2
votes
1answer
392 views

Using “Additional Authenticated Data” as a secondary key

In implementing a cipher in GCM or CCM mode, you are provided the option to add "Additional Authenticated Data" (AAD). This AAD is required for decrypting the cipher text, and seems to be used when ...
2
votes
3answers
146 views

Is it possible to ensure security with zero pre-shared information?

Is it possible to secure a communications channel against both passive (sniffing) and active (injecting / MitM) attackers without either legitimate party knowing any pre-shared information? I know ...
4
votes
2answers
586 views

Is this a correctly formatted PGP session key packet?

RFC 4880 may be full of information, but it can be incredibly vague at times, so im looking for someone who actually knows the answer to this. Given this public key: ...
8
votes
1answer
1k views

S-box design criteria and random sboxes

What are the disadvantages of using random s-boxes? In AES, the s-boxes had to obey certain mathematical rules, which? And why? What security does using hidden s-boxes (GOST) or generating them from ...
1
vote
1answer
347 views

RC4 S-Box and Keystream

I'm studying the RC4 algorithm and I have the following questions: On all questions assume that an expanded (2048-bit) key is used, and that the first 4096 bytes of the KeystreamIm are discarded. ...
1
vote
1answer
816 views

AES-CMAC passes every test except two

i wrote this code: ...
4
votes
1answer
188 views

How to communicate authentication tag for GCM?

I have written some code to do AES in GCM. I currently manually append the tag property to the ciphertext, is this the proper way to communicate the authentication tag?
3
votes
2answers
1k views

Different implementations of SHA1, which one is correct?

I have noticed that different implementations of SHA1 give different results. As I'm currently programming my own SHA1 implementation (in MATLAB / GNU Octave), I wonder which one should I follow? ...
7
votes
2answers
644 views

Is the encryption of a hash a good MAC?

At university we were told that it is a bad idea to implement a MAC by simply concatenating a key with the data to sign and to run it through a hash function (e.g. $s = ...
10
votes
2answers
10k views

Signatures: RSA compared to ECDSA

I'm signing very small messages using RSA, and the signature and public key are added to every message, which requires a lot of space compared to the actual content. I'm considering switching to ...
1
vote
1answer
789 views

AES GCM implementation in c#

I am implementing an AES cipher in GCM mode in c# and have a few questions. My code is based on the code found here for reference. I'll copy in the relevant portions. ...
2
votes
1answer
212 views

Signing 14 bytes of data

for an embedded device I need to sign a 14-byte string and want to verify that string on the device. Since there is already an AES-Library on the device, I thought about using the following scheme: ...
0
votes
1answer
139 views

Combatting traffic shape analysis with spurious packets

I was reading a question about combatting traffic analysis, and a thought occured. If I send random junk messages periodically, would that defeat traffic analysis? The messages would contain some ...
5
votes
1answer
2k views

Padding methods for block ciphers - PKCS7 vs ANSI X.923

I was looking through block cipher padding methods, and found two good candidates: ANSI X.923 - pad with zeros, then a final byte for the padding length, e.g. ...
1
vote
1answer
3k views

Counter Mode in Advanced Encryption Standard(AES) Algorithm

In Advanced Encryption Standard, if I used "Counter Mode", how should I handle the nonce? Should I divide the nonce value into two? For example: I have 128-bit of nonce, should I divide it so I get ...
10
votes
1answer
430 views

Hash function from narrower block cipher operated in CBC-encryption mode?

I am trying to build a public hash function (thus collision-resistant and preimage-resistant, and more generally behaving like a random oracle), with input a message $M$ of fixed size $|M|=m\cdot b$ ...
4
votes
3answers
1k views

Which of these 3 AES 128 symmetric encrypt/decrypt routines is most secure?

I am developing a symmetric en-/decryption routine written in c# for a database containing user-specific, sensitive information. I have narrowed down the implementation to 3 different approaches, ...
3
votes
2answers
302 views

Untraceable communication protocol

I am doing a research about secure communication protocols. I would be interested to know whether a protocol exists such that it grants that the two end-points taking part to the communication cannot ...
2
votes
2answers
118 views

KDF with low-entropy salts

I need to derive a key from a username and a password. These are the only two things I have access to. What I thought is using PBKDF2 with username as the salt and password as the master password. ...
2
votes
3answers
402 views

Entropy of system data - use all and hash, or trim least significant bits?

I'm working on a background entropy collector for key generation that monitors hardware and produces an entropy pool. Here's my list of sources: Mouse position Keyboard timings (i.e. time between ...
2
votes
1answer
439 views

Can we trust digital signatures?

Consider that Alice wants to send a digitally signed message to Bob. Mallory might be able to publish his public key under Alice's name and then impersonate Alice to send a message with an apparently ...
2
votes
1answer
154 views

Format of NONCE in Initialization Vector (IV)

When we talk about a Number used ONCE (NONCE) in Initialization Vector (IV), is it required to use numbers only? Is is possible to use letters or special characters?
17
votes
3answers
362 views

What differentiates a password hash from a cryptographic hash besides speed?

I understand that password hashes like bcrypt have the principal property of taking a long time to run, but I'm wondering what if anything about password hashes make them superior to merely running a ...
2
votes
2answers
338 views

Encryption with private key?

we normally always encrypt by public key and decrypt with private key. If i encrypt with private key, then its still secure as normal PKI ? i mean known-plain-text will not take private key on the ...
3
votes
1answer
396 views

RSA algorithm's license free or paid?

I checked RSA's patent application, which was registered in 1983. As patents don't last more than 20 years, it seems to me it should be free. But my friend said to use RSA I have to buy a license from ...
1
vote
1answer
165 views

Do Quantum Key Distribution and Physical Unclonable Functions combine, and how?

I see there's a project to combine Quantum Key Distribution, Physical Unclonable Functions, and classical crypto, in order to secure a high speed (100Gb/s) optical link. While there does not seem to ...
1
vote
0answers
188 views

Proper formatting of symmetric algorithm secret key

Given this description from RFC 4880 sec 5.1: The value "m" in the above formulas is derived from the session key as follows. First, the session key is prefixed with a one-octet algorithm ...
6
votes
2answers
304 views

Is SSL getting faster because it's getting less secure?

There has been some discussion about it being more practical to use SSL due to advances in hardware. From my understanding, stronger public-key encryption means that both encrypting/decrypting and ...
7
votes
1answer
3k views

why do we need Diffie Hellman?

my question from stackoverflow: http://stackoverflow.com/questions/11374592/why-do-we-need-diffie-hellman Diffie–Hellman offers secure key exchange only if sides are authenticated. for ...
-4
votes
1answer
248 views

Multi layer encryption with ECB mode [closed]

if i use the 2 of the same key with 2 of the same algoritm when encrypting in ECB like when i have 2 blocks of the same color and i encrypt the 2 blocks with the same color the cipher text should not ...
5
votes
1answer
328 views

I need an opinion of encryption method I thought of in High school

First, I'm really not into cryptography, but have some basic knowledge. This was a thought experiment (and later exercise for my programming skills), but even though it was long time ago and I tried ...
5
votes
1answer
1k views

Is this design of client side encryption secure?

I want to build a secure file storage web application. Users should be sure that server doesn't know how to decrypt files so encryption should take place at client side (i.e. in Javascript) and TLS ...
5
votes
2answers
588 views

How many bits can be safely extracted from the BBS generator at each step?

The Blum-Blum-Shub generator is a deterministic Pseudo-Random Bit Generator with security reducible to that of integer factorization. Setup: Secretly chose random primes $P$, $Q$, with $P\equiv ...
24
votes
2answers
5k views

“SHA-256” vs “any 256 bits of SHA-512”, which is more secure?

In terms of security strength, Is there any difference in using the SHA-256 algorithm vs using any random 256 bits of the output of the SHA-512 algorithm? Similarly, what is the security difference ...
-3
votes
1answer
635 views

128-bit Pseudorandom number Generator

Is there any 128-bit pseudorandom number generator available? I tried the Blum Blum Shub Generator, but I can't produce a 128-bit pseudo-random number. Maybe before I produce a 128-bit pseudorandom ...
4
votes
1answer
320 views

Using a derived key for CMAC

Consider the following authenticate-and-encrypt scheme that uses AES-128 in CBC mode for encryption and AES-128 - based CMAC for authentication: Two keys are derived from the master key k (16 byte): ...
2
votes
2answers
299 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)?
2
votes
2answers
253 views

Idea for user/pass hashing to prevent rainbow tables, would it work?

I'm very new to cryptography (and security in general, for that matter), but I had an idea that I'm sure is very flawed, but is worth asking. If a computer user, online account, etc, needs to verify a ...
2
votes
1answer
412 views

Poor man's SSL - is this method as safe as SSL/TLS?

I need to send data between two applications. I've got requirement that says that data should be transmitted using secure protocol such as SSL/TLS. Data is sent using TCP sockets and I don't have ...
4
votes
2answers
3k views

RC4 Keylength Limits

While reading the Wiki page on RC4 I noticed that the key size must be in the range of 40–2,048 bits. Why is that? Is there a reason it can't have a lower or higher length?
3
votes
1answer
214 views

Stream ciphers based on discrete logs

Blum Blum Shub is a stream cipher that is provably reducible to the difficulty of factoring integers. I'm wondering whether there is a similar construction for discrete logs? For example, I could ...
2
votes
1answer
280 views

Vulnerabilities of encrypting data with known regularities

I need to encrypt data that has a pre-defined header and footer structure, and furthermore the data follows pre-defined patterns. The header and footer structure follow a defined structure but cannot ...
4
votes
2answers
165 views

Does a high exponent compensate for a low degree of certainty?

If a RSA certificate is created with a low degree of certainty, does the value of the exponent compensate for this? I'm asking because certain implementations of key generation software hide the ...
1
vote
1answer
160 views

Probability of Repeated Encrypted Block In Output Feedback (OFB) Mode

Is there any probability/chances of repeated encrypted block in Output Feedback (OFB) mode? Is there any existing documentation/studies about that? If it is existing, can you please provide me a link ...
5
votes
2answers
2k views

Replay attack in ECB mode

How do replay attacks work in ECB mode? I found this in Wikipedia: "ECB mode can also make protocols without integrity protection even more susceptible to replay attacks, since each block gets ...
2
votes
2answers
975 views

How to decrypt this RSA-like cipher

Suppose we have a RSA-type Modulus $n = pq$ with $p,q$ prime. We also pick a random public exponent $e$ with $\gcd(e,\varphi(n)) = 1$ and compute the private exponent $d$ with $de \equiv 1 ...
1
vote
1answer
669 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 ...
12
votes
2answers
5k views

Impacts of not using RSA exponent of 65537

This RFC says the RSA Exponent should be 65537. Why is that number recommended and what are the theoretical and practical impacts & risks of making that number higher or lower? What are the ...
1
vote
1answer
1k views

Deciphering a key from XOR encrypted cypher using boolean logic

Assume there's an unencrypted message A, and an encrypted message B. You know that message B was encrypted using a simple XOR method of A with a private key K, resulting in message B. Thus, B = A ⊕ K ...
6
votes
2answers
274 views

Proof of work for standard computers

I'm interested in a proof-of-work system that works well on standard computers without using the GPU. Properties the system should have: Seed based proof-of-work. There is no distinguished ...

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