The drunken bishop

For a change, we're going to be fairly timely with this. Not with the subject of this post, but at least with the thing that sparked it. In October 2026, it came to light that the certificate authority eMudhra had been using remarkably secure private keys such as 4. That's how I came across this wonderful illustration: The key's randomart image is: +---[RSA 2048]----+ | | | | | | | | | 4 | | | | | | | | | +----[SHA256]-----+ Joking aside, the image is obviously far from reality, since these aren't actually generated from the private key, but from the public key's (SHA256) fingerprint/hash. Still, it was enough to get me wondering how they actually work. Let's look at a few real examples and see if we can get anywhere with them: +--[ED25519 256]--+ +--[ED25519 256]--+ +--[ED25519 256]--+ | | |o ..E. .o.. | |B=o+++o | | . | |.. = . ..... | |Bo+.+ +.. | | . o . | |. . = ..+.. | |*@ o o +.. | |...+ + + | |. . =+o.o | |@.o . ..o. | |.=.o+.. S o | | . ..+S.. | |= + . S. | |* * .o . | |... +…