Back in the analog video era, it was relatively straightforward for hackers to reconstruct what was on a screen by detecting the leakage from video cables. But...
The Memex they’re taking about (Angleton is a character from The Laundry Files) is an electromechanical filing system for microfiche.
It was never built IRL, so it’s difficult to get into the nitty-gritty of security details, but I’m pretty sure that Van Eck phreaking would get you at most the index positions of the documents being accessed, and you’d need optical surveillance to discover their content.
Same issue.
It’s not just the HDMI either, any electronic circuit produces RF interference that can theoretically be reverse-engineered by Van Eck Phreaking.
The Memex they’re taking about (Angleton is a character from The Laundry Files) is an electromechanical filing system for microfiche.
It was never built IRL, so it’s difficult to get into the nitty-gritty of security details, but I’m pretty sure that Van Eck phreaking would get you at most the index positions of the documents being accessed, and you’d need optical surveillance to discover their content.