Turns out the CS:GO Portal message is an Easter egg, not an ARG
CS:GO went three to play and got a battle royale mode last week - but the surprises didn't end there, as players discovered a cryptic message which some speculated was an ARG to tease Portal 3. Despite the best efforts of CS:GO sleuths, however, Valve has since confirmed this is actually just an Easter egg - although it's still a pretty neat discovery.
The fun and games began when YouTube user snaileny posted a video of a "strange broadcast" they'd found on the new battle royale map dz_blacksite. According to snaileny, to hear this you have to stand in Room 3 for over two minutes before the (slightly creepy) message begins to play.
Players figured out the beginning of the list is in the NATO phonetic alphabet, and translates to PGPW50 SMS757 - the first half of which refers to the PGP word list (an extended biometric word list designed to prevent wiretapping). The transmission, when converted into the PGP word list, gives you 50 pairs of numbers and letters. Reddit user GetSomeGyros then figured out that the "SMS7" part of the message, meanwhile, refers to GSM 7-bit encoding: and when you put PGP pairings into this, you get the following message: