Using Existing ED25519 SSH Keys

This guide explains how to use an existing ED25519 SSH key pair (e.g., id_ed25591 and id_ed25591.pub) across different operating systems. This is useful when reusing previously generated SSH credentials on a new machine or environment.

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Key Files

• id_ed25591 — Your private key
• id_ed25591.pub — Your public key

Ensure you keep your private key secure and never share it.

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1. Ubuntu Linux

Step 1: Create .ssh Directory (if it doesn’t exist)

mkdir -p ~/.ssh
chmod 700 ~/.ssh

Step 2: Move the Key Files

Assuming the keys are in your Downloads folder:

mv ~/Downloads/id_ed25591 ~/.ssh/
mv ~/Downloads/id_ed25591.pub ~/.ssh/

Set the correct permissions:

chmod 600 ~/.ssh/id_ed25591
chmod 644 ~/.ssh/id_ed25591.pub

Step 3: Add Key to SSH Agent

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25591

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2. macOS

Step 1: Move Key Files to .ssh Folder

mkdir -p ~/.ssh
chmod 700 ~/.ssh
mv ~/Downloads/id_ed25591 ~/.ssh/
mv ~/Downloads/id_ed25591.pub ~/.ssh/
chmod 600 ~/.ssh/id_ed25591
chmod 644 ~/.ssh/id_ed25591.pub

Step 2: Add Key to SSH Agent and macOS Keychain

eval "$(ssh-agent -s)"
ssh-add --apple-use-keychain ~/.ssh/id_ed25591

Step 3: (Optional) Persist Key in SSH Config

Edit or create ~/.ssh/config:

Host *
  AddKeysToAgent yes
  UseKeychain yes
  IdentityFile ~/.ssh/id_ed25591

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3. Windows

Option A: Using Git Bash

1. Open Git Bash.
2. Move the key files to your SSH directory:

mkdir -p ~/.ssh
mv /c/Users/YourUser/Downloads/id_ed25591 ~/.ssh/
mv /c/Users/YourUser/Downloads/id_ed25591.pub ~/.ssh/
chmod 600 ~/.ssh/id_ed25591
chmod 644 ~/.ssh/id_ed25591.pub

1. Start the SSH agent and add the key:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25591

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Option B: Using Windows Subsystem for Linux (WSL)

Inside WSL (e.g., Ubuntu):

mkdir -p ~/.ssh
mv /mnt/c/Users/YourUser/Downloads/id_ed25591 ~/.ssh/
mv /mnt/c/Users/YourUser/Downloads/id_ed25591.pub ~/.ssh/
chmod 600 ~/.ssh/id_ed25591
chmod 644 ~/.ssh/id_ed25591.pub

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25591

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Verifying the SSH Key

You can test that your key is working by connecting to a server:

ssh -i ~/.ssh/id_ed25591 user@your-server.com

Or verify that the key is loaded:

ssh-add -l

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Summary

OS	Key Path	Add Command
Ubuntu	~/.ssh/id_ed25591	ssh-add ~/.ssh/id_ed25591
macOS	~/.ssh/id_ed25591	ssh-add --apple-use-keychain ~/.ssh/id_ed25591
Windows	~/.ssh/id_ed25591	ssh-add ~/.ssh/id_ed25591

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Ensure that your key is securely stored and permissions are correctly configured to avoid authentication issues.