Need your help re country abbreviations

I was looking at a list of current Guantanamo prisoners and trying to count how many are from each country. But I am having some trouble because the USG uses some weird two-letter abbreviations for countries. For example, CH is China rather than Switzerland. I can't find a key to decipher all the country codes. Can any of you point me to a list showing the abbreviations and their corresponding countries? Thanks. Once I have that key, I can do a count and post it here.