I'm very new too all this, and it took me many hours to finally get it working - thought I'd share some of the bumps I had along the way for other inexperienced folk.
Sarah's method works great (Hi Sarah - I'm a huge fan, BTW) but here's some extra tips that would have shaved hours off how long it took someone green like me:
Download openSSL here:
http://slproweb.com/products/Win32OpenSSL.html
I had to download and install Microsoft Visual C++ 2008 Redistributable Package (x64) from here: http://www.microsoft.com/en-us/download/details.aspx?id=15336 before installing openSSL.
After installing C++ THEN openssl, make sure you run ssl as an administrator (right click to get the option) to avoid issues with missing .cnf files.
I ran the commands in step 1 & 2 by running \OpenSSL-Win32\bin\openSSL.exe, and leaving off the "call openSSL" parts of Sarah's code above.
Before step 3, I had to download and install the Intermediate Certificate "Worldwide Developer Relations Certificate Authority", found on the bottom of the first page when requesting a new developer certificate.
Once I'd downloaded the cert and also made and downloaded the provisioning certificate, I copied them into \OpenSSL-Win32\bin (Not sure if this was necessary)
Then I continued to use Sarah's code in openssl (so still excluding the "call openssl" ) until step 7. I did this instead:
pkcs12 -export -inkey ios_development.key -in ios_development.pem -out iphone_dev.p12
and was then prompted to define the password I would later need to use the .p12 for generating test-builds (in my case, using Flash Pro on a Win8 machine building for an iOS7 iPad Mini)
I didn't need steps 8 through to 10 as I'm using Flash Pro, and haven't got my app to store stage yet.
I'm sure I've massively oversimplified some of this for most of you, but for novice programmers like me, this additional info would have saved a lot of wasted time.
The whole process of researching the issues I had, getting my itunes and iOS up to date, working out the problems I was having with the Apple Dev site and openSSL took me a whole day - but I've now finally got my test build running on the iOS device. And now, it's Vodka o'clock.