# All Questions

218 views

### Is there a client-side program to cryptography a HTML page and decode if correct password is writen? [closed]

I want to know if there is an easy way to do this: create a complete HTML page cryptography the text content (image is not important) ask user some password check the password with a cryptographed ...
332 views

### Strength of RSA with OAEP

In our current system we use an encryption solution based on RSA with OAEP padding. Key size is optional but default 2048. What is the general strength of RSA with OAEP? Are there know attacks that ...
104 views

### Unique assignment of X.509 certificate to each client

I'm trying to implement a short scale electronic voting application in a domain comprised of no more than 100 clients. System administrator is able to create new election instances and each client is ...
39 views

### Question about key verification

I am studying for network security exam. And in the slide about Key Management, under a heading Key Verification I see this: Key Verification Almost all cryptographic algorithms have some weak keys ...
153 views

### How much (home PC) CPU time is required to generate a prime number of a given size?

How much CPU time is required on a typical home computer to generate a prime number of size 100 bit, 200 bit , 512 bit and 1024 bit using given random bits of the respective sizes? Please note that ...
344 views

### Remove padding (CBC) from decrypted text [closed]

I have a bit problem with padding. Everything goes fine when I encrypt the text BUT when I decrypt I see some extra characters. Sometime's one character sometimes more and I dont know how to remove ...
100 views

### Possible to use an accumulator to “license” or restrict the qty of certificates being used?

Suppose in a future version of x509 PKI, it is possible to limit the quantity of certificates being used, what would that look like? Here is a concept that won't work in the real world, but ...
266 views

### Problem with implementing DES in python

i'm implementing DES in python and i've stumbled upon a problem i can't really find the problem, after debugging it i narrowed it down to this function, can anyone tell me if i'm implementing the DES ...
155 views

### Which block cipher mode does the experts use? [closed]

I want to know which "block cipher mode of operation" does the experts use? I don't want to use ECB or CBC because add padding and padding mess up my code. So which one does the experts use. /Thanks
551 views

### How secure is file header encryption for large files?

I'm having trouble location information about whether or not encrypting a file's header is good enough. The files in question are media files that range in size from 500mb to 4GB. If I had no ...
182 views

### Montgomery Algorithm

I'm trying to undestand how it works and how to implement the algo described in this paper. The paper shows a methods to compute a modular multiplication where it is used multiplier with a resolution ...
209 views

### subgroup of quadratic residue

if a number is said to be a subgroup of a quadratic residue of Z∗p, can I affirm that it is a generator of a cyclic group ? ie, say i am looking for a number which is an element of order q in Z*p, ...
163 views

### Discrepancy with reported key size for EDE ciphers in Qualys SSL Labs

The following two cipher suites were reported by Qualys SSL Labs as being 112-bit: SSL_CK_DES_192_EDE3_CBC_WITH_MD5 TLS_RSA_WITH_3DES_EDE_CBC_SHA However, all other references I can find say that ...
823 views

### What is the algorithm behind PasswordDeriveBytes?

Microsoft has created an implementation of PBKDF1 in the PasswordDeriveBytes class. It can however generate more bytes than PBKDF1, which is limited to the number ...
138 views

### Are there any known inverse hash lookups for the zero string?

Just wondering, are there any known inverse hashes / hash lookups in common hashes (md5, sha1, sha2, etc.) for the zero string hash value? (i.e. bytes 0x00 00 00 00 00 ...) Or more specifically, for ...
158 views

### Entropy in relation to computer security [closed]

I am going over some lecture notes and my lecturer is off sick, so not sure where to turn. There is this equation that I cannot understand as it's given with a couple of examples. I was hoping ...
503 views

### Key derivation of public key without knowledge of private key

I'm looking for a convenient way to share a set of public keys across multiple services, while preserving privacy by preventing these services from tying the identity of these public key sets together ...
435 views

284 views

### Random Galois fields

Note: I have now answered this by my own research and can generate random fields up to G(2^9) in reasonable time. I would need to find more speedups for larger fields. At this time G(2^8) takes a few ...
205 views

### Split 32-bit LFSR into two 16-bit LFSR which xor to same sequence [duplicate]

Today I was thinking about exactly this. Is it possible, for a 32-bit LFSR e.g. ...
62 views

### Many Time Attack [closed]

How i can XOR these two cipher texts encrypted by using same key First ...
135 views

### Why are cryptographically secure hashes required for digital signing (RSA or DSA)?

I know that a cryptographically secure hashing algorithm is required for proper message signing (SHA-1, or I think SHA-2 is the current suggested algorithm). However, why does the hashing algorithm ...
108 views

### Public key encryption [duplicate]

I am not getting whole idea behind Public Key Encryption technique. As according to fact, public key encryption method uses two keys a public key known to everyone private key known only to recipient ...
370 views

### Deduplication: Encrypting the SHA-256 hash of a file chunk

I'm designing a data storage system that should be both able to deduplicate data that share the same encryption key, and be reasonably secure. I know that this kind of encryption quality can be ...
415 views

### Sophie Germain primes and safe primes

I am trying to find a list or table of safe prime numbers i.e. the ones that are based on the Sophie Germain primes i.e. $N = 2p + 1$ where $p$ is also prime. All I found till now is this database. ...
134 views

### Loss of data due to encryption

Could any kind of encryption method (AES, etc.) lead to data loss like in lossy compression? I'm interested if data (lossy compressed, lossless compressed, uncompressed) that is encrypted and ...
119 views

### Interested in learning cryptography [duplicate]

I'm interested in learning cryptography outside the university(studying civil engineering). I was always interested in computer sciences and programing and in mathematics. I always try to program ...
307 views

### Share encrypted files without giving master key

Imagine I have four files I want to encrypt. I have master key, and from that master key I derive four keys, one for each file: ...
596 views

### Encryption for a short packet size

I have an 8051 microcontroller with a radio that can send packets with up to 32 bytes and I want to have the messages encrypted. It is a sensor network so I really only want to send one packet per ...
250 views

### Difference between statistical PRNG and cryptographic PRNG? [duplicate]

What's the difference between a statistical pseudorandom number generator (PRNG) and a cryptographic-strength PRNG? I've seen a lot of PRNGs that are proposed for statistical uses -- e.g., ...
182 views

### NTRU key generation

I've been experimenting with an NTRU open-source C implementation here I've noticed something (potentionally) strange with a certain set of params: NTRU_EES1087EP2 (defined here). When generating ...
459 views

### How many bits of entropy would I get from 300 coin tosses? [closed]

Bonus question, what is the formula to calculate this?
157 views

### What is the keyspace of ROT-13?

Today I was having a discussion with my cryptography lecturer about the keyspace of a ROT-13 cipher. He argues that the keyspace is 0 because it doesn't have a key. Could anyone explain to me why the ...
127 views

### Is adaptive security the same as full security?

This question contains a great answer about adaptive security, but I haven't yet found a proper definition what full security is. Does a stronger security than adaptive security exist or are the two ...
2k views

### Why is the private key generated first in public key crypto?

I'm still new to public key crypto. I'm trying to understand how it is that the private key is generated first in public key crypto? I would have expected the private and public key to be generated at ...
427 views

### How to roll my own hardware RNG?

I am considering building a hardware RNG myself using cheap parts. Is this a good idea and safe enough? Random sources: amplified Zener noise from one randomly chosen ...
106 views

### Analyzing security flaws of cipher

I know using homebrew encryption can be very dangerous as it is very likely to have many flaws in its design. The following concept is just for learning purpose in case anybody is getting red flags ...
121 views

### Is my method symmetric encryption?

To obfuscate data I made up this method on the spot without planning since the goal wasn't real encryption. At first I though this cannot be real encryption but after revisiting the code and reading ...
355 views

### Performance bottlenecks in Paillier encryption

I'm implementing Paillier encryption and I'd like some recommendations about improving its performance. Firstly, I have to note the following: I have already set g=1+n to get rid of one ...
184 views

### Transforming a key into a seed with the most entropy

I'm making a very simple encrypter in C# which is basically a Stream cipher. The user enters a key(password), converted to a seed for a pseudo-random generator, and the pseudo-random generator ...
591 views

### How to calculate AES logarithm table?

I would like to know how to find multiplicative inverses in $\mathrm{GF}(2^8)$. I know how to multiply two elements of $\mathrm{GF}(2^8)$ (for example, I know that ...
225 views

### What is a good way to demonstrate elliptic curve cryptography?

For school (high school) I am writing an essay on elliptic curve cryptography. The assignment needs to include a practical part, so I decided to write a Python class for elliptic curves. This class is ...
2k views

### How does ECDH arrive on a shared secret?

I read a brilliant, three part article on Elliptic Curve cryptography (one, two, three). It was able to explain Elliptic Curves to me in a way that didn't require a math degree to understand. The ...
288 views

### Why are there no MACs inspired by block cipher modes other than CBC and CFB?

I've been studying message authentication codes and I was wondering why a MAC can only be produced with AES in CBC and CFB mode and why not the other modes such as ECB, OFB and counter. Why are CBC ...
216 views

### How are calculated numbers in AES S-box?

I have a problem calculating the 0x02 value of the AES S-Box. I followed the steps descibed in “How are the AES S-Boxes calculated?”, but my answer is not correct. ...
282 views

### RSA - Why should we sign hash rather than raw content? [duplicate]

Apart from obvious performance considerations, is there any mathematical or crypto reasons that imply that we sign a hash rather than a raw content ? I read that it was because the hash must fit in ...
Definition: (The generalized Diffie-Hellman problem) Let $n=pq$ for two large primes $p,q$. Given $x, x^a, x^b,n$, find $x^{ab}\pmod{n}$. (1) Is there a known reduction from the GDH problem to ...