Granting Temporary SSH Access: Using CA Private Keys and Public Keys

Granting Temporary SSH Access Using CA Private Keys and Public Keys

This article focuses on the topic of granting temporary SSH (Secure Shell) access to users using CA (Certificate Authority) private keys and public keys. In this article, we will cover the key concepts, steps, and best practices for granting temporary SSH access to users securely and efficiently.

Why Use CA Private Keys and Public Keys for SSH Access

Using CA private keys and public keys for SSH access provides several benefits over traditional password-based authentication methods. First, private keys and public keys provide a higher level of security, as they are more difficult to guess or crack than passwords. Additionally, private keys and public keys can be easily revoked or expired, making it simple to grant temporary SSH access to users. Finally, private keys and public keys can be easily distributed and managed, reducing the administrative burden of managing SSH access.

How to Grant Temporary SSH Access Using CA Private Keys and Public Keys

The process for granting temporary SSH access using CA private keys and public keys involves several steps:

1. Create a CA private key and public key pair:
# ssh-keygen -t rsa -b 4096 -C "[email protected]"
2. Distribute the CA public key to the servers that will be granting SSH access:
# ssh-copy-id -i ca\_rsa.pub user@server1 # ssh-copy-id -i ca\_rsa.pub user@server2
3. Create a user private key and public key pair for the user that will be granted temporary SSH access:
# ssh-keygen -t rsa -b 4096 -C "[email protected]"
4. Sign the user private key using the CA private key:
# ssh-keygen -s ca\_rsa.key -I user-key-id -n user -V +5m user\_rsa
5. Distribute the signed user private key to the user:
# scp user\_rsa.pub user@client
6. Configure the server to grant SSH access to users with signed private keys:
# nano /etc/ssh/sshd\_config
Match User user
AuthorizedKeysFile /etc/ssh/authorized\_keys/%u
ForceCommand internal-sftp
PermitTunnel no
AllowAgentForwarding no
AllowTcpForwarding no
7. Restart the SSH service on the server:
# systemctl restart sshd

Best Practices for Granting Temporary SSH Access

When granting temporary SSH access using CA private keys and public keys, there are several best practices to follow:

• Use strong CA private key and public key pairs, with a minimum length of 4096 bits
• Set a short expiration time for user private key and public key pairs, such as 24 hours or 48 hours
• Revoke CA private keys and public keys when they are no longer needed
• Store CA private keys and public keys securely
• Distr
  ibute user private keys and public keys using secure methods, such as scp or ssh-copy-id
• Configure servers to allow SSH access only to users with signed private keys

References

• SSH: The Definitive Guide - Authentication
• How to Use Capabilities for SSH Authentication - DigitalOcean
• SSH Protocol - ssh.com