This one is a photo of one of the operators of the original Perplexity Contrivance, a massive cryptographic engine that was used to secure military communications during the Cuthite-Vuoshite war in the 7940s (a.k.a. the second most recent one). It completely revolutionized telecommunications, and in fact a lot of modern internet and telephony protocols ended up being based on it! Your builder friend told you about it and you've been kind of obsessed ever since.