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Hacking is Art

Hacking is Art


Secure USB boot with Debian

Tue, 06 Dec 2016 14:28:04 +0100

Foreword The moment you leave your laptop, say in a hotel room, you can no longer trust your system as it could have been modified while you were away. Think you are safe because you have a crypted disk? Well, if the boot partition is on the laptop itself, it can be manipulated and you will not notice because the boot partition can't be encrypted. The BIOS needs to access the MBR and boot loader and that loads the Linux kernel, all unencrypted. There has been some reports lately that the Linux cryptsetup is insecure because you can spawn a root shell by hitting the enter key for 70 seconds. This is not the real threat to your system, really. If someone has physical access to your hardware, he can get a root shell in less than a second by passing init=/bin/bash as parameter to the Linux kernel in the boot loader regardless if cryptsetup is used or not! The attacker can also use other ways like booting a live system from CD/USB etc. The real insecurity here is the unencrypted boot partition and not some script that gets executed from it. So how to prevent this physical access attack vector? Just keep reading this guide. This guide explains how to install Debian securely on your laptop with using an external USB boot disk, such as a standard USB memory stick. The disk inside the laptop should not contain your /boot partition since that is an easy target for manipulation. An attacker could for example change the boot scripts inside the initrd image to capture your passphrase of your crypted volume. With an USB boot partition, you can unplug the USB stick after the operating system has booted. Best practice here is to have the USB stick together with your bunch of keys. That way you will disconnect your USB stick early after the boot as finished so you can put it back into your pocket. Secure Hardware Assumptions We have to assume here that the hardware you are using to download and verify the install media is safe to use. Same applies with the hardware where you are doing the fresh Debian install. Say the hardware does not contain any malware in the form of code in EFI or other manipulation attempts that influence the behavior of the operating system we are going to install. Download Debian Install ISO Feel free to use any Debian mirror and install flavor. For this guide I am using the download mirror in Germany and the DVD install flavor. wget Verify hashsum of ISO file To know if the ISO file was downloaded without modification we have to check the hashsum of the file. The hashsum file can be found in the same directory as the ISO file on the download mirror. With hashsums if a single bit differs in the file, the resulting SHA512 sum will be completely different. Obtain the hashsum file using: wget Calculate a local hashsum from the downloaded ISO file: sha512sum debian-8.6.0-amd64-DVD-1.iso Now you need to compare the hashsum with that is in the SHA512SUMS file. Since the SHA512SUMS file contains the hashsums of all files that are in the same directory you need to find the right one first. grep can do this for you: grep debian-8.6.0-amd64-DVD-1.iso SHA512SUMS Both commands executed after each other should show following output: $ sha512sum debian-8.6.0-amd64-DVD-1.iso c3883edfc95e3b09152d46ce29a032eed1de71531549aee86bb98dab1528088a16f0b4d628aee8ac6cc420364e208d3d5e19d0dea3576f53b904c18e8f604d8c debian-8.6.0-amd64-DVD-1.iso $ grep debian-8.6.0-amd64-DVD-1.iso SHA512SUMS c3883edfc95e3b09152d46ce29a032eed1de71531549aee86bb98dab1528088a16f0b4d628aee8ac6cc420364e208d3d5e19d0dea3576f53b904c18e8f604d8c debian-8.6.0-amd64-DVD-1.iso As you can see the hashsum found in the SHA512SUMS file matches with the locally generated hashsum using the sha512sum command. At this point we are not finished yet. These 2 matching hashsums just means whatever was on the download server matches what we have received and stored locally on your disk. The ISO file and SHA512[...]

Debian 8 on Dell XPS 15

Sun, 16 Oct 2016 05:46:18 +0200

It was time for a new work laptop so I got a Dell XPS 15 9550. I wasn't planning to write a blog post of how to install Debian 8 "Jessie" on the laptop but since it wasn't just install and use, I will share what is needed to get the wifi and graphics card to work.

So first download the DVD-1 AMD64 image of Debian 8 from your favorite download mirror. The closest one for me is the Hong Kong mirror. You do not need to download the other DVDs, just the first one is sufficient. The netinstaller and CD images will not provide a good experience since they need a working network/internet connection. With the DVD image you can do a full default desktop install and most things will just work out-of-the-box.

Now you can do a regular install, no special procedure or anything will be needed. Depending on your desktop selection it will boot right into lovely GNOME3.

You will quickly notice that the wifi is not working out-of-the-box though. It is a Qualcomm Atheros QCA6174 and the Linux kernel version 3.16 shipped with Debian 8 does not support that wifi card. This card needs the ath10k_pci kernel module which is included in a newer Linux kernel package from the Debian backports archive. If you don't have the Dell docking station as neither I do, then there is no wired ethernet that you can use for getting a temporary Internet connection. So use a different computer with Internet access to download the following packages from the Debian backports archive manually and put them on a USB disk.

After that connect the USB disk to the new Dell laptop and mount the disk using the GNOME3 file browser (nautilus). It will mount the USB disk to /media/$your_username/$volume_name. Become root using sudo or su. Then install all downloaded package from USB with like this:

cd /media/$your_username/$volume_name
dpkg -i linux-base_*.deb
dpkg -i linux-image-4.7.0-0.bpo.1-amd64_*.deb
dpkg -i firmware-atheros_*.deb
dpkg -i firmware-misc-nonfree_*.deb
dpkg -i xserver-xorg-video-intel_*.deb

That's it. If dpkg finished without error message then you can reboot and your wifi and graphics card should just work! After reboot you can verify the wifi card is recognized by running "/sbin/iwconfig" and see if wlan0 shows up.

Have fun with your Dell XPS and Debian!

PS: if this does not work for you, leave a comment or write to meebey at meebey . net

Ethereum GPU Mining on Linux How-To

Sun, 07 Aug 2016 00:35:58 +0200

TL;DR Install/use Debian 8 or Ubuntu 16.04 then execute: sudo apt-get install software-properties-common sudo add-apt-repository ppa:ethereum/ethereum sudo sed 's/jessie/vivid/' -i /etc/apt/sources.list.d/ethereum-ethereum-*.list sudo apt-get update sudo apt-get install ethereum ethminer geth account new # copy long character sequence within {}, that is your # if you lose the passphrase, you lose your coins! sudo apt-get install linux-headers-amd64 build-essential wget chmod +x sudo ./ ethminer -G -F --farm-recheck 200 echo done My Attention Span is > 60 seconds Ethereum is a crypto currency similar to Bitcoin as it is based on the blockchain technology. Ethereum is not yet another Bitcoin clone though, since it has an additional feature called Smart Contracts that makes it unique and very promising. I am not going into details how Ethereum works, you can get that into great detail on the Internet. This post is about Ethereum mining. Mining is how crypto coins are created. You need to spent computing time to get coins out. At the beginning CPU mining was sufficient, but as the Ethereum network difficulty has increased you need to use GPUs as they can calculate at a much higher hashrate than a general purpose CPU can do. About 2 months ago I bought a new gaming rig, with a Nvidia GTX 1070 so I can experience virtual-reality gaming with a HTC Vive at a great framerate. As it turns out modern graphics cards are very good at hashing so I gave it a spin. Initially I did this mining setup with Windows 10, as that is the operating system on my gaming rig. If you want to do Ethereum mining using your GPU, then you really want to use Linux. On Windows the GTX 1070 produced a hashrate of 6 MH/s (megahashes per second) while the same hardware does 25 MH/s on Linux. The hashrate multiplied by 4 by using Linux instead of Windows. Sounds good? Keep reading and follow this guide. You have to pick a Linux distro to use for mining. As I am a Debian developer, all my systems run Debian, which is what I am also using for this guide. The same procedure can be done for Ubuntu as it is similar enough. For other distros you have to substitute the steps yourself. So I assume you already have Debian 8 or Ubuntu 16.04 installed on your system. Install Ethereum Software First we need the geth tool which is the main Ethereum "client". Ethereum is really a peer-to-peer network, that means each node is a server and client at the same time. A node that contains the complete blockchain history in a database is called a full node. For this guide you don't need to run a full node, as mining pools do this for you. We still need geth to create the private key of your Ethereum wallet. Somewhere we have to receive the coins we are mining Add the Ethereum APT repository using these commands: sudo apt-get install software-properties-common sudo add-apt-repository ppa:ethereum/ethereum sudo apt-get update On Debian 8 (on Ubuntu you can skip this) you need to replace the repository name with this command: sudo sed 's/jessie/vivid/' -i /etc/apt/sources.list.d/ethereum-ethereum-*.list sudo apt-get update Install ethereum, ethminer and geth: sudo apt-get install ethereum ethminer geth Create Ethereum Wallet A wallet is where coins are "stored". They are not really stored in the wallet because the wallet is just a private key that nobody has. The balance of that wallet is visible to everyone using the blockchain database. And this is what full nodes do, they contain and distribute the database to all other peers. So this this command to create your first private key for your wallet: geth account new Be aware, that this passphrase protects the private key of your wallet. Anyone who has access to that file and knows your passphrase will have full co[...]