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 ...
114
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11answers
14k 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 ...
371
votes
20answers
57k views
XKCD #936: Short complex password, or long dictionary passphrase?
How accurate is this XKCD comic from August 10, 2011?
XKCD 936: Password Strength
I've always been an advocate of long rather than complex passwords, but most security people (at least the ones ...
168
votes
4answers
42k 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 ...
70
votes
21answers
16k views
Lessons learned and misconceptions regarding encryption and cryptology
Cryptology is such a broad subject that even experienced coders will almost always make mistakes the first few times around. However encryption is such an important topic, often we can't afford to ...
35
votes
4answers
11k 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.
...
25
votes
2answers
3k 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, ...
130
votes
9answers
8k 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 ...
43
votes
2answers
5k 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 ...
31
votes
2answers
3k views
Is a rand from /dev/urandom secure for a login key?
Lets say I want to cookie for a user, would simply going to /dev/urandom, generating a 1024 bit string, checking if it already exists (and looping till I get a unique one) suffice? Or should I be ...
23
votes
4answers
1k 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 ...
18
votes
3answers
3k 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 ...
11
votes
4answers
6k 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.
...
13
votes
4answers
1k 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.
...
19
votes
5answers
8k 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 ...
35
votes
4answers
5k 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 ...
25
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2answers
2k 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 ...
15
votes
2answers
494 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 ...
10
votes
6answers
5k 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 ...
24
votes
8answers
1k 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 ...
17
votes
5answers
1k 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. ...
16
votes
3answers
978 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.
...
16
votes
2answers
12k 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, ...
11
votes
2answers
2k 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 ...
23
votes
5answers
2k 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 ...
21
votes
4answers
5k 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 ?
18
votes
6answers
893 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.
...
7
votes
2answers
447 views
Any advantage to securing WiFi with a PSK, other than to keep out unauthorized
As I understand WiFi with a PSK, such as WPA(2)-PSK or WEP, anyone on the same network can decrypt anyone elses packets because everybody has the same key.
In which case, if you are not going to ...
6
votes
1answer
2k views
How can I enumerate all the saved RSA keys in the Microsoft CSP?
I have an application that is creating several keys and storing them in various stores (in this case the Machine store).
How can I enumerate all the keys on a given Windows system?
...
130
votes
8answers
52k 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 ...
43
votes
3answers
16k 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?
25
votes
8answers
2k 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 ...
37
votes
7answers
3k views
Online backup : how could encryption and de-duplication be compatible?
A "soon to enter beta" online backup service, Bitcasa, claims to have both de-duplication (you don't backup something already in the cloud) and client side encryption.
...
23
votes
5answers
1k views
Why is HTTPS not the default protocol?
Why is HTTP still commonly used, instead what I would believe much more secure HTTPS?
19
votes
2answers
4k 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 ...
18
votes
1answer
1k views
Collision rate for different hash algorithms
Is there any collision rate measure for popular hashing algorithms (md5, crc32, sha-*)?
If that depends only from output size, it's quite trivial to measure, but I suppose that depends also of ...
14
votes
5answers
7k 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 ...
12
votes
9answers
656 views
Anybody have additional information on the EMC RSA SecurID compromise?
The Security Advisory Press Release here doesn't have much information, the email that alerted me to this didn't help much more, and unfortunately I heard about the two Thursday evening conference ...
17
votes
8answers
4k 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?
7
votes
5answers
710 views
Save private messages encrypted in database
I'm not sure if this question fits better in StackOverflowSE or CryptoSE but i think this is the right place.
In an online community portal I want to save users' private messages encrypted in a ...
21
votes
3answers
2k views
How does Convergence (CA replacement) prevent its notaries from being MITM'd as well?
I have been looking into Convergence and how it works, but I cant figure out how it is effective against a MITM attack that happens near the target system. My understanding is that Convergence works ...
11
votes
5answers
451 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 ...
12
votes
2answers
2k views
Why is it always `HASH( salt + password )` that we recommend?
Browsing over this site, many forums, online articles, there's always one specific way we're suggesting to store a password hash:
function (salt, pass) {
return ( StrongHash(salt + pass) )
}
But ...
12
votes
5answers
978 views
How should passwords be stored if they must be recoverable?
By "encrypting" passwords you are violating CWE-257: Storing Passwords in a Recoverable Format. But this is exactly what the French government wants. They want to be able to obtain the passwords of ...
11
votes
5answers
8k 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 ...
10
votes
6answers
765 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?) ...
18
votes
4answers
4k views
how long does it take to actually generate rainbow tables?
I've been reading up about rainbow tables as I think they're quite interesting cause they're actually a pretty simple concept.
Anyway, I was wondering, has anyone been involved in actually generating ...
16
votes
1answer
734 views
WPA significantly less secure than WPA2?
I understand at least theoretically WPA2 is more secure than WPA, but in practice does it make any difference which one you use? From what I know there are no known attacks for either except for ...
12
votes
3answers
814 views
What's the mathematical model behind the security claims of symmetric ciphers and digest algorithms?
Why can SHA-1 be considered a secure hash function? That's something I still wonder about.
I understand the concepts of why modern asymmetric algorithms are deemed to be secure. They are founded on ...
11
votes
1answer
670 views
How would I implement “Broadcast Encryption”?
I have a stream that I want to encrypt for broadcast to 10,000 subscribers. I know I should encrypt this data using a symmetric key; and also intend that this symmetric key will be rotated every 30 ...
7
votes
2answers
323 views
Is there a way to negotiate a secret between 2 parties with no prior knowledge?
Is there a way for 2 parties to negotiate a shared secret (for example, a session key) without having a pre-shared knowledge?
SSL does this by using asymmetric encryption. Is there any other way to ...
