58 lines
2.7 KiB
Markdown
58 lines
2.7 KiB
Markdown
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#documentation
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## Terms
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The following terms should be standardized across the document.
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#### Client
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- The user side local computer that connects *to* a remote host, typically a server.
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- This side has the **private key**, which you should keep secure
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- The private key decrypts data
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#### Server
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- The remote computer that the client connects to.
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- This side has the **public key**, which doesn't need to be secure
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- The public key encrypts data
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## SSH Keypairs
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SSH keypair authentication relies on asymmetrical encryption, and is only used for authentication. Once they exchange the needed info, they use the Diffie-Hellman Key Exchange Algorithm to create a symmetrical key(can decrypt and encrypt). This is used to encrypt the rest of the session.
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## Setup
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1. Generate an SSH keypair from the *client* with:
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```
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ssh-keygen -t ed25519
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```
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- Note: while ed25519 encryption is much more secure than rsa4096, it's not universally supported. When using older versions of OpenSSH, generate a key with `ssh-keygen -t rsa -b 4096` to generate an rsa4096 keypair. This should be compatible with almost every implementation of SSH.
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2. Follow the prompts onscreen:
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- You will be asked where to save the key, the default location is typically correct(`~/.ssh/KEYNAME`) where `KEYNAME` is the name of your keypair.
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- You will then be prompted for a password. This password is used alongside the keypair, and is optional(leave blank if you want passwordless login)
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3. Copying the public key to the server
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- There should now be two files in `~/.ssh` with the format `id_ENCRYPTIONMETHOD` and `id_ENCRYPTIONMETHOD.pub` (EG: `id_ed25519` and `id_ed25519.pub`)
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```
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ssh-copy-id USERNAME@SERVERADDRESS
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```
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- EG: `ssh-copy-id foo@192.168.0.10`
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- Restart the SSH daemon, and test for functionality
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## Further Configuration
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### Disabling password based login
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1. Edit `/etc/ssh/sshd_config` to have an uncommented line that says:
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```
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PasswordAuthenntication no
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```
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- This will prevent clients from logging on with a password entirely, unless the SSH key was configured with a passcode.
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- Reload the SSH daemon.
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### Storing keys on github
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1. See https://docs.github.com/en/authentication/connecting-to-github-with-ssh/adding-a-new-ssh-key-to-your-github-account about adding keys, access public keys at `https://github.com/USERNAME.keys`
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- You can then add public keys to your server with `curl https://github.com/USERNAME.keys | tee -a ~/.ssh/authorized_keys`
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- A similar method should exist across most git clients.
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---
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## Further Reading
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- https://www.hostinger.com/tutorials/ssh
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- https://www.hostinger.com/tutorials/ssh-tutorial-how-does-ssh-work
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- https://www.digitalocean.com/community/tutorials/ssh-essentials-working-with-ssh-servers-clients-and-keys
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