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Questions tagged [cryptography]

Cryptography is the practice and study of logical means used to achieve information confidentiality, integrity and authenticity. It covers, among other things, encryption (making some data unreadable except for those who know a given secret element, called a key), data hashing (in particular for password storage) and digital signatures (provable integrity and authenticity with non-repudiation).

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45
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7answers
40k views

Why AES is not used for secure hashing, instead of SHA-x?

As far as I understand, AES is believed to be extremely secure. (I have read somewhere that it would certainly not be broken in the next 20 years, but I am still not sure if the author was serious.) ...
35
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3answers
10k views

Why do PGP master keys only have a single subkey, and tie certification with signing by default?

After learning more about PGP subkeys and how to split apart the roles of (S)igning, (E)ncryption, (A)uthentication and (C)ertification, I discovered that in most cases(?) a default master key has a ...
56
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17answers
4k views

Can we still provide confidentiality when cryptography is outlawed?

In certain jurisdictions, use of cryptography by the private sector is limited: e.g. there are reports that in the UAE and other countries not all of the encryption capabilities of the BlackBerry are ...
34
votes
1answer
6k views

How does OpenSSL generate a big prime number so fast?

In order to generate a 2048 bit RSA key pair, you need to generate two big prime numbers with 1024 bits length. As far as I know, OpenSSL chooses a random 1024 bit number and starts looking for a ...
23
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7answers
28k views

What are the realistic, and most secure crypto for Symmetric, Asymmetric, Hash, Message Authentication Code ciphers?

I'm interested in updating this two pronged question for 2011: What cryptology is most appropriate for low-powered devices (such as a cellphone), and yet still effective? What cryptology is most ...
46
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1answer
31k views

SSH Key: Ed25519 vs RSA

A lot of people recommend using Ed25519 instead of RSA keys for SSH. The introduction page of Ed25519 (http://ed25519.cr.yp.to/) says: [..] breaking it has similar difficulty to breaking [..] RSA ...
22
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6answers
52k views

What does “key with length of x bits” mean?

I'd like to know what it means to say "the cryptosystem C uses keys with a length of x bits". I do not understand what the bits length means... doesn't it depend on the encoding? The same word encodes ...
70
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4answers
179k views

Is SHA1 better than MD5 only because it generates a hash of 160 bits?

It is well known that SHA1 is recommended more than MD5 for hashing since MD5 is practically broken as lot of collisions have been found. With the birthday attack, it is possible to get a collision ...
22
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1answer
19k views

When to use HMAC alongside AES?

One of my clients wants to provide an URL to each of his customers to register in a system. This URL would contain a query string parameter with some data (e.g. code, email and name) from his clients ...
45
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6answers
4k views

“Real” Salt and “Fake” Salt

During a Q&A period at DEFCON this year, one member of the audience mentioned that we're using "fake salt" when concatenating a random value and a password before hashing. He defined "real salt" ...
24
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4answers
6k views

Computationally simple, lightweight replacement for SSL/TLS

Target hardware is a rather low-powered MCU (ARM Cortex-M3 @72MHz, with just about 64KB SRAM and 256KB flash), so walking the thin line here. My board does have ethernet, and I will eventually get ...
22
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5answers
1k views

What concrete parameters can I change to make my passphrase-protected private gpg key more secure

There are several questions which discuss the resistance of passphrase-protected private gpg keys against brute force attacks. It seems, this kind of discussion could go on forever. Rather than ...
14
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5answers
12k views

Generate a PGP key with more than 4096 bits?

I would like to know if generating a PGP key with a number of bits higher than 4096 is possible and if so how?
31
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4answers
42k views

Whats the difference between MAC vs hash

What is the difference between the two algorithms? One difference that I know of, is that MAC is keyed and hash is not.
27
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7answers
2k views

At what level of abstraction should a developer work with with regards to cryptography?

I have recently came across an old blog post by Jeff Atwood which got me thinking. What could be easier than a EncryptStringForBrowser() method which has security and tamper-resistance built in, ...
27
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4answers
4k views

Flaw in encryption through pseudorandom number stream (from PGP documentation)

I was reading PGP docs and came upon a part written by Phil Zimmermann (PGP's creator) that piqued my curiosity: When I was in college in the early 70s, I devised what I believed was a brilliant ...
30
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2answers
15k views

How big should salt be?

I will be using scrypt to store passwords in my application. As such, I'll be using SHA-256 and Salsa20 crypto primitives (with PBKDF2). Having that in mind, how big salt should I use? Should it be ...
16
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5answers
4k views

The AES Crypt implementation hashes a password 8192 times to generate the key. Is this necessary?

I'm considering encrypting some small files (hundreds of kb apiece) using the AES Crypt reference implementation. Looking at the source, it seems that the encryption key is derived from the IV and the ...
11
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3answers
10k views

How does an SSL server prove its identity?

This document says that a challenge response authentication proves the servers identity. But is a man in the middle attack still possible if the client does not verify domain name ? Please help me ...
11
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4answers
4k views

Tool for public key cryptography where password is the private key?

Is there any free & open source tool for public key cryptography, where the private key is just a chosen password? Here is what I need: I want to make backups every hour using a script I want to ...
17
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8answers
9k views

Are there any “real world” implementations of secret-sharing encryption schemes?

Imagine something like TrueCrypt where user A can decrypt his files, or any 3 of the 10 directors in his organization can decrypt user A's files. As I understand it this is similar to the way the ...
15
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4answers
4k views

Is there a length beyond which increasing password length provides no additional security?

Assuming that the password is stored hashed and salted, and that it is a string of random characters, is there a point where adding to password length doesn't add security? Since the hash will have a ...
15
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5answers
801 views

What is the potential impact of the alleged OpenBSD IPSEC attack?

Recently there is a bit of concern over encryption back doors in IPsec and while the status of this has not been confirmed, I don't know what impact something like this might have. For instance, does ...
15
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2answers
4k views

What are the most common password salting methods?

I learned that the Sun guys used the login name as salt for password hashing. Is this a common approach? What are the most common salt values?
12
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3answers
4k views

How can I mitigate the threat that DPAPick poses to my DPAPI protected data?

The Windows Data Protection API (DPAPI) is the suggested method for storing secrets on Windows systems (such as database passwords required by ASP.Net applications). DPAPick was presented at BlackHat ...
11
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5answers
7k views

Is this RSA/AES combination good?

The team of developers I am part of is trying to develop a safe way to exchange sensitive data between a server and mobile devices. We have come up with the following algorithm: Device generates ...
10
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1answer
5k views

How to choose a stream cipher

Are there high-speed ciphers designed for things like internet streams without sacrificing security? There are so many options that operate in stream mode. How would one choose a cipher?
9
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4answers
3k views

What Partial Homomorphic Encryption implementations exist and how do I leverage them?

It appears that only Partial Homomorphic Encryption(P.H.E.) is practical for modern day (2011) use. However I'm having difficulty locating libraries (FOSS or otherwise) that enable me to leverage ...
9
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2answers
2k views

How the NSA can break trillions of encrypted Web and VPN connections

Based on Diffie-Hellman's negotiation of key exchange, why would it turn out that only a few primes are commonly used? What and who determines the prime? Would it not be safer to use a safe prime? (...
8
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2answers
9k views

Confusing about Ephemeral Diffie-Hellman

1 Does Ephemeral Diffie-Hellman support authentication? Quote from www.rsa.com/products/bsafe/documentation/mesuite21html/dev_guide/group_EPH_DH.html Ephemeral Diffie-Hellman does NOT provide ...
8
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2answers
6k views

In Ephemeral Diffie Hellman Key Exchange - what is actually ephemeral?

Just starting to learn about Diffie-Hellman, and it seems simple enough, but I am struggling to find any resources that explain in an Ephemeral Diffie Hellman Key Exchange, what it is that is actually ...
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3answers
6k views

How would you know a certificate/private key if you extracted it from RAM? Or would you?

Related to, of course, the heartbleed vulnerability, I've been reading the news about the worst case scenario for this attack being the extraction of the SSL private key, because, of course, this ...
4
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1answer
2k views

Is there any functional distributed timestamp server available? If not what about this homebrew solution?

Objective A secure Arrow of Time with unpredictable future behaviour to stop attackers or DDoS BotNets from pre-calculating proof-of-work and other gateway protections for P2P/F2F. A distributed ...
23
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5answers
5k views

Why did TLS 1.3 drop AES-CBC?

I was watching this video about TLS 1.3: "Deploying TLS 1.3: the great, the good and the bad (33c3)" and was somewhat surprised to see that in their effort to provide "fewer, better choices" they ...
22
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4answers
16k views

How quickly can these password schemes really be beaten?

If you use a quick hashing algorithm like MD5 or SHA-1 to hash passwords and you don't use any salt at all, how quickly could one expect a hacker to find my password out? If I use a truly random salt ...
18
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3answers
8k views

Is it safe to use rng-tools on a virtual machine?

I am currently working on an app that needs to create GPG key pairs using the gpg tool. Unfortunately, this tool takes a long time to generate a key pair if there is insufficient entropy/randomness ...
16
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3answers
26k views

Why triple DES used in EDE mode?

Why is triple DES is calculated in encrypt decrypt encrypt mode? Why a decrypt in the middle? And isn't decrypt = encrypt since DES in a symmetric cipher?
16
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5answers
6k views

Multiple CAs signing a single Cert/CSR?

Just saw this suggested on Slashdot So I've seen quite a few people wanting a switch to self-signed certs (who IMO mostly don't understand what making that secure actually involves), and an idea to ...
11
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3answers
2k views

How do poor-quality initialization vectors affect the security of CBC mode?

(If the consensus is that this question belongs on crypto, rather than here, please feel free to [tell me to] migrate it.) From what I have read (looking specifically at AES in Cipher Block Chaining ...
10
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2answers
1k views

Techniques to detect & mitigate Crypto-ransomware?

Crypto ransomware attacks are the latest concerns for our organization, we need to verify if we are adequately protected from them & if affected, what are the generic mitigation measure? How do ...
9
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3answers
2k views

Is it possible to have authentication without state

In order to login to most websites you need a username and password which is often stored in a SQL database. You are storing per-user information that can change, this is state. Can you prove that ...
8
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4answers
8k views

How insecure are PHP's rand functions?

There are some pseudo-random-number generators in PHP: rand(), srand(), mt_rand(), mt_srand(). You can look at their code here. I understand those functions are insecure, but how insecure are they? ...
14
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3answers
5k views

How to exchange RSA public keys safely between two parties?

How to exchange RSA public keys safely between two parties via internet?
13
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5answers
11k views

How can I decrypt data with Java, without hard-coding the key?

I hope this is not a chicken-egg problem or reinventing the wheel but here goes. I have a Java application that needs to access a password protected file (actually during the application startup). The ...
12
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9answers
4k views

Is there any asymmetrically encrypted file system?

Is there a file system providing a directory where everybody can write, but only the directory owner can read the files? In theory it could be done by encrypting using the public key while writing, ...
10
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1answer
745 views

What cryptosystem makes the encrypted text look like random noise?

Suppose one wants to setup a cryptographic protocol in which 2 parties communicate using an encryption scheme that produces encrypted messages indistinguishable from random data (the desired property) ...
6
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1answer
1k views

CryptoLocker master key

I am struggling to understand how it is possible to decrypt files encrypted by the TeslaCrypt ransomware using the master key their creators provided. As far as I know, ransomware encrypts files ...
5
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3answers
1k views

Asymmetric vs symmetric encryption benchmarks

I have found these benchmarks in Crypto++'s site. http://www.cryptopp.com/benchmarks.html But I am, quite honestly, not entirely sure how to interpret them. I am really looking for a set of ...
4
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3answers
20k views

Chrome showing cryptography as 'obsolete' [duplicate]

Similar to this question, Chrome is showing the connection cryptography as obsolete. Opera, IE and Firefox seem perfectly fine with the connection. My guess would be the message authentication is ...
20
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6answers
5k views

Does prepending a salt to the password instead of inserting it in the middle decrease security?

I read somewhere that adding a salt at the beginning of a password before hashing it is a bad idea. Instead, the article claimed it is much more secure to insert it somewhere in the middle of the ...