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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386
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11answers
76k views

How to securely hash passwords?

If I hash passwords before storing them in my database, is that sufficient to prevent them being recovered by anyone? I should point out that this relates only to retrieval directly from the ...
695
votes
22answers
140k views

XKCD #936: Short complex password, or long dictionary passphrase?

How accurate is this XKCD comic from August 10, 2011? I've always been an advocate of long rather than complex passwords, but most security people (at least the ones that I've talked to) are ...
336
votes
4answers
107k views

Do any security experts recommend bcrypt for password storage?

On the surface bcrypt, an 11 year old security algorithm designed for hashing passwords by Niels Provos and David Mazieres, which is based on the initialization function used in the NIST approved ...
96
votes
6answers
37k views

Password Hashing add salt + pepper or is salt enough?

Please Note: I'm aware that the proper method for secure password storage hashing is either scrypt or bcrypt. This question isn't for implementation in actual software, it's for my own understanding. ...
252
votes
13answers
29k views

How is it possible that people observing an HTTPS connection being established wouldn't know how to decrypt it?

I've often heard it said that if you're logging in to a website - a bank, GMail, whatever - via HTTPS, that the information you transmit is safe from snooping by 3rd parties. I've always been a little ...
58
votes
2answers
13k views

Amount of simple operations that is safely out of reach for all humanity?

Cryptographic primitives usually assert some security level given as number of operations to mount an attack. Hash functions, for example, give different security levels for collision attacks, ...
92
votes
3answers
16k views

Is a rand from /dev/urandom secure for a login key?

Lets say I want to create a cookie for a user. Would simply generating a 1024 bit string by using /dev/urandom, and checking if it already exists (looping until I get a unique one) suffice? Or should ...
73
votes
6answers
13k views

Why shouldn't we roll our own?

Why shouldn't we create our own security schemes? I see a lot of questions around here about custom crypto and custom security mechanisms, especially around password hashing. With that in mind, I'm ...
69
votes
8answers
166k views

How to determine what type of encoding/encryption has been used?

Is there a way to find what type of encryption/encoding is being used? For example, I am testing a web application which stores the password in the database in an encrypted format ...
77
votes
2answers
20k views

What are rainbow tables and how are they used?

Where can I find one? Is there a pot of gold at the end? How do I protect against them? From the Area51 proposal This question was IT Security Question of the Week. Read the Sep 09, 2011 blog ...
47
votes
6answers
7k views

How do some sites (e.g. online banks) only ask for specific characters from a password without storing it as plaintext?

I thought How can a system enforce a minimum number of changed characters... would answer my question, but it seems this is a different case. When I sign on to my online banking account, I'm prompted ...
148
votes
8answers
24k views

Why are salted hashes more secure?

I know there are many discussions on salted hashes, and I understand that the purpose is to make it impossible to build a rainbow table of all possible hashes (generally up to 7 characters). My ...
53
votes
5answers
14k views

Why should one not use the same asymmetric key for encryption as they do for signing?

In an answer to a question about RSA and PGP, PulpSpy noted this: It is possible to generate an RSA key pair using GPG (for both encryption and signing -- you should not use the same key for ...
166
votes
8answers
74k views

Why not use larger cipher keys?

RSA Security commonly uses keys of sizes 1024-bit, 2048-bit or even 3072-bit. And most Symmetric algorithms only between 112-bit and 256-bit. I do realize that the current keys are secure enough for ...
91
votes
4answers
21k views

Recommended # of iterations when using PKBDF2-SHA256?

I'm curious if anyone has any advice or points of reference when it comes to determining how many iterations is 'good enough' when using PBKDF2 (specifically with SHA-256). Certainly, 'good enough' is ...
27
votes
5answers
3k 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, ...
43
votes
8answers
5k views

Why is HTTPS not the default protocol?

Why is HTTP still commonly used, instead what I would believe much more secure HTTPS?
26
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 ...
37
votes
3answers
35k views

What is ECDHE-RSA?

What is the difference between ECDHE-RSA and DHE-RSA? I know that DHE-RSA is (in one sentence) Diffie Hellman signed using RSA keys. Where DH is used for forward secrecy and RSA guards against MITM, ...
30
votes
9answers
21k 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?
21
votes
4answers
3k 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 ...
185
votes
3answers
177k views

What's the difference between SSL, TLS, and HTTPS?

I get confused with the terms in this area. What is SSL, TLS, and HTTPS? What are the differences between them?
64
votes
5answers
23k views

Is sending password to user email secure?

How secure is sending passwords through email to a user, since email isn't secured by HTTPS. What is the best way to secure it? Should i use encryption?
36
votes
3answers
9k views

symmetric encryption session keys in SSL/TLS

This question concerns the session send and receive keys used in SSL/TLS protocol. my understanding is that this key uses symmetric encryption (DES, AES, BlowFish, etc.) I'm wondering, if ...
270
votes
7answers
213k views

RSA vs. DSA for SSH authentication keys

When generating SSH authentication keys on a Unix/Linux system with ssh-keygen, you're given the choice of creating a RSA or DSA key pair (using -t type). What is the difference between RSA and DSA ...
25
votes
5answers
24k 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
4answers
50k views

Google Chrome “Your connection to website is encrypted with obsolete cryptography”

Google Chrome is showing new information in the certificate section. Is this a big deal? If so how can I fix it on the server end? EDIT: Thanks for the answers but I'm not skilled in cryptography ...
28
votes
6answers
28k 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 ...
15
votes
4answers
3k views

In what ways does Full or Partial Homomorphic Encryption benefit the cloud?

Can someone explain, in plain English, the practical ways FHE and PHE can be leveraged in the cloud? Some interesting (and confusing) links include this Microsoft Research PDF and this wiki entry. ...
36
votes
2answers
51k views

How to estimate the time needed to crack RSA encryption?

How to estimate the time needed to crack RSA encryption? I mean the time needed to crack Rsa encryption with key length of 1024, 2048, 3072, 4096, 5120, 6144, 5120, 7168, 8192, 9216, 10240, 11264, ...
29
votes
4answers
20k 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 ?
33
votes
6answers
34k 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 ...
30
votes
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 ...
29
votes
3answers
4k 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. ...
12
votes
5answers
22k views

Compute the AES-encryption key given the plaintext and its ciphertext?

I'm tasked with creating database tables in Oracle which contain encrypted strings (i.e., the columns are RAW). The strings are encrypted by the application (using AES, 128-bit key) and stored in ...
66
votes
3answers
72k views

Is Telegram secure?

There is a new WhatsApp-killer application called Telegram. They said that it's open source and that it has a more secure encryption. But they store all the messages in their servers and WhatsApp ...
45
votes
4answers
17k views

What is the use of a client nonce?

After reading Part I of Ross Anderson's book, Security Engineering, and clarifying some topics on Wikipedia, I came across the idea of Client Nonce (cnonce). Ross never mentions it in his book and I'm ...
42
votes
5answers
83k views

Why most people use 256 bit encryption instead of 128 bit?

Isn't 128 bit security enough for most practical applications?
43
votes
2answers
28k views

How secure is Ubuntu's default full-disk encryption?

How secure is the encryption offered by ubuntu (using the disk utility)? What algorithm is used underneath it? If someone could at least provide a link to some documentation or article regarding that ...
40
votes
2answers
5k views

Pre-hash password before applying bcrypt to avoid restricting password length

Good practice is not to unnecessarily restrict password length, so that appropriately-long passphrases (perhaps 35-45 chars for 6/7 dicewords) can be used. (See e.g. Should I have a maximum password ...
26
votes
6answers
11k 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 ...
29
votes
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 ...
32
votes
2answers
12k 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 ...
28
votes
2answers
16k 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?
22
votes
6answers
2k views

Shouldn't GPG key fetching use a secure connection?

If I run this for example: gpg --keyserver hkp://keyserver.ubuntu.com --recv-keys 0xFBB75451 then does the importing occur in a secure way? I mean does it go over only secured connections? (HKP?) ...
12
votes
6answers
8k views

Is PBKDF2-based System.Cryptology.RFC2898DeriveBytes() “better” for Unicode Password hashing than traditional methods?

When is it appropriate to use RFC2898DeriveBytes versus a typical hash? Update I now understand that a KDF is typically used to create a symmetric key for possible use in encrypting a stream. I ...
20
votes
5answers
5k views

What's the practical limit for rainbow-table based bruteforce?

Say we have a hash of a password. The password can be considered to be made of of totally random characters and has a fixed length of N. The hash is SHA1(password+salt), where the salt is of length M. ...
20
votes
6answers
2k views

What are the good use cases for disk encryption?

I've been researching disk/file system encryption, and on the surface it seems like a good idea for a lot of things. But as I dig further, the security it offers seems more mirage like than real. ...
9
votes
3answers
59k views

CryptoWall 3 - how to prevent and how to decrypt?

My father's computer is now infected with CryptoWall 3, according to the link below. http://www.bleepingcomputer.com/virus-removal/cryptowall-ransomware-information#CryptoWall Is there a way to ...
66
votes
7answers
56k views

Certificate based authentication vs Username and Password authentication

What are the advantages and drawbacks of the certificate based authentication over username and password authentication? I know some, but I would appreciate a structured and detailed answer. UPDATE ...