Category: security

computer security related topic

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How to Setup SSH public-key or password-less authentication in Ubuntu

Here’s how to setup public-key (or passwordless) authentication in Ubuntu or any other Linux based operating system that use OpenSSH.

First make sure you’ve remote SSH server running and accepting connection. Then you need to generate ssh key on local server (I prefer RSA). You can enter passphrase for added security, or leave it blank for passwordless authentication.

local:~$ ssh-keygen -t rsa
Enter passphrase (empty for no passphrase):

The command will generate id_rsa and id_rsa.pub files. The files will be save in ~/.ssh/ directory. Then copy id_rsa.pub file to the remote server using SCP. Read How to use SCP on Linux or other UNIX-based Environment for more information about SCP

local:~$ scp id_rsa.pub username@remote.host:~/

Then you have to connect to the remote host and append the id_rsa.pub public key file to the list of “authorized_keys“. Don’t forget to chmod the authorized_keys file and .ssh directory, or OpenSSH won’t work correctly

local:~$ ssh username@remote.host

#now we are on remote server!
remote:~$ cat id_rsa.pub >> ~/.ssh/authorized_keys
remote:~$ chmod 644 ~/.ssh/authorized_keys
remote:~$ chmod 700 ~/.ssh

Make sure you have edited the “/etc/ssh/sshd_config” file to allow Public key authentication and RSA authentication.

#sshd_config file

PermitRootLogin no
...snip...
RSAAuthentication yes
PubkeyAuthentication yes
...snip..

Save and restart sshd server daemon by running the following command.

remote:~$ sudo /etc/init.d/ssh restart

After that, logout from the remote host to test the Public-key authentication


remote:~$ exit
local:~$

Testing the SSH public-key authentication
To test the public-key authentication, simply connect to remote server normally using ssh, and if things have gone smoothly you’ll be prompted to enter your passphrase, instead of password.


local:~$ ssh username@remote.host
Enter passphrase for key '/home/username/.ssh/id_rsa':

Note that you will not be prompted to enter passphrase/password if you’ve generated a key with “blank passphrase“, effectively making your login “passwordless”. For added security, it is advised that you disable normal interactive-keyboard password option and rely fully on public-key authentication by changing sshd_config line from:

PasswordAuthentication yes

to


PasswordAuthentication no

p/s: this tutorial was adapted from Shortest passwordless ssh tutorial, ever with updated notes for latest OpenSSH release

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How to setup Secure Webserver HTTPS (SSL) on Apache in Ubuntu

Secure HTTP (SSL/TLS) has become a must if you are planning to setup a website which includes user authentication (ie. login box) or sensitive data. HTTPS prevents the sensitive data from being transfered across the network in clear text where it is susceptible to being sniffed or altered. Here is the tutorial on how to setup a secure HTTP on Apache web server in Ubuntu 10.04 (Lucid Lynx).

What do you need?

  • apache2 (Web Server)
  • openssl
  • A bit patient, because it will take some time to learn

Step 1: Create a self-signed certificate
You need to create a self-signed certificate with openssl. To do that you will need to generate the server key.


openssl genrsa -des3 -out server-sec.key 4096

…and certificate signing request (CSR)


openssl req -new -key server-sec.key -out server.csr

After that, generate the server certificate by signing it with the server key.

openssl x509 -req -days 365 -in server.csr -signkey server-sec.key -out server.crt

Keep the server-sec.key in a secure location, with read/write permission assigned only to root. Then generate a password-less copy of the key for Apache use.

openssl rsa -in server-sec.key -out server.key

By this time, you should have :

  • server.key (passwordless key for Apache)
  • server.csr (certificate signing request)
  • server.crt (certificate)
  • server-sec.key (server key)

Continue reading “How to setup Secure Webserver HTTPS (SSL) on Apache in Ubuntu”

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How to use GNU Privacy Guard (GPG) – Encrypt, Decrypt, Sign and Verifying identities

GPG or the GNU Privacy Guard is a free and open source software that implements OpenPGP public-key cryptography message format (RFC4880). You can use GPG to encrypt, decrypt, sign and verify files or emails. To use GPG, you need to generate the public-key/private-key pairs in your computer by running this command, and choose the default option


gpg --gen-key

The application will ask you to enter your ID and passphrase, make sure you choose a strong passphrase to guarantee the safety and security of your keys.

Encrypting and Decrypting Files
You can use GPG to encrypt files, it can be only decrypted by those who have your public-key. The command that can be used to encrypt file is :

gpg --out encrypted_file.txt --encrypt original_file.txt

Run this command to decrypt. Files encrypted with private key can only be decrypted with public key and vice-versa.

gpg --out decrypted.txt --decrypt encrypted_file.txt

Signing Email or body of texts
Alternatively, you can chose to sign emails/texts instead of encrypting them. Signing files is a way to ensure that the message/texts/emails are from the right sender and its content has not been tempered with. You can run this command to sign email or texts :

gpg --clearsign original_text.txt

This will produce a signature file which content the original text with PGP signature embedded at the bottom of the message.

To verify it (assuming you have the public key), you need to run this command:

gpg --verify original_text.txt.asc

Continue reading “How to use GNU Privacy Guard (GPG) – Encrypt, Decrypt, Sign and Verifying identities”

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How to block ads and malware websites using /etc/hosts files in Ubuntu

Here’s an easy way to block annoying advertisement and malware sites using ‘/etc/hosts’ file.

First edit the /etc/hosts files using your favorite text editor :

sudo gedit /etc/hosts

Then, paste the list of ads/malware servers in the ‘hosts’ file. You can get the list from http://someonewhocares.org/hosts/ or by searching through Google.

Close the file, and Save. The change will take effect immediately after that. One of the side-effect from this modfication is that your web surfing experience would be significantly faster because your browser does not have to wait for the annoying advertisement to load.

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Google Malware Warning Fucked up?

I don’t know when this thing happened exactly, but I noticed it around 10:57 pm MYT (GMT+8) when I was searching information for Yaesu VX8R handheld radio.

It seems somehow the Google Malware Warning fucked up and labels all the search result as “may harm your computer”. Funny thing is, Google labels its own website as potentially spreading malware.

Google Calendar site is spreading malware?
Google Terfakap

This incident has showed me how reliant to Google i’ve become, which made me wonder what would happen if suddenly somebody might take advantage of our dependency to Google, and do nasty things to us and to our data? By the way, Google already know what you do, who you are, and where you live.

Update: This event has been slashdotted, MAKE Magazine blog also covered the story.

Update 2: Google somehow have fixed the issue at 11:22 pm MYT (GMT +8). Let’s see what they would say about this strange phenomenon.

Update 3: Thanks to Manley, it seems Google has not fixed the issue, but rather disabled the Malware warning on its search result.

Final Update : Google issued a statement in their official blog as well as StopBadware.org