Igor's Computer Blog

This post is targeted at people that understand ip addresses, default gateways and have heard of arp, but don’t play with them often enough to realize how vulnerable we are to man in the middle attacks. Back in the old days, the network hardware was often a hub, and hubs had a property that all the computers connected to a hub could see each others traffic.  This meant if my computer and tori-the-lori were on the same hub tori-the-lori could see all my network traffic. This sound like weak security.  In time the world invented switches, and now almost all networking uses switches. Switches differ from hubs in that computers only see traffic that is sent to them, not everyone's traffic.  This difference should fix the weak security right?   Well, as with most things security the devil is in the details. Lets dig in. When a computer wants to talk another computer by IP address, it needs to find the MAC address for the IP address, this is done via ARP.  Le...

Nothing annoys me more than having to argue over whitespace and indentation. Where should we stick the braces? Spaces vs Tabs? Can't we find something more useful to argue over? Long ago I read the only to end the pointless whitespace debate, is to have the compiler reject random whitespace . I thought that was a very good idea, and today I'll talk about it. In the beginning whitespace didn't matter, it was there for the human, and the program ignored it.   But that caused an annoying problem - you ended up needing tokens like '{' ';' and '(' and then you needed to argue about how you arranged the code around those tokens.  For example: ProcessIncomingDogs(List<Dog> dogs) { ... if (dogs>1) { RunAway(smallDogs,speed.Fast); Log("SmallDogs Ran Away Fast"); } Log("EveryOne Ran Away that needed to"); ... } I'm happy to say we're making progress, python gets rid of the ann...

Henry Ford takes 3 of his division presidents out for diner to decide which of them will be the new CEO. As soon as they start eating Mr. Ford chooses Bob, the man to his left, to be the new CEO. The other division presidents are shocked, and ask why Bob was picked over them. Henry replies: Bob was the only man who tasted his food before salting it. Unlike at dinner time, hashes should always be salted. A hash is a one way function that maps something, for this discussion a password, to a short string. The point of a hash is if you're given the hash, you can't figure out the password. A common scenario for hashes is checking users passwords. Instead of storing a users passowrd and checking the passwords match, you store the hash of the users password, and make sure a hash of the users password matches the hash you stored. The advantage of storing the hash is if someone steals your disk they don't get your user's passwords. There's a rub though. What happens if t...

You often use thumbprints to find certificates, but what is the thumbprint?  The thumbprint is the hash of the certificate. In the case of the CLR’s X509Certificate2 class, the thumbprint is the SHA1 hash of the certificate. If you want to compute the thumbprint of a certificate yourself it’s pretty simple: function get-CertThumbprint ($cert) { $sha = new-object System.Security.Cryptography.SHA1CNG $hashOfRawBytesOfCertificate = $sha.ComputeHash($cert.RawData) ( $hashOfRawBytesOfCertificate| % {"{0:X}" -f $_} ) -join "" } PS cert:\LocaLMachine\My> dir Directory: Microsoft.PowerShell.Security\Certificate::LocaLMachine\My Thumbprint Subject ---------- ------- 3BCA8A25A071300BD177E4C73135E54FA830039A CN=STS 08766D8B3DCDE5D633ED06AB1CB4DF4CCAECA533 CN=localhost PS cert:\LocalMachine\My> $cert = get-item 08766D8B3DCDE5D633ED06AB1CB4DF4CCAECA533 PS cert:\LocalMachine\My> $cert...

I have a day job, and in that job I use Word, OneNote and Outlook.  For style I only use bold, italics, underline, headings 1-3 and lists. For some reason, I never learned the keyboard shortcuts for some of these, and thus I need the mouse to apply these styles. In case you suffer like me, here’s are the shortcuts that will set your mouse free. Style Word OneNote Heading 1 C-A-1 C-A-1 Heading N C-A-N C-A-N Bulleted List C-S-L C-. Numbered list ? C-/ Underline C-U C-U Italics C-I C-I Bold C-B C-B Strike through ? C-- High Light ? C-H List item up A-S-Up A-S-Up List item down A-S-Down ...

Lets start with an example, as the concept of dynamic scoping is a big string for most programmers. Python Program x = 5 def printX(): print x def setAndprintX(): x=7 printX() printX() setAndPrintX() printX() Output From Python 5 5 5 Powershell Program $x = 5 function printX() { echo $x } function setAndprintX() { $x=7 printX } printX setAndprintX printX Output From Powershell 5 7 5 What is this dynamic scoping? Most programs use static, also called lexical, scoping because it's easy to understand. You figure out what is in scope by looking at the source code. In the python example, the only value of x in scope is the global value of x. By contrast, powershell uses dynamic scoping, in this model, you lookup up variables at runtime based on a scope stack. Each time you call a function you create a new scope, and copy all values from the parent scope into it. In the powershell example, when printX is called fr...