529
votes
11answers
112k 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 database,...
715
votes
3answers
366k views

How does SSL/TLS work?

How does SSL work? I just realised we don't actually have a definitive answer here, and it's something worth covering. I'd like to see details in terms of: A high level description of the protocol....
841
votes
23answers
168k 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 ...
104
votes
5answers
8k views

How do I deal with a compromised server?

I suspect that one or more of my servers is compromised by a hacker, virus, or other mechanism: What are my first steps? When I arrive on site should I disconnect the server, preserve "evidence", ...
400
votes
5answers
138k 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
39k 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 ...
298
votes
8answers
57k views

How to store salt?

Nowadays, if we expect to store user password securely, we need at least do the following thing $pwd=hash(hash($password) + salt) then store $pwd in your system instead of the real password. I have ...
80
votes
3answers
20k 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, ...
124
votes
6answers
47k 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. ...
118
votes
8answers
23k 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 ...
112
votes
9answers
78k views

How secure are virtual machines really? False sense of security?

I was reading this CompTIA Security+ SYO-201 book, and the author David Prowse claims that: Whichever VM you select, the VM cannot cross the software boundaries set in place. For example, a ...
293
votes
13answers
37k 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 ...
88
votes
8answers
227k 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 (WeJcFMQ/8+8QJ/w0hHh+...
147
votes
5answers
103k views

What is certificate pinning?

I'm superficially familiar with SSL and what certs do. Recently I saw some discussion on cert pinning but there wasn't a definition. A DDG search didn't turn up anything useful. What is certificate ...
354
votes
11answers
44k views

Is my developer's home-brew password security right or wrong, and why?

A developer, let's call him 'Dave', insists on using home-brew scripts for password security. See Dave's proposal below. His team spent months adopting an industry standard protocol using Bcrypt. ...
436
votes
22answers
93k views

How does changing your password every 90 days increase security?

Where I work I'm forced to change my password every 90 days. This security measure has been in place in many organizations for as long as I can remember. Is there a specific security vulnerability ...
126
votes
3answers
22k 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 ...
63
votes
8answers
17k views

How can I reliably erase all information on a hard drive?

As storage technologies change over time, using different encodings and remappings to deal with sector errors, the best way to permanently erase/wipe/shred data changes also. Methods for flash drives ...
95
votes
17answers
15k views

Does an established SSL connection mean a line is really secure?

From the view of somebody offering a web application, when somebody connects with SSL (https) to our service and submits the correct authentication data, is it safe to transmit all sensitive data over ...
68
votes
13answers
22k views

What are the pros and cons of site wide SSL (https)?

What are the pros and cons of encrypting all HTTP traffic for the whole site through SSL, as opposed to SSL on just the login page?
34
votes
6answers
22k views

Differences between using Tor browser and VPN

I can't quite figure out the differences between using the Tor browser and using a VPN (like concretely proXPN). From what I understand the idea is the same, that they both hide the IP address. The ...
175
votes
8answers
39k views

Why are salted hashes more secure for password storage?

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 ...
86
votes
6answers
69k views

Does https prevent man in the middle attacks by proxy server?

There is a desktop client A connecting to website W in a https connection A --> W Somehow between A and W, there is a proxy G. A --> G --> W In this case, will G be able to get the ...
68
votes
12answers
9k views

How feasible is it for a CA to be hacked? Which default trusted root certificates should I remove?

This question has been revised & clarified significantly since the original version. If we look at each trusted certificate in my Trusted Root store, how much should I trust them? What factors ...
41
votes
6answers
18k views

https security - should password be hashed server-side or client-side?

I am building a web application which requires users to login. All communication goes through https. I am using bcrypt to hash passwords. I am facing a dilemma - I used to think it is safer to make a ...
243
votes
3answers
56k views

CRIME - How to beat the BEAST successor?

With the advent of CRIME, BEAST's successor, what possible protection is available for an individual and/or system owner in order to protect themselves and their users against this new attack on TLS?
62
votes
4answers
37k views

Why is writing zeros (or random data) over a hard drive multiple times better than just doing it once?

Lots of different programs, such as Darik's Boot and Nuke, let you write over a hard drive multiple times under the guise of it being more secure than just doing it once. Why?
471
votes
14answers
81k views

What technical reasons are there to have low maximum password lengths?

I have always wondered why so many websites have very firm restrictions on password length (exactly 8 characters, up to 8 characters, etc). These tend to be banks or other sites where I actually care ...
91
votes
2answers
32k 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 ...
93
votes
6answers
17k views

How much can I trust Tor?

How much can I depend on Tor for anonymity? Is it completely secure? My usage is limited to accessing Twitter and Wordpress. I am a political activist from India and I do not enjoy the freedom of ...
97
votes
11answers
8k views

How do you explain the necessity of “nuke it from orbit” to management and users?

When a machine has been infected with malware, most of us here immediately identify the appropriate action as "nuke it from orbit" - i.e. wipe the system and start over. Unfortunately, this is often ...
50
votes
4answers
7k views

Are there DRM techniques to effectively prevent pirating?

A question on Skeptics.SE asks whether current DRM techniques effectively prevent pirating: Is DRM effective? The question for IT Security is: Can DRM be made effective, and are there any examples? ...
60
votes
6answers
25k views

What techniques do advanced firewalls use to protect againt DoS/DDoS?

It is hard to protect a server against Denial of Service attacks, DoS/DDoS. The two simple ways I can think of is to use a server with much resources (e.g. CPU and memory), and to build the server ...
50
votes
6answers
8k 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 ...
78
votes
9answers
17k views

Hardening Linux Server

We have already had questions on here about Hardening Apache, Hardening PHP and Securing SSH. To continue this trend I am interested in what steps people take to harden Linux servers. As in what ...
75
votes
4answers
12k views

Can anybody explain XSS? [closed]

I work programming Enterprise Java applications and do very little web development in 2002. I'm interested in security and like to read articles about it. However, I never fully understand how XSS ...
39
votes
2answers
32k views

Where to store a key for encryption?

I am looking for a way to store a key used for password encryption. I am using a MySQL database which would store a user name and a password encrypted with AES_ENCRYPT(str,key_str). Where can I safely ...
49
votes
9answers
42k views

Can my company see what HTTPS sites I went to?

At work my company uses internet monitoring software (websense). I know if I visit a https ssl-encrypted site (such as https://secure.logmein.com) they can't see what I'm doing on the site since all ...
72
votes
3answers
33k views

What are the career paths in the computer security field?

What sorts of jobs are there, in which organizations, with what sorts of day-to-day responsibilities? What areas are good for folks coming out of school, vs what are good 2nd careers for experienced ...
44
votes
6answers
6k views

How to disclose a security vulnerability in an ethical fashion?

How to disclose a security vulnerability in an ethical way? I've heard there are various schools of thought on this topic. I'd like to know the pros/cons of each.
52
votes
3answers
22k views

Is it enough to only wipe a flash drive once?

According to the documentation for the "diskscrb" command for wiping conventional hard drives: http://www.forensics-intl.com/diskscrb.html "Conforms to and exceeds the Government Standard set ...
67
votes
5answers
20k 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 both)....
66
votes
6answers
43k views

Is there a short command to test if my server is secure against the shellshock bash bug?

I did apt-get update; apt-get upgrade -y on all systems I'm running. I'm not sure if my /etc/apt/sources.list is good enough on all of these systems. I would like to quickly check each system again, ...
42
votes
6answers
184k views

If someone hacks my wi-fi password, what can they see and how?

If someone knows my wifi password (be it WEP or WPA) what can they see? Do they just see URLs I visit, or can they see everything in my browser, or even everything I do on my computer? Does using ...
34
votes
6answers
67k views

Can wiped SSD data be recovered?

I was reading another post on destroying IDE drives, and how you could remove data, wipe it, or just destroy the drive. The removed data would still be there in some state, although not easily ...
35
votes
8answers
28k views

Is making a clean install enough to remove potential malware?

Is formatting the disk and reinstalling the system from scratch (to Ubuntu) enough to remove any potential hidden software spyware, keyloggers etc.? Or can something still persist installed in the ...
13
votes
1answer
5k views

What is the exact meaning of this gpg output regarding trust?

When I import signatures or receive a key with gpg, it outputs some cryptic lines like: gpg: 3 marginal(s) needed, 1 complete(s) needed, PGP trust model gpg: depth: 0 valid: 1 signed: 16 trust: ...
10
votes
2answers
10k views

Client-server encryption technique explanation (TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, 128 bit keys)

I opened a web page using https. When I looked at the page info provided by my browser (Firefox) I saw following: Connection encrypted: High-grade Encryption (...
217
votes
4answers
97k views

SSL3 “POODLE” Vulnerability

Canonical question regarding the recently disclosed padding oracle vulnerability in SSL v3. Other identical or significantly similar questions should be closed as a duplicate of this one. What is ...
156
votes
11answers
59k views

Why are hash functions one way? If I know the algorithm, why can't I calculate the input from it?

Why can't a password hash be reverse engineered? I've looked into this ages ago and have read lots on it, but I can't find the explanation of why it can't be done. An example will make it easier to ...

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