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 ...

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3answers
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Is Git crowdsourcing cryptographic attacks?

A strong cryptographic hash makes collisions unlikely. Many cryptographic protocols build on that fact. But Git is using SHA-1 hashes as object identifiers. So there are a lot of already computed ...
44
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4answers
3k views

What cryptographic flaw was exploited by Flame, to get its code signed by Microsoft?

Today, Microsoft released a security advisory warning that the "Flame" malware exploited a weakness in a cryptographic algorithm used by Microsoft Terminal Server Licensing Service, and was thereby ...
42
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4answers
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Are salted SHA-256/512 hashes still safe if the hashes and their salts are exposed?

Scenario: a database of hashed and and salted passwords, including salts for each password, is stolen by a malicious user. Passwords are 6-10 chars long and chosen by non-technical users. Can this ...
41
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5answers
33k views

Should RSA public exponent be only in {3, 5, 17, 257 or 65537} due to security considerations?

In my project I'm using the value of public exponent of 4451h. I thought it's safe and ok until I started to use one commercial RSA encryption library. If I use this exponent with this library, it ...
41
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10answers
3k views

Cryptography that looks like ordinary email

I would like to stay out of the automatic filters in place by security agencies and not be accidentally placed on a no-fly list or such. Say I'm having a political debate with a friend about democracy ...
40
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7answers
3k 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" ...
39
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7answers
5k views

Exploiting MD5 vulnerability in this PHP form?

I've been practicing in security-related topics and I came upon this problem which I don't understand at all. You receive a form with one input named pass, and this is the code you need to bypass: &...
39
votes
4answers
31k views

How does PGP differ from S/MIME?

Is S/MIME an abstracted system for general MIME type encryption, whereas PGP is more for email? Why would I want to choose one over the other, or can I use both at the same time?
38
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9answers
28k views

Feeding /dev/random entropy pool?

Which way of additionally feeding /dev/random entropy pool would you suggest for producing random passwords? Or, is there maybe a better way to locally create fully random passwords?
38
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6answers
45k views

Asymmetric vs Symmetric Encryption

I am currently taking a principles of information security class. While talking about different encryption methods a large number of my classmates seem to believe that Asymmetric Encryption is better (...
38
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3answers
26k views

What are the risks of self signing a certificate for SSL

Let's say I sign a SSL certificate for myself, and I'm not using a certified CA. What are the risks and/or threats of doing it?
37
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2answers
4k views

How can it be easy to write but “impossible” to extract the private key from a crypto token?

A number of crypto-dongles make the claim that it is impossible to extract the stored private key once written. Yubico: The YubiKey AES Key information can never be extracted from a YubiKey ...
36
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15answers
7k views

Why do people think that this is bad way to hash passwords?

Well, please tell me, what's wrong with this code: $password = "hello"; $password = md5($password); for($i=1;$i<20;$i++){ $password = md5($password); } It's exactly the same as this one: ...
36
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7answers
22k views

Where can I learn cryptography/cryptanalysis the hard way, without going to school ? Any good book?

I'm not so bad at mathematics: I know what are p-list and p-combinations, I know matrix algebra, I know what a XOR is, I know how to tell if number is a prime, etc: I'm not the programmer who hates ...
36
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2answers
69k views

Security comparsion of 3DES and AES

Which one is more secure and least possible to be broken through cryptanalysis AES or 3DES (no matter performance)? I need to use encryption for my projects to store and secure sensitive information ...
35
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7answers
11k views

Is salting a hash really as secure as common knowledge implies?

(I did search on this topic, but I found no complete question/answer that addressed it, or even good portions of questions that might be relevant.) I'm implementing a salt function for user passwords ...
35
votes
8answers
4k views

Find matching phone numbers without actually knowing them

We have a mobile app that, given two users, needs to let them see what common contacts they have based on their phone numbers. How can we do this in a cryptographically secure way and respecting the ...
35
votes
5answers
19k 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.) ...
34
votes
2answers
9k views

Criteria for Selecting an HSM

A very sensitive application has to protect several different forms of data, such as passwords, credit cards, and secret documents - and encryption keys, of course. As an alternative to developing a ...
34
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2answers
14k views

HMAC - Why not HMAC for password storage?

Nota bene: I'm aware that the good answer to secure password storage is either scrypt or bcrypt. This question isn't for implementation in actual software, it's for my own understanding. Let's say ...
33
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4answers
6k views

How does a hacker know how many times a password was hashed?

I've been reading a lot of questions about security and hash functions on this site and others. I am not an expert, just a curious mind and in my understanding the more iterations used to hash a ...
33
votes
2answers
2k views

Are URLs viewed during HTTPS transactions to one or more websites from a single IP distinguishable?

For example, say the following are HTTPS URLs to two websites by one IP over 5 mins: "A.com/1", "A.com/2", "A.com/3", "B.com/1", "B.com/2". Would monitoring of packets reveal: nothing, reveal only ...
33
votes
5answers
9k views

What does Amazon's S3 Server-side encryption protect against?

Amazon's S3 storage service offers server-side encryption of objects, automatically managed for the user (Amazon's Documentation). It's easy to enable so I'm thinking "why not?", but what kind of ...
33
votes
2answers
2k views

How to start writing crypto software [closed]

This is just an academic question, I do not intend to write my own crypto software. Every time someone asks the question “How do I write my own Crypto?” the answer is don't. I'm currently studying ...
31
votes
3answers
5k views

Is there any advantage to splitting a password?

I've been reading about the LANMAN (LM) hash and I'm curious about a particular part of the algorithm. The LM hash is computed as follows: The user’s ASCII password is converted to uppercase. ...
31
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8answers
3k views

If someone breaks encryption, how do they know they're successful?

Let's say I have a file containing a random bunch of bits and then I encrypt it using some modern algorithm (Blowfish, AES, or whatever). If someone captures the file and mounts a brute force attack ...
30
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8answers
5k views

Why would salt not have prevented LinkedIn passwords from getting cracked?

In this interview posted on Krebs on Security, this question was asked and answered: BK: I’ve heard people say, you know this probably would not have happened if LinkedIn and others had salted ...
30
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5answers
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Where to get an SSL certificate for personal website?

I would like to use https to login to my personal webpage (which is on shared hosting). So I went over to google and started searching for sollutions. Eventualy I found out that I need an SSL ...
29
votes
4answers
26k views

How to achieve non-repudiation?

If I have a message that I need to send to another person, how do I achieve non repudiation ? Is digitally signing the message sufficient ?
29
votes
5answers
4k views

How valuable is secrecy of an algorithm?

On the surface, the inadvisability of security through obscurity is directly at odds with the concept of shared secrets (i.e. "passwords"). Which is to say: if secrecy around passwords is valuable, ...
29
votes
6answers
11k views

Is AES encrypting a password with itself more secure than SHA1?

This isn't really a practical question, but more a question of curiosity. I heard a CS professor recommend stepping up from md5ing passwords not to SHA1, but to AES encrypting the password using ...
29
votes
2answers
3k views

What actually happens in “low voltage fault attacks”

I understand they are an attack on crypto algorithms as implemented on various processors, but how do they work? The online papers are too complex for me to understand.
29
votes
4answers
6k views

How can PrivateSky not see your data?

PrivateSky is a website that promises encrypted "cloud-like" secure information exchange. They promise that except the sender and receiver, nobody can see your data. After testing it yesterday, I do ...
29
votes
3answers
8k views

When changing a PGP passphrase, does it only affect the private key?

I am beginning to use GPG for email encryption. If I use gpg --edit-key [keyID] to change the passphrase, what files will this affect? Will it only affect my private key, and thus I only need to ...
29
votes
6answers
37k views

Most secure password hash algorithm(s)?

What is/are currently the most cryptographically secure hashing algorithm(s)? (available in PHP) Speed is irrelevant, because I'm iterating the hash over a fixed time (rather than a fixed number of ...
29
votes
3answers
17k views

Which SSL/TLS ciphers can be considered secure?

The OpenSSL website provides a long list of different ciphers available for SSL and TLS. My question is, which of those ciphers can be considered secure nowadays. I am especially interested in HTTPS, ...
29
votes
4answers
3k views

How to encrypt in PHP, properly?

How do I encrypt data in PHP, properly, using symmetric-key encryption? I have a message M and a secret S. I'm looking for a solution that uses cryptography properly without making any of the usual ...
28
votes
7answers
13k views

Could SQRL really be as secure as they say?

I just came across https://www.grc.com/sqrl/sqrl.htm With Secure QR Login, your phone snaps the QR code displayed on a website's login page . . . . and YOU are securely logged in. This ...
28
votes
2answers
11k views

What is the difference between a Hash Function and a Cryptographic Hash Function?

I mean, is it just a matter of "how difficult is it to reverse the function with the current technology"? Or is there a mathematical concept or property that makes them different? If it is a matter ...
27
votes
2answers
22k views

Why are GPUs so good at cracking passwords?

What is it about GPUs that lets them crack passwords so quickly? It seems like the driving force behind adopting good key-derivation functions for passwords (bcrpyt, PBKDF2, scrypt) instead of ...
27
votes
5answers
29k views

What ciphers should I use in my web server after I configure my SSL certificate?

There are many great questions that ask what is the best certificate to use for a website; but once the certificate is purchased, there is also the possibility to choose or edit the Cipher list. ...
27
votes
8answers
13k views

Do secure phone lines exist?

I could be out of context here about security, but , I would like to know if phone lines or phone calls over VOIP could be made secure . I know that Skype and other VOIP service providers have to ...
27
votes
2answers
1k views

Does versioning an encrypted file make it less secure?

Suppose I use KeePassX as a password manager, and I store the kdb file in Sparkleshare folder as a way for backing up and syncing with multiple devices. The kdb file in itself would be encrypted, but ...
27
votes
1answer
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How should API keys be generated?

I want to make sure requests can't be forged and sent on to my server. In order to do this I need to generate an API key per user on my system. The purpose of the key will be to sign requests on the ...
26
votes
8answers
3k views

Why is password hashing considered so important?

After reading this article, I can see the benefits of password hashing as a second layer of defence, in the event of an intruder gaining access to a password database. What I still don't understand is ...
26
votes
12answers
5k views

Can a file contain its md5sum inside it?

Just wondering if it is possible to create a file which has its md5sum inside it along with other contents too.
26
votes
4answers
39k views

how digital signature verification process works

I am not able to understand that how the digital signature is verified. I know that digital signature will be attached to the message and sent by sender to receiver. then receiver uses the public key ...
25
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7answers
9k views

Why don't people hash and salt usernames before storing them

Everyone knows that if they have a system that requires a password to log in, they should be storing a hashed & salted copy of the required password, rather than the password in plaintext. What I ...
25
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5answers
5k views

Never spell a word the same way twice?

A long time ago I was reading about Renaissance-era ciphers and I remembered this quote: David Kahn, author of The Codebreakers, quotes Giovanni Battista Porta who published, in 1563, a famous ...
25
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4answers
4k views

What to transfer? Password or its hash?

Let's say in my database I store passwords hashed with salt with a fairly expensive hash (scrypt, 1000 rounds of SHA2, whatever). Upon login, what should I transfer over the network and why? Password ...