Articles taggués ‘Mac OS X’

How to Protect Yourself from NSA Attacks on 1024-bit DH

03/02/2019 Comments off

nsa attacksWhen NSA gets you worrying

In a post on Wednesday, researchers Alex Halderman and Nadia Heninger presented compelling research suggesting that the NSA has developed the capability to decrypt a large number of HTTPS, SSH, and VPN connections using an attack on common implementations of the Diffie-Hellman key exchange algorithm with 1024-bit primes. Earlier in the year, they were part of a research group that published a study of the Logjam attack, which leveraged overlooked and outdated code to enforce « export-grade » (downgraded, 512-bit) parameters for Diffie-Hellman. By performing a cost analysis of the algorithm with stronger 1024-bit parameters and comparing that with what we know of the NSA « black budget » (and reading between the lines of several leaked documents about NSA interception capabilities) they concluded that it’s likely NSA has been breaking 1024-bit Diffie-Hellman for some time now.

The good news is, in the time since this research was originally published, the major browser vendors (IE, Chrome, and Firefox) have removed support for 512-bit Diffie-Hellman, addressing the biggest vulnerability. However, 1024-bit Diffie-Hellman remains supported for the forseeable future despite its vulnerability to NSA surveillance. In this post, we present some practical tips to protect yourself from the surveillance machine, whether you’re using a web browser, an SSH client, or VPN software.

Disclaimer: This is not a complete guide, and not all software is covered.

Web Browser

To make sure you’re using the strongest crypto, you have to look at the encryption algorithms (or cipher suites) that your browser supports. There’s an excellent tool, How’s My SSL?, that will test your browser’s cipher suite support. The relevant area of the page is the bottom, Given Cipher Suites. You want to make sure that you don’t see the text « _DHE_ » in the list of ciphersuites – although the Elliptic Curve variant of Diffie-Hellman, represented by suites with « _ECDHE_ » is okay. It is important to note that there is a trade-off here: removing your clients support for « _DHE_ » ciphers will eliminate the risk of this attack, but it may also remove Forward Secrecy support altogether for some sites. Here’s how to remove those « _DHE_ » cipher suites if you still have them:


(tested with 40.0.3)

Open a new tab, enter « about:config » into the location bar and hit the « Enter » key. If you get a warning page, click « I’ll be careful, I promise! » This will bring you to the Firefox configuration settings. In the search bar up top, type « .dhe_ » and hit the « Enter » key. This should result in two settings being displayed: « security.ssl3.dhe_rsa_aes_128_sha » and « security.ssl3.dhe_rsa_aes_256_sha ». Double-click both of them to change the value from « true » to « false ».


Now, if you refresh the How’s My SSL page, the « _DHE_ » ciphersuites should be gone!

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Convert HTML Page To a PDF Using Open Source Tool

08/01/2019 Comments off

Source: nixCraft

Do you need a simple open source cross-platform command line tool that converts web pages and HTML to a PDF file? Look no further, try wkhtmltopdf.

From the project home page:

Simple shell utility to convert html to pdf using the webkit rendering engine, and qt. Searching the web, I have found several command line tools that allow you to convert a HTML-document to a PDF-document, however they all seem to use their own, and rather incomplete rendering engine, resulting in poor quality. Recently QT 4.4 was released with a WebKit widget (WebKit is the engine of Apples Safari, which is a fork of the KDE KHtml), and making a good tool became very easy.

Software features

  1. Cross platform.
  2. Open source.
  3. Convert any web pages into PDF documents using webkit.
  4. You can add headers and footers.
  5. TOC generation.
  6. Batch mode conversions.
  7. Can run on Linux server with an XServer (the X11 client libs must be installed).
  8. Can be directly used by PHP or Python via bindings to libwkhtmltox.

A note about Debian / Ubuntu Linux user

You can install wkhtmltopdf using apt-get command:
$ sudo apt-get install wkhtmltopdf
$ sudo ln -s /usr/bin/wkhtmltopdf /usr/local/bin/html2pdf

Sample outputs:

[sudo] password for vivek:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 10 not upgraded.
Need to get 116 kB of archives.
After this operation, 303 kB of additional disk space will be used.
Get:1 squeeze/main wkhtmltopdf amd64 0.9.9-1 [116 kB]
Fetched 116 kB in 2s (49.4 kB/s)
Selecting previously deselected package wkhtmltopdf.
(Reading database ... 274164 files and directories currently installed.)
Unpacking wkhtmltopdf (from .../wkhtmltopdf_0.9.9-1_amd64.deb) ...
Processing triggers for man-db ...
Setting up wkhtmltopdf (0.9.9-1) ...

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Categories: Logiciel Tags:

How to Prevent & Disable Mac OS X From Sleeping From the Command Line Terminal Application

01/01/2019 Comments off

Source: nixCraft

I’m running a process to complete backup and covert images in Mac OS X laptop. I do not wish to disable sleep manually from my OS X power options (Energy Saver). How do I temporarily prevent a Mac from sleeping while my process is still active in Mac OS X Unix operating systems? How can I prevent the system from sleeping temporarily from the command prompt?

You can use the caffeinate command. This command creates assertions to alter system sleep behavior. If no assertion flags are specified, caffeinate creates an assertion to prevent idle sleep.

Another option is to use the pmset command to manipulate power management settings.



The syntax is:

caffeinate [options]
caffeinate [options] command

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Categories: Système Tags: , ,

A Shell Primer: Master Your Linux, OS X, Unix Shell Environment

29/12/2018 Comments off

On a Linux or Unix-like systems each user and process runs in a specific environment. An environment includes variables, settings, aliases, functions and more. Following is a very brief introduction to some useful shell environment commands, including examples of how to use each command and setup your own environment to increase productivity in the command prompt.


Finding out your current shell

Type any one of the following command at the Terminal app:

ps $$
ps -p $$


echo "$0"

Sample outputs:

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Categories: Système Tags: , ,

Set a Custom New Tab Page in Firefox

16/12/2018 Comments off



Firefox: If you’re not a big fan of the new speed dial tab in the newest version of Firefox, Mozilla blog Mozilla Links shows how you can customize the page to load any site of your choosing with a simple edit to the about:config file.

Categories: Logiciel Tags: , , ,