# All Questions

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### System parameters in identity-based encryption

In IBE schemes, the system parameters are $(q, \mathbb{G}, F, \hat{e}, P, Q, T, H_1)$. I don't know $\hat{e}$. For example, in type A pairing… ...
207 views

### Are there any practical attacks that create a printable chosen prefix MD5 collision?

I would like to create two ASCII text messages with the same MD5. Is this possible? If not, is there a similar but less strict attack that could work? Or to rephrase my last question: what are the ...
27 views

### How to vary bit length of prime numbers in RSA by using MATLAB? [closed]

Please Can any one Tell me how to vary bit length of prime numbers of RSA cryptography algorithm in MATLAB.When i am considering more then 16 bit length of prime numbers Its not working. So can any ...
54 views

### what is meaning of operator “ := ” in cryptography?

I've seen := used in several cryptography papers where the this symbol has been used instead of assignment operator ($\leftarrow$ ) or equal sign (=), but never with an accompanying explanation. ...
44 views

### Are collision-resistant hash functions even possible? [see description] [duplicate]

Surely there can be no real collision resistant Hash function since hash values are of finite size which means there are finitely many of them, but there are an infinite number of messages we could ...
9k views

### What are preimage resistance and collision resistance, and how can the lack thereof be exploited?

What is "preimage resistance", and how can the lack thereof be exploited? How is this different from collision resistance, and are there any known preimage attacks that would be considered feasible?
39 views

### signature, hashing schemes

I have 20 friends. we create message(s) (1...i) and tar them up with a file messages.hashes(1..i). We sign these tars with our ...
57 views

### Is a PRF applied to a secure MAC also a secure MAC?

Suppose I apply a PRF to a secure MAC. Do I still have a secure MAC?
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### Find SHA256(secret||data) using SHA256(secret) and data

I need to find the SHA256 hash of s string like this: "part1-part2". I know the SHA256(part1), length of part1 and I know part2, but I don't know what is the contents of part1. Is there any chance I ...
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### What is transaction capacity of a POS using 3DES DUKPT?

I am looking for the transaction capacity of a Point-Of-Sale device using 3DES DUKPT. Once all keys derived from the future key set are exhausted (1M or 500K?), how will the POS be reloaded with a new ...
7k views

### AES encryption using a Diffie-Hellman key exchange

I have two systems which need to encrypt their communication by AES-128. The key for the AES encryption should be exchanged with the Diffie-Hellman (DH) algorithm. Now, I've read about DH and got a ...
98 views

### AES implementation to encrypt files

I'm making a small python program to encrypt an arbitrary text file. Currently I have a file to store passwords (hashed values), so nothing stored in plaintext. The user enters the command line ...
65 views

### SHA256(RsaPrivateKey) == AES key?

I have an RSA private key (more specifically, an SSH key in Putty format, 4096bit) and want to use its SHA256 hash as an AES256 key, instead of using an independent newly generated AES key. Are ...
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### Is OCB the state of the art in authenticated encryption modes of operation for block ciphers?

OCB mode seems to represent the state of the art in authenticated encryption modes, largely due to its speed – it is faster than GCM even when GCM has hardware support. Its only drawbacks seem ...
65 views

### Exploiting XOR one-time-pads with dictionary length that isn't a power of 2

I realized that if the key is chosen randomly from a range that isn't a power of 2, the one-time-pad leaks information about the plaintext. For example, if the alphabet was the first 20 naturals, ...
33 views

### Why hash function are used in digital signatures? [duplicate]

In the lectures I see, hash functions are always used when we want to sign a document $d$. My question is why they are used in digital signatures? Maybe, because it is more easy and fast to calculate ...
53 views

### How to prove that an integer is hard to factorize when sampled from a known distribution

Suppose that an $n$-bit integer $c$ has been randomly drawn from a distribution $\chi$, whose description is known. Is there a general method to check if this particular sampling helps factorize $n$? ...
29 views

### Encrypt file using pycrypto RSA from python [closed]

Basically I am writing a program that needs to have basic encryption for storing some program parameters in a config file. The program is run under linux debian. Since sudoers can modify the config ...
34 views

### Benchmarks for second round CAESAR competitors

I'm interested in how the second round CAESAR competitors stack up in terms of software performance against each other and against chacha20-poly1305 with both small and large messages. Sadly the only ...
27 views

### Can multi-prime RSA be used to create an abuse-resistant lawful interception mechanism?

New to site so this may have been asked before: Can multi-prime RSA, i.e. where N is product of three or more distinct primes, be used for secure communication while allowing distinct authoritative ...
59 views

### GCM: use the same key:IV pair to encrypt file and filename

Using Java, I wrote a piece of code that encrypts a given file with AES in GCM mode of operation. So far nothing uncommon. Now I would also like to encrypt the filename, in the following way: ...
20 views

### Crypto lib that use files instead of passphrase

I would like to program an application to allow people to encrypt files without using a password or pass-phrase but an arbitrary long file. I'm searching for a library that allows me to safely create ...
37 views

### Attacks on schemes based on elliptic curves when the transmitted points are not on the curve

Some elliptic curve schemes require to send a curve point during the normal execution of the protocol. For example, ElGamal encryption and ElGamal signature require this. On the other hand, ECDSA does ...
27 views

### Steps to encrypt endorsements to a petition

I plan to circulate a petition, asking people to support it. This petition will reach a senior government official. In regular circumstances, people would support such petitions by writing their ...
104 views

I'm trying to reverse engineer a key exchange protocol which is based on the Diffie-Hellman key exchange scheme and faced with the following problem: Let $g$ be the generator, $m$ the modulus. Alice ...
456 views