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Questions tagged [encryption]

Encryption is the process of transforming plaintext using a cipher to make it unreadable to anyone except those possessing the key.

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509 votes
8 answers

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 ...
jrdioko's user avatar
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420 votes
14 answers

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 ...
Joshua Carmody's user avatar
285 votes
3 answers

What are ssh-keygen best practices?

Most users would simply type ssh-keygen and accept what they're given by default. But what are the best practices for generating ssh keys with ssh-keygen? For example: Use -o for the OpenSSH key ...
Tom Hale's user avatar
  • 3,055
260 votes
12 answers

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 ...
Mucker's user avatar
  • 2,717
243 votes
6 answers

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 ...
ilazgo's user avatar
  • 2,773
243 votes
5 answers

What is the difference between and

Is it there any difference between the encrypted Google search (at and the ordinary HTTPS Google search (at In terms of security what were the ...
BlueBerry - Vignesh4303's user avatar
234 votes
8 answers

What is the difference between SSL vs SSH? Which is more secure?

What is the difference between SSH and SSL? Which one is more secure, if you can compare them together? Which has more potential vulnerabilities?
Am1rr3zA's user avatar
  • 3,093
209 votes
10 answers

What should you do if you catch encryption ransomware mid-operation?

You boot up your computer one day and while using it you notice that your drive is unusually busy. You check the System Monitor and notice that an unknown process is using the CPU and both reading and ...
Fiksdal's user avatar
  • 3,107
203 votes
7 answers

How do mobile carriers know video resolution over HTTPS connections?

Verizon is modifying their "unlimited" data plans. Customers in the USA can stream video at 480p -or- pay to unlock higher resolutions (both 720p and +1080p). They are not the only mobile carrier to ...
raithyn's user avatar
  • 1,843
193 votes
6 answers

ECDSA vs ECDH vs Ed25519 vs Curve25519

Among the Elliptic Curve Cryptography (ECC) algorithms available in OpenSSH (ECDH, ECDSA, Ed25519, Curve25519), which offers the best level of security, and (ideally) why?
Omar's user avatar
  • 2,033
184 votes
9 answers

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+...
Karthik's user avatar
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179 votes
8 answers

Why can't the FBI read the key embedded in the iPhone's secure chip/ROM directly from hardware (silicon)?

As far as I understand, the 4 digit passcode is combined (in some fashion) with a key stored in secure read only memory (e.g. secure enclave chip or similar), where it is directly embedded into ...
user9806's user avatar
  • 1,689
174 votes
4 answers

Where to store a server side encryption key?

I have some data that is symmetrically encrypted with a single key in my database. Rather than hard coding it into my code, I am looking for a safer way to store the encryption key. Where can I safely ...
Radek's user avatar
  • 1,843
167 votes
6 answers

Apple's open letter - they can't or won't backdoor iOS?

Apple released an open letter to the public outlining their reasons for not complying with the FBI's demands to modify the iPhone's security mechanism. Here's a summary: The FBI has an iPhone in ...
TTT's user avatar
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162 votes
6 answers

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

Isn't 128 bit security enough for most practical applications?
H M's user avatar
  • 2,987
150 votes
12 answers

Do I need to encrypt connections inside a corporate network?

Provided that I have a decent level of physical security in the office, I monitor the physical addresses of devices connected to the network and only give VPN access to trusted parties, do I need to ...
Robert Cutajar's user avatar
144 votes
14 answers

Is there any technical security reason not to buy the cheapest SSL certificate you can find?

While shopping for a basic SSL cert for my blog, I found that many of the more well-known Certificate Authorities have an entry-level certificate (with less stringent validation of the purchaser's ...
Luke Sheppard's user avatar
143 votes
9 answers

How secure is Chrome storing a password?

Whenever I enter a login into a new site, Chrome asks me if it should store the login details. I used to believe this was fairly secure. If someone found my computer unlocked, they could get past the ...
Tony Ruth's user avatar
  • 1,383
140 votes
5 answers

Is it secure to store passwords with 2 way encryption?

I'm a parent who has a parent account with my local school district so that I can log in to their website to view my child's grades etc. I clicked the "forgot password' button, and my password was ...
43Tesseracts's user avatar
  • 1,083
121 votes
4 answers

How can RFID/NFC tags not be cloned when they are passive technology?

Everywhere a question like this is asked, I see people responding that (in a scenario where a card is used) the card does some processing with the data it receives/generates some data when it receives ...
stenlan's user avatar
  • 1,271
120 votes
6 answers

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). ...
Iszi's user avatar
  • 27.1k
112 votes
9 answers

Why can we still crack snapchat photos in 12 lines of Ruby?

Just came across this bit of ruby that can be used to decrypt Snapchat photos taken out of the cache on a phone, apparently adapted from here. To my surprise, it worked without a problem, considering ...
Dmitri DB's user avatar
  • 1,181
110 votes
5 answers

What kinds of encryption are _not_ breakable via Quantum Computers?

There's the recent article NSA seeks to build quantum computer that could crack most types of encryption. Now I'm not surprised by the NSA trying anything1, but what slightly baffles me is the word "...
Tobias Kienzler's user avatar
105 votes
5 answers

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?
user310291's user avatar
  • 1,403
101 votes
3 answers

What's the advantage of using PBKDF2 vs SHA256 to generate an AES encryption key from a passphrase?

I'm looking at two comparable pieces of software which encrypt data on disk using a passphrase. One uses PBKDF2 to generate the encryption key from a passphrase, while the other uses two rounds of ...
Andrey Fedorov's user avatar
101 votes
5 answers

How can my employer be a man-in-the-middle when I connect to Gmail? [duplicate]

I'm trying to understand SSL/TLS. What follows are a description of a scenario and a few assumptions which I hope you can confirm or refute. Question How can my employer be a man-in-the-middle when ...
Lernkurve's user avatar
  • 1,144
100 votes
5 answers

What is the benefit of having FIPS hardware-level encryption on a drive when you can use Veracrypt instead?

The expensive one: The cheap one: Over 14,000 SEK difference in price. ...
Taeyang's user avatar
  • 487
97 votes
10 answers

If a provider sees the last 4 characters of my password, can they see it in full?

I have some domains/websites as well as emails with Bluehost. Every time I need support, they need the last 4 characters of my main password for the account. They cannot tell me how they store the ...
rhymsy's user avatar
  • 1,212
95 votes
15 answers

Why would someone "double encrypt"?

If I have a website or mobile app, that speaks to the server through a secured SSL/TLS connection (i.e. HTTPS), and also encrypt the messages sent and received in-between user and server on top of the ...
Lighty's user avatar
  • 2,398
93 votes
2 answers

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 ...
Jonnathan Soares's user avatar
91 votes
9 answers

Is it possible make brute-force attacks ineffective by giving false positive answers to failed log-in attempts?

I don't have any experience or scientific knowledge in security, I just wanted to ask if this is possible because I am interested in it. What if I encrypt data and every password decrypts it, but ...
Tweakimp's user avatar
  • 881
88 votes
7 answers

Why is SMS used as a way of verifying a user's mobile, when it is not even encrypted in transit?

I did some research about how secure and private SMS messages are. Providers and governments can see these SMS messages in plaintext, but what is weird is that these messages are not encrypted in ...
Mohammed Rady's user avatar
86 votes
6 answers

Why would I ever use AES-256-CBC if AES-256-GCM is more secure?

I guess the gist of my question is: Are there cases in which CBC is better than GCM? The reason I'm asking is that from reading this post by Matthew Green, and this question on cryptography stack ...
The Quantum Physicist's user avatar
84 votes
6 answers

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 ...
Vladislav Rastrusny's user avatar
80 votes
4 answers

Is it generally a bad idea to encrypt database fields?

I work on a tiny company, it's literally me (the programmer) and the owner. The owner has asked me to encrypt several fields in a database to protect the customers data. This is a web application that ...
Bhaskara's user avatar
  • 851
79 votes
3 answers

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: "", "", "", "", "". Would monitoring of packets reveal: nothing, reveal only ...
blunders's user avatar
  • 5,072
79 votes
5 answers

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?
Tyler Gillies's user avatar
78 votes
16 answers

Ensure that a file can only be decrypted after a specific date

Are there any cryptographic schemes/protocols that would allow me to encrypt a file, make it publicly available, but ensure that it can only be decrypted after specific date? I assume it would be ...
Martin Vegter's user avatar
78 votes
3 answers

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 public-...
lurscher's user avatar
  • 1,250
77 votes
10 answers

Why even use a one-time pad if the key distribution is fully secured?

I had a job interview yesterday where they asked what the only scenario where a one-time pad can be broken would be, my answer to which was "when the key distribution process is not secure enough". ...
Riley Willow's user avatar
  • 1,139
77 votes
5 answers

Advantages and disadvantages of Stream versus Block Ciphers

Encryption algorithms such as Blowfish,AES,RC4,DES and Seal are implemented in one of two categories of ciphers. What are the advantages/disadvantages to the type of ciphers?
Eric Warriner's user avatar
76 votes
12 answers

Is Google overreaching by forcing me to use TLS?

Gmail was recently changed to require HTTPS for everyone, whether they want to use it or not. While I realize that HTTPS is more secure, what if one doesn't care about security for certain accounts? ...
tylerl's user avatar
  • 83.6k
76 votes
7 answers

Why can't you work backwards with public key to decrypt a message?

As the title suggests, I am curious to know why you can't work backwards using a message, public key and encrypted message to work out how to decrypt the message! I don't understand how a message can ...
Max's user avatar
  • 879
74 votes
2 answers

How is WhatsApp sending end-to-end encrypted messages in push notifications?

WhatsApp implemented end-to-end encryption (whitepaper) in their latest update. How is it possible for WhatsApp to send push notifications with message contents to the Apple Push Notification service?...
Antwan van Houdt's user avatar
73 votes
8 answers

Are powerline ethernet adapters inherently secure?

I have 2 Zyxel PLA407 powerline adapters. Router is downstairs connected to one adapter, other adapter is upstairs about 30 feet away connected to a desktop. I have a house, not an apartment or ...
v15's user avatar
  • 1,771
71 votes
2 answers

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 ...
DaGhostman Dimitrov's user avatar
71 votes
3 answers

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, ...
Predator's user avatar
  • 961
71 votes
5 answers

What makes Random Number Generators so fragile?

It seems to me that a hardware component which generates random numbers is extremely simple - just measure tiny vibrations in the hardware with a sensor, right? Maybe I'm wrong but it seems like if ...
john doe's user avatar
  • 775
70 votes
5 answers

Understanding 2048 bit SSL and 256 bit encryption

On DigiCert's page, they advertise a 2048 bit SSL with a 256 bit encryption: What exactly is the difference here and why are two encryption bits ...
JohnJ's user avatar
  • 867
69 votes
5 answers

Is a 'dumbphone' mobile more secure for basic phone calls than a smartphone?

By dumbphone I mean: no internet connection, very limited features, etc. By more secure I mean: secure from malicious and direct hacking. I don't mean as in protected from government tapping/snooping;...
infinite-etcetera's user avatar

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