To set up SSH access, first check for an existing key, create or select a key pair your service supports, protect the private key with a passphrase, load it into an agent if useful, and add only the public key to your account or server. Then test the connection and keep track of which key belongs to which device and purpose. The commands below are OpenSSH examples; account steps and supported algorithms depend on the service and your operating system.
Before you create a key, check what you already have
Creating another key is not always necessary. An existing pair may already be suitable, and generating a key under a filename that exists can overwrite it. GitHub recommends checking for existing keys first; see its guide to checking for SSH keys. If you do not know what an existing key is used for, do not overwrite it. Choose a new filename when generating a separate pair.
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A key pair has two parts: the private key remains on your computer, while the public key is registered with the service or server you want to access. Never upload or send the private key.
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For GitHub’s documented OpenSSH workflow, the default example uses Ed25519. The guide gives RSA with a 4096-bit key as an option for legacy systems that do not support Ed25519. These are examples for that workflow, not a guarantee that every server or client accepts both. Check your target service’s current requirements before choosing.
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Generate an Ed25519 key
- Open a terminal and run
ssh-keygen -t ed25519 -C "[email protected]", replacing the example email with an identifier you recognize. - When prompted for a file location, accept the default only if it will not overwrite a key you need. Otherwise, enter a distinct path and filename.
- Set a passphrase when prompted. Keep the resulting private key on this device.
Generate an RSA key for a legacy system
If the client or system does not support Ed25519, GitHub’s guide gives this example: ssh-keygen -t rsa -b 4096. Confirm that RSA is accepted by the service you are connecting to.
For GitHub’s full command flow and platform-specific notes, consult Generating a new SSH key and adding it to the ssh-agent.
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Protect the private key with a passphrase
A passphrase adds protection if someone gains access to the computer holding the private key. It is separate from your account password, and it does not make the key safe to share. GitHub explains the role of a passphrase in its SSH key passphrase guide.
You can change the passphrase on an existing key without creating a new pair. For the default Ed25519 path, run ssh-keygen -p -f ~/.ssh/id_ed25519. Substitute the actual private-key path if you used a different filename.
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Use ssh-agent to reduce repeated passphrase prompts
ssh-agent can hold an unlocked key for use by SSH clients, so you do not need to enter its passphrase for every operation. It does not replace a passphrase or change where the private key should be stored.
Agent startup and key loading differ by platform. GitHub’s setup guide has separate instructions for macOS Keychain integration, Windows OpenSSH service setup, and Unix-like systems. Follow the section matching your environment rather than treating one startup command as universal. On Windows, Git for Windows may use its bundled ssh.exe, which can fail to communicate with keys held by the Windows OpenSSH agent; GitHub documents configuring Git to use the system SSH binary in that situation.
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Register the public key with the service
For GitHub, the public key must be added to your GitHub account before it can authorize SSH access. The public key is typically the file with the .pub suffix; the private key has no such suffix by default. Use GitHub’s instructions for adding a new SSH key and follow the service’s current account interface. For another hosting service or server, use its own public-key registration procedure.
Test access and identify the key you are using
After registration, test the connection using the target service’s current instructions. If access fails, establish which SSH executable and agent your shell or Git client is using, then compare the local key or fingerprint with the key registered to the account. A mismatch between the SSH binary and agent can make an otherwise correctly registered key appear unavailable.
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A SHA-256 fingerprint identifies a key without revealing the private key. To list fingerprints available to the agent, run ssh-add -l -E sha256. Compare the result with the account’s key listing, and keep a record of the machine and purpose for each key.
Review, remove, or replace keys as circumstances change
Review the keys registered to your account periodically. Remove entries you do not recognize, no longer use, or no longer trust; treat a compromised key as untrusted and revoke it promptly. GitHub’s key review guidance explains how to inspect associated keys. A fingerprint helps you identify which key an entry represents without exposing its private contents.
Consider hardware-backed keys only if your setup supports them
OpenSSH supports hardware-backed key types such as ed25519-sk; GitHub also documents ecdsa-sk for hardware that does not support Ed25519. The physical security key must be connected when authenticating. Compatibility depends on the security key, OpenSSH build, operating system, and target service, so verify all of those before relying on this route.
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