October 28, 2012

Shor's algorithm and Quantum Fourier Transform

This post assumes you have a sound understanding of Quantum Mechanics, more precisely eigenstates,¬†superpositions and entanglements Shor’s algorithm allows us to find a factor of any composite number $$N$$ in $$O((log\ N)^2 (\ log^k\ (log\ N)^2))$$ for any random $$k$$, which is important in this scope to understand, as cryptography’s security baseline is founded on the fact that factoring cannot happen in polynomial time - I have talked on this subject in my post Yes Diffie-Hellman is secure, quoting myself ... Read more

June 22, 2012

Patching vmware vmnet module for Linux 3.2.*

When installing vmware player 4.0.4, I had the nice surprise of finding out that the vmnet kernel module would not properly compile while starting the vmware service. 2012-06-22T15:34:41.039+01:00| vthread-3| I120: Building module vmnet. 2012-06-22T15:34:41.040+01:00| vthread-3| I120: Extracting the sources of the vmnet module. 2012-06-22T15:34:41.046+01:00| vthread-3| I120: Building module with command: /usr/bin/make -j -C /tmp/vmware-root/modules/vmnet-only auto-build SUPPORT_SMP=1 HEADER_DIR=/lib/modules/3.2.0-25-generic/build/include CC=/usr/bin/gcc GREP=/usr/bin/make IS_GCC_3=no VMCCVER=4.6 2012-06-22T15:34:41.835+01:00| vthread-3| I120: Failed to compile module vmnet! Manually directly compiling the module, we see a couple of incompatibility with the kernel header definitions ... Read more

May 4, 2012

Git :: Removing files from all commits

Alright… this is just a tiny hint on the process I used to nuke some committed files from all commit history git filter-branch --index-filter "git rm -rf --cached --ignore-unmatch my_files" HEAD rm -rf .git/refs/original/ git reflog expire --all git gc --aggressive --prune git push origin +master And here comes the explanation: git filter-branch –index-filter “git rm -rf –cached –ignore-unmatch my_files” HEAD Our action is to rewrite our branch, hence we need to use the top level “filter-branch” command. ... Read more

April 29, 2012

The so-called Skype SDK IP leaks

For the last few days, there has been a buzzing news in the community, following the recent discovery of a so-called information leak in the skype SDK. [email protected], published a python code sample “exploiting this vulnerability” https://github.com/zhovner/Skype-iplookup/ using a de-obfuscated SDK and published a demo site @http://skype-ip-finder.tk/. More related information on the skype-open-source project can be found @ http://skype-open-source.blogspot.de/ So to sump-up, the “so-called leak” takes place by: 1. having “debug logging enabled” in the hi-jacked SDK 2. ... Read more

April 22, 2012

Mercedes Museum

Here are a few snaps from my visit at the Mercedes Museum this weekend in Stuttgart - for those visiting Germany, it is definitely worth the stop. It was both cultivating and a lot of fun :) [flickr-gallery mode=“photoset” photoset=“72157629512062396”]

February 24, 2012

Lower initial TCP RTO - Redhat kernel patch

I have recently back-ported the rfc2988bis changes (initRTO=1 and fallack) to the redhat 2.6.32 kernel - find the patch on my github account at @ https://github.com/alouche/redhat-2.6.32-kernel-patches/blob/master/rfc2988bis.patch On short lived connections with a lot of 3WHS, a lower initial RTO will improve 3WHS latency by 2*2000ms*X% (X% being the average of packet drops of a specific route). For further technical details, refer to https://www.ietf.org/proceedings/77/slides/tcpm-1.pdf

February 4, 2012

Linux CFS Algorithm and Virtual Runtime

Since the 2.6.23 kernel, the Linux kernel process scheduler previously O(1) was replaced by CFS - a Completely Fair Scheduler. CFS uses a red-black tree as data-structure and unlike previous Unix process scheduler does not account a traditional time slice of process execution but accounts what is referred as the process virtual runtime, expressed in nanoseconds (as opposed to Hz or jiffies). The usage of a self-balanced tree as the red-black tree allows for a lookup of $$O(\log\ n)$$ time per the height of the tree, but more on this later. ... Read more

January 13, 2012

DCB 101 - Priority-based Flow Control

DCB - Data Center Bridging is set of standard which defines 4 set of independent technologies/concepts to pretty much make Ethernet lossless, hence to support storage traffic. We will not go into a debate over FCoE, whether you should consider a single fabric for both storage and “standard/Ethernet” traffic in your data center design strategy or go a more traditional way. As we said earlier, DCB is a set of standards, actually a set of 4 standards, which we will depict over the “DCB 101” posts series. ... Read more

October 31, 2011

Yes Diffie-Hellman is secure

When it comes to the Diffie-Hellman algorithm, there seem to be many confusions from newbies in¬†Cryptography as to whether an attacker could easily recompute the shared key by intercepting the prime numbers + public keys. While the answer is “no”, understanding why, requires an understanding the discrete logarithm problem. So here we go. ###Discrete Logarithm Problem### The discrete logarithm problem can be summarized as follow: Given $$a, b \in \mathbb{Z}/p\mathbb{Z} \wedge P$$ a prime, compute $$\log_b a$$ ... Read more

October 12, 2011

RXDSK - RapidDisk - Ram Block Device

RXDSK is a project currently in development which is worth checking out and keeping an eye on. It is quiet similar to ZRAM (previously compache) and TMPFS/RAMFS but has some minor differences which renders it more flexible for generic usage. ZXDSK allows for example an export of the ram disk to a physical disk, making it therefore usable as a swap device. According to the developer, LZO is planned to be used as a compression layer, making it therefore quiet similar in this light to ZRAM. ... Read more