How to add public keys to KOReader authorized_keys? (Kindle)

Following this guide I have enabled KOReader's SSH on my jailbreaked Kindle, but can't access to it from FileZilla because I don't know how to add the public key to KOReader's authorized_keys.

Without keys, FileZilla returns an "Access denied. Authentication failed" message (yes, I used "root" as user, and nothing for password), so I know it's working and connectable.

I have generated a pair of SSH keys through Putty. On FileZilla, I know I have to add the private key to the "SFTP Public Key Authentication" list, but how do I add the public key to KOReader's "dropbear_ecdsa_host_key"??

The first three lines are all gibberish. I am on Windows so I can't simply >>cat so I do it manually. It doesn't matter how many times I add the public key string, it makes the SSH unable to start.

Maybe I am messing up the file format and the plugin doesn't know what to do? These are the several ways I tried adding the key string to the authorized_keys file. I really don't know how to add them correctly.

1. below

gibberish characters
gibberish characters
gibberish characters

ecdsa-sha2-nistp256
keynumbershere


2. above

ecdsa-sha2-nistp256
keynumbershere

gibberish characters
gibberish characters
gibberish characters


3. delete gibberish characters

ecdsa-sha2-nistp256
keynumbershere


I KNOW usbnet exists, but since I don't have a Linux machine to do all the SSH magic, I fear I am going to brick my Kindle's in case I tried to do it on my Windows machine.

Thanks