All Questions
0
votes
0answers
39 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 ...
0
votes
0answers
64 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 ...
5
votes
1answer
110 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
44 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 ...
0
votes
1answer
53 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
0answers
62 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?
-1
votes
1answer
51 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 ...
-1
votes
0answers
55 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] + ...
2
votes
1answer
68 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 ...
0
votes
2answers
100 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 ...
1
vote
1answer
102 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 ...
-4
votes
1answer
38 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?
0
votes
2answers
60 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 ...
3
votes
1answer
93 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:
...
1
vote
3answers
88 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?
3
votes
2answers
58 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 ...
3
votes
1answer
58 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 ...
1
vote
1answer
85 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 ...
2
votes
1answer
73 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 ...
1
vote
1answer
99 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
81 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
1answer
70 views
1
vote
2answers
116 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 ...
1
vote
2answers
61 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.
...
-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
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
2answers
153 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
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?
-1
votes
0answers
37 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.
...
1
vote
2answers
96 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
2answers
108 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 ...
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 ...
0
votes
1answer
58 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
59 views
Encrypting a broadcast channel
We're building a data service that is expected to go out through a single "fat pipe" channel. The design requirement says that the data in the channel must be protected by authentication and ...
3
votes
1answer
115 views
Using an MD5 hash as a password
Suppose Alice is using a password prompt that only accepts up to 32 characters for any particular password.
Memorization of long strings of random characters is not one of Alice's strengths, so she ...
1
vote
2answers
80 views
CSPRNG in JavaScript using Audio and Video
I ported GnuPG to Javascript using Emscripten (not released yet).
Now I need a good replacement for /dev/random//dev/urandom.
...
2
votes
1answer
67 views
Why is the discrete log problem easy when the exponent comes from a binomial distribution?
I read in http://epubs.surrey.ac.uk/7219/2/esorics06.pdf that in exponential El Gamal the discrete log problem for recovering $m$ from $g^m$ can be made tractable when $m$ is drawn from a binomial ...
1
vote
2answers
84 views
Why is the following RSA PRNG cryptographically secure?
One requirement states that the generator has to withstand the next-bit test.
Consider the following PRNG, where we calculate next output $x_i$ via the formula
$x_i = x_{i-1}^ e\mod n$.
I can see ...
3
votes
2answers
177 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 ...
0
votes
1answer
105 views
Designing a security system from scratch with a custom protocol, suggestions needed
For the reasons I cannot go into details, I need to design my own protocol and overall security system which will be used to establish secure data exchange between various devices (most notably ...
-3
votes
1answer
68 views
Can someone help with the following hashes? [closed]
Here are a couple of hashes. I feel it should be easy (simple base conversions?) to decode them but I haven't succeeded so far. Can someone help?
...
-5
votes
0answers
57 views
Crypting text cheating wife on iphone [closed]
Wife received text looks like Chinese with boxes
I am new to cheating with adware and crypting
And embedding can I buy a service or app and cut and paste or copy these texts and they are
Sent back ...
1
vote
2answers
93 views
Combining LFSRs for Stream Ciphers: Why do we need high non-linearity?
Linear Feedback Shift Registers (LFSRs) can be excellent (efficient, fast, and with good statistial properties) pseudo-random generators. Many stream ciphers are based on LFSRs and one of the possible ...
4
votes
2answers
94 views
How to do a literature search
How do I do a literature search of the research literature on cryptography? Assume there's some topic in cryptography I'd like to learn more about; how do I search the cryptographic research ...
0
votes
1answer
55 views
Does SRP reduce to DH key echange when shared password is not secret?
I can find JavaScript implementations of SRP (Secure Remote Password protocol), but nothing that inspires confidence for Diffie-Hellmen key exchange. I also have a separate need for SRP later.
I ...
0
votes
2answers
72 views
random number generator 10-side dice alternative
A lot of sites like this one Here, refer to 10-side dice to generate random number for otp. I was thinking about new ways to generate random numbers,letters and passwords. here what I got.
to ...
0
votes
1answer
40 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
...
6
votes
2answers
160 views
Finding hash almost-collisions
A few months ago, XKCD posted a challenge to find a plaintext which hashed (using Skein 1024 1024) to a specified value. Inputs were scored based on the hamming distance between the hash of the ...
-1
votes
1answer
69 views
Cryptography based upon neural networks [closed]
I would like learn about use neural networks in cryptography. Is there any research literature on this subject? What should I do to learn about the subject?
I am taking short course in neural ...
1
vote
1answer
78 views
Security of Salsa20 with some known plaintext?
Basic question- if I'm encoding a bunch of known filetypes with salsa20, will it still be secure if the plaintext header is known?
Assume that a different IV and Key are generated before each file is ...
