How to import keys from PuTTY to Ubuntu?

Question

SSH

There are private and public keys generated in PUTTYGEN and the public key is imported to the required servers.
Now how to properly import into Ubuntu to use when connecting?
At first he swore at permissions - he set 600.
Now he swears:

key_load_public: invalid format
The authenticity of host '95.X.Y.Z (95.X.Y.Z)' can't be established.
ECDSA key fingerprint is SHA256:0hekTxSGqkk32UE+zZYmeCmHVti0y9W3NSKS75jaF40.
Are you sure you want to continue connecting (yes/no)? yes 
Warning: Permanently added '95.X.Y.Z' (ECDSA) to the list of known hosts.
Load key "/home/dmitry/.ssh/id_rsa": invalid format
[email protected]'s password:

Perhaps it is necessary to recode through the same pattigen in ECDSA? or import with ssh-keygen -i -f or ssh-keyscan?

Answer 1

here it is written in detail
https://www.ylsoftware.com/news/688

Answer 2

https://www.digitalocean.com/community/tutorials/h...
Copying the public key manually