Ed25519 vs RSA — which should I choose?

Ed25519 is a newer elliptic curve algorithm with shorter keys (256-bit vs RSA 4096-bit), faster signing, and stronger security. Unless the server you are connecting to does not support Ed25519 (very old OpenSSH versions), Ed25519 is strongly recommended. RSA requires at least 2048 bits; 4096 bits is recommended.

What is the difference between SSH keys and password authentication?

Password authentication requires entering a password every time you log in and is vulnerable to brute force attacks. SSH keys use asymmetric encryption: the private key stays on your local machine while the public key goes on the server. Authentication is done through cryptographic verification without transmitting passwords. Key authentication is more secure, more convenient, and ideal for automation.

How do I add my SSH public key to GitHub?

Steps: 1) Copy your public key (cat ~/.ssh/id_ed25519.pub); 2) Log into GitHub, go to Settings → SSH and GPG keys → New SSH key; 3) Paste the key and save; 4) Run ssh -T git@github.com to test the connection.

SSH connection says Permission denied — what should I do?

Troubleshooting: 1) Confirm the public key is in ~/.ssh/authorized_keys on the server; 2) Check server directory permissions: .ssh should be 700, authorized_keys should be 600; 3) Check /etc/ssh/sshd_config for PubkeyAuthentication yes; 4) Use ssh -vT for detailed error information.

SSH Keys

SSH Key Generation Guide

Ed25519 (Recommended) RSA

Open Terminal

Open Terminal application

Generate ED25519 Key Pair

Run the following command to generate a key. When prompted for the save location, press Enter to use the default path. Then set a passphrase (optional but recommended).

Terminal Command

ssh-keygen -t ed25519 -C "your_email@example.com"

💡 A passphrase adds an extra layer of protection for your private key.

Start SSH Agent

SSH Agent manages keys so you don't need to enter your passphrase every time.

Terminal Command

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

Copy Public Key

The public key needs to be added to the remote server or Git platform (e.g., GitHub).

Terminal Command

cat ~/.ssh/id_ed25519.pub

💡 Copy the entire output starting from ssh- to the email address.

Add Public Key to Remote Server

Use ssh-copy-id to add the public key to a remote server with one command.

Terminal Command

ssh-copy-id user@hostname

Verify Connection

Verify that the key configuration is working.

Terminal Command

ssh -T user@hostname

💡 For GitHub: ssh -T git@github.com

SSH Config File Template Generator

Auto-generate ~/.ssh/config configuration

Host Alias

Hostname / IP

Username

Port

Key File Path

~/.ssh/config

Host myserver
  IdentityFile ~/.ssh/id_ed25519
  IdentitiesOnly yes

Common SSH Commands Reference

Generate Key

ssh-keygen -t ed25519 -C "email"

Generate Ed25519 key pair

View Public Key

cat ~/.ssh/id_ed25519.pub

Display public key content for copying

Copy Public Key

ssh-copy-id user@host

Add public key to remote server

Start Agent

eval "$(ssh-agent -s)"

Start SSH Agent background process

Add Key

ssh-add ~/.ssh/id_ed25519

Add private key to SSH Agent

List Keys

ssh-add -l

List loaded keys

Test Connection

ssh -T git@github.com

Test GitHub SSH connection

Debug Connection

ssh -vT user@host

Verbose mode to troubleshoot connection issues

View Fingerprint

ssh-keygen -lf ~/.ssh/id_ed25519.pub

View public key fingerprint

Change Passphrase

ssh-keygen -p -f ~/.ssh/id_ed25519

Change private key passphrase

Convert Format

ssh-keygen -p -m PEM -f ~/.ssh/id_rsa

Convert key to PEM format

Remote Port Forwarding

ssh -R 8080:localhost:80 user@host

Forward remote port to local

🔒 Security Tips & Best Practices

🔑 Use Ed25519

Ed25519 is more secure and faster than RSA, with shorter keys. Choose Ed25519 unless the target system does not support it.

🛡️ Set a Passphrase

Set a passphrase for your private key. Even if the private key file is leaked, a passphrase prevents attackers from using it directly.

📁 Set Correct Permissions

Private key file permissions should be 600 (chmod 600), and the .ssh directory should be 700. Never share your private key.

🔄 Rotate Keys Regularly

It is recommended to rotate SSH keys every 1-2 years, and immediately after any suspected compromise.

🚫 Disable Password Login

After setting up SSH keys, disable password-based login on the server (PasswordAuthentication no).

📋 Use Separate Keys

Use different keys for GitHub, work servers, and personal servers for easier management and revocation.

SSH Keys

Open Terminal

Generate ED25519 Key Pair

Start SSH Agent

Copy Public Key

Add Public Key to Remote Server

Verify Connection

SSH Config File Template Generator

Common SSH Commands Reference

🔒 Security Tips & Best Practices

🔑 Use Ed25519

🛡️ Set a Passphrase

📁 Set Correct Permissions

🔄 Rotate Keys Regularly

🚫 Disable Password Login

📋 Use Separate Keys

SSH Key Generation Guide

Main Features

Use Cases

常见问题

相关工具