How to Use the Command 'keychain' (with examples)

Keychain is a powerful utility designed to simplify the management of SSH and GPG keys by allowing users to re-use ssh-agent and/or gpg-agent across different logins and sessions. This helps avoid repeated manual passphrase inputs for SSH and GPG key usage, providing a seamless and secure workflow for users. The command streamlines the authentication processes, significantly benefiting developers and system administrators who frequently work on remote servers or utilize cryptographic signing.

Use Case 1: Check for a Running ssh-agent, and Start One if Needed

Code:

keychain

Motivation:
When working with SSH keys, it’s crucial to have an SSH agent running to manage key authentication without repeatedly entering passphrases for secure shell connections. By using the keychain command, you can ensure that an SSH agent is running, and if it is not, the command will initiate one for you. This eliminates the manual setup process, enhances productivity, and ensures that your secure connections are always seamless.

Explanation:
The command keychain checks if an SSH agent is already running. If not, it starts an instance of ssh-agent. This means you don’t have to manually start an agent at each login or create scripts to do it for you. The keychain serves as a persistent store across logins, providing ease of access to the users.

Example Output:

* keychain 2.8.5 ~ http://www.funtoo.org
* Found existing ssh-agent: 2021
* Known ssh key: /home/user/.ssh/id_rsa

Use Case 2: Also Check for gpg-agent

Code:

keychain --agents "gpg,ssh"

Motivation:
Many users utilize both SSH and GPG keys for different purposes, such as code signing and secure communication. By leveraging this command, you can ensure that both ssh-agent and gpg-agent are running as needed, minimizing the hassle of manually handling multiple agents. This use case is particularly useful for developers who need both functionalities seamlessly integrated into their workflow.

Explanation:
The --agents option specifies which agents should be started or checked. By providing "gpg,ssh", the command instructs keychain to verify and potentially start both the gpg-agent and the ssh-agent, ensuring that all your cryptographic needs are met with a single command.

Example Output:

* keychain 2.8.5 ~ http://www.funtoo.org
* Found existing ssh-agent: 2045
* Known ssh key: /home/user/.ssh/id_rsa
* Starting new gpg-agent
* Known gpg key: XXXXXXX

Use Case 3: List Signatures of All Active Keys

Code:

keychain --list

Motivation:
Listing the signatures of all active keys is critical for users who maintain multiple keys and require verification of which keys are currently active. This command provides a clear and immediate overview, allowing users to maintain control and oversight over their security credentials, particularly in environments with stringent security policies.

Explanation:
The --list option directs keychain to output the signatures for the active keys managed by the agents. It allows users to quickly review which keys are loaded, giving them an opportunity to unload any that may not be needed or verify that required keys are active.

Example Output:

The following identities are available:
1. /home/user/.ssh/id_rsa
2. /home/user/.ssh/id_dsa

Use Case 4: List Fingerprints of All Active Keys

Code:

keychain --list-fp

Motivation:
In scenarios where security is paramount, such as verifying fingerprints before adding a new public key to a server’s authorized keys list, listing the fingerprints of active keys is indispensable. This command serves as a security check to ensure that you are working with the correct keys without relying solely on filenames or other less secure identifiers.

Explanation:
With --list-fp, keychain provides the cryptographic fingerprints of the active keys. This feature is particularly valuable for users needing to verify identities or perform cryptographic tasks where the fingerprint is used as the identifier for the key rather than its filename.

Example Output:

The following fingerprints are available:
1. SHA256:L8H5... /home/user/.ssh/id_rsa
2. SHA256:0p2Q... /home/user/.ssh/id_dsa

Use Case 5: Add a Timeout for Identities Added to the Agent, in Minutes

Code:

keychain --timeout 60

Motivation:
Setting a timeout for identities is essential for users concerned with security. By automatically unloading keys after a set period, users reduce the risk of unauthorized access in case of a forgotten session. This feature enhances security by limiting the keys’ availability to a predefined window, thereby protecting sensitive operations.

Explanation:
The --timeout option allows users to specify a duration for which the keys should remain active within the agent. In this example, 60 signifies that the identities will be removed from the agent after 60 minutes of inactivity, thereby offering a balance between security and convenience.

Example Output:

Identities will expire from the agent after 60 minutes of inactivity

Conclusion:

Keychain simplifies the management of SSH and GPG keys, ensuring that users can efficiently handle secure connections and cryptographic tasks across multiple sessions with minimal manual intervention. By exploring different use cases, as illustrated above, users can tailor keychain functionalities to optimize their workflow, enhancing both productivity and security.