A public SSH key is a cryptographic key used in conjunction with a private SSH key to establish secure connections between a user or process and a remote server using the SSH protocol. The public key is stored on the server, while the private key remains on the user's machine.
Understanding SSH Key Pairs
SSH keys come in pairs: a public key and a private key. They work together to authenticate a user without requiring a password.
| Key Type | Description | Storage Location | Security Importance |
|---|---|---|---|
| Public Key | Used to encrypt messages and stored on the server for authentication. | Stored in ~/.ssh/authorized_keys on the server |
Less sensitive, but still important to protect. |
| Private Key | Used to decrypt messages encrypted with the public key; must be kept secret. | Stored locally on the user's machine. | Extremely sensitive; compromising it is very risky. |
How Public SSH Keys Work
- Key Generation: The user generates an SSH key pair using a tool like
ssh-keygen. - Public Key Distribution: The user copies the public key to the remote server, typically by appending it to the
~/.ssh/authorized_keysfile in the user's home directory on the server. - Authentication: When the user attempts to connect to the server using SSH, the server uses the public key to encrypt a challenge.
- Decryption and Verification: The user's SSH client decrypts the challenge using the private key. If the decryption is successful and the challenge is answered correctly, the server authenticates the user.
- Secure Communication: After authentication, the SSH protocol uses the key pair to establish a secure, encrypted communication channel. According to the reference, the public key is used by both the user and the remote server to encrypt messages.
Security Considerations
- Protect Your Private Key: The private key is the most critical part of the SSH key pair. Never share it with anyone or store it in an insecure location.
- Key Rotation: Periodically generate new SSH key pairs and revoke older ones to minimize the risk of compromise.
- Use Strong Passphrases: Protect your private key with a strong passphrase to prevent unauthorized access if the key file is compromised.
