ed25519 fingerprint mismatch because of extra padding from AWS `=`

Question

Hello. I'm encountering an interesting scenario where the generated fingerprint for my imported/created ed25519 SSH key is different from the one reported by `ssh-keygen`.

For example:

ssh-keygen:
```
64OuseEfObM7yYiEyK7u42qN1kHj6/JGnpro1XqO4pM
```

And AWS generated the fingerprint:
```
64OuseEfObM7yYiEyK7u42qN1kHj6/JGnpro1XqO4pM=
```

So, there is extra padding for some reason. Does anyone know why that is so?

Cheers,
Gergely.

Answer

I got it.

From other posts here as well, but the answer is that they are using a base64 sha256 openssl combo like this:

```
$ cat ~/.ssh/ec2-key.pub | base64 -w0 -d | openssl dgst -binary -sha256 | base64 -w0; echo
```

Where the pub key was generated from the downloaded ec2 pem key like this:

```
ssh-keygen -y -f ~/.ssh/ec2-key.pem > ~/.ssh/ec2-key.pub
```

Answer

As per [this page](https://fileformats.fandom.com/wiki/Base64) the equal sign at the end is padding to ensure correct Base64 encoding.

ed25519 fingerprint mismatch because of extra padding from AWS `=`

Relevanter Inhalt