Several ed25519 keys with the same prefix

Question

I have created a bunch of ed25519 keys through ssh-keygen to connect to different machines I have access to. However, I noticed that all of them begin with the same, rather long prefix:

AAAAC3NzaC1lZDI1NTE5A...

why is that? Is it a security issue? A bug? Or just some property of all ed25519 keys I don't know?

The same question was previously asked here: https://unix.stackexchange.com/q/414448/68601 — kasperd, Sep 21 '18 at 10:02
Didn't find it... was looking for "common prefix" and alike.... — CygnusX1, Sep 21 '18 at 14:10

score 6 · Accepted Answer · answered Sep 21 '18 at 09:30

This is perfectly normal. The SSH key type is encoded in BASE64 encoding at the beginning of the public key and is necessarily always the same for the same key type.

echo 'AAAAC3NzaC1lZDI1NTE5AAAA' | base64 -d

ssh-ed25519

See this for more details.

Several ed25519 keys with the same prefix

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