text from arbitrary length plaintext
Using an encryption algorithm like AES, is it possible to generate a fixed length cipher text no matter how long the plain text becomes?
2
votes
2answers
110 views
Generating IV in TLS 1.2
I'm writing a TLS 1.2 implementation (in C#) using a custom protocol.
My question is how to generate the IV attached to each message, I don't want to use RandonNumberGenerator because I've heard it ...
1
vote
2answers
118 views
Help me describe/identify this challenge-response protocol/algorithm?
My area of expertise is reverse engineering, specifically embedded systems. I do attack cryptographic systems, but this largely involves key recovery or exploiting the implementation.
I was asked to ...
0
votes
2answers
156 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?
3
votes
1answer
161 views
Understanding Feldman's VSS with a simple example
I'm trying to understand Feldman's VSS Scheme. The basic idea of that scheme is that one uses Shamir secret sharing to share a secret and commitments of the coefficients of the polynomial to allow the ...
1
vote
2answers
66 views
Is Functional Encryption about Access Control over encrypted data alone?
Informally, In functional encryption system , a decryption key allows a user to
learn a function of the encrypted data. But all i see is that the function acts as an access control over the data.
...
1
vote
2answers
101 views
True random numbers generated by sensors
Is using sensor raw data a good way of generating true random numbers? I mean using an IPhone's gyro/accelerometer raw output as a base for generating an array of true random numbers.
2
votes
1answer
1k views
How to solve MixColumns
I can't really understand MixColumns in Advanced Encryption Standard, can anyone help me how to do this?
I found some topic in the internet about MixColumns, but I still have a lot of question to ...
-4
votes
0answers
29 views
pseudo random sequence and permutation functions [closed]
Iam doing my Master thesis in enhancing of an encryption algorithm by using of a pseudo random sequence generators to create a 16*16 shared table and apply a permutation function on it. one of the ...
0
votes
0answers
33 views
calculating beta for elgamal elliptic curves [duplicate]
Suppose we use elgamal elliptic curves for secure communication. Bob selects a prime $p$, an elliptic curve $E$, a point $\alpha$ on $E \pmod p$, and a secret integer $f$. Suppose that Bob has ...
0
votes
0answers
36 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? [duplicate]
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 the 160 bit result contains at least 128 1's?
0
votes
1answer
143 views
Anonymity in end to end encryption
Considering a scenario of anonymous data transfer between seller and buyer using proxies. If we consider that there are three proxies that are being selected by buyer to obtain data from different ...
0
votes
3answers
346 views
Is AES really used for Top Secret stuff?
I've read almost everywhere that AES-256 can be used for Top Secret material (in the US). Is it really used or is it some kind of decoy to hide the more advanced algorithm they might use ?
2
votes
1answer
243 views
Partial collisions for md5
Let $h$ be a bitstring and let $P(h, n)$ be the n-bit prefix of $h$. A partial collision of length $n$, for a hash function $H$ is a pair $(x,y)$, such that $P(H(x),n)=P(H(y),n)$.
What is known about ...
-1
votes
0answers
38 views
How to decipher this morse-like code message? [closed]
I found this little string that looks like Morse Code, but instead of dots (dits) has hearts symbols, I tried to change the hearts for dots, but I was not able to get any redable text.
...
0
votes
1answer
26 views
PKCS#11: Which CKK_types are supported by CKM_PKCS5_PBKD2?
On Solaris there's a function pkcs11_PasswdToKey() which is a wrapper of C_GenerateKey(). I made a simple test and it turned out ...
3
votes
2answers
188 views
Is there a way to do fair exchange between two parties who don't trust each other?
Let's suppose we have an Alice who knows a secret key A, and Bob who knows key B. Using their own keys, they each encrypt a message (Alice encrypts $m_A$, Bob encrypts $m_B$) with their own key, and ...
