What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
To generate an SSH key with PuTTY, open PuTTYgen, choose an SSH-2 key type accepted by your server, set its strength where offered, click Generate, then save the private key as a protected .ppk file. Copy the complete one-line key from Public key for pasting into OpenSSH authorized_keys file into the target account’s ~/.ssh/authorized_keys file. Finally, load the matching .ppk in PuTTY under Connection > SSH > Auth and connect with that account’s username.
Antihost offers Linux VPS plans with full root access, unlimited traffic on a 1 Gbps port and a 14-day free trial.
What you are creating
SSH public-key authentication uses a pair of mathematically related keys. The private key stays with the client computer and proves that you possess the credential. The public key is installed on the server account that you want to access. During login, the server checks the public key while PuTTY demonstrates possession of the corresponding private key; the private-key contents are not pasted into the server account.
As an Amazon Associate I earn from qualifying purchases.
Outdated Drivers Are Slowing You Down
One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchPC Slower Than It Used to Be?
A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11PuTTY normally stores its private key in its own PuTTY Private Key format, identified by the .ppk extension. OpenSSH servers generally expect the public half as one OpenSSH authorized_keys line. These are separate concerns: a PuTTY client can keep using a .ppk private key while the server receives the OpenSSH-formatted public-key text copied from PuTTYgen.
Before opening PuTTYgen
- Install the PuTTY suite or have the
puttygenutility available. - Know which SSH-2 algorithm your server and organizational policy permit. PuTTY documentation lists RSA, DSA, ECDSA, and EdDSA for SSH-2.
- Have an existing way to log in to the server so you can add the public key to the account. Key generation does not install anything remotely by itself.
- Know the exact username whose account should receive the key. A valid key placed in another account’s file will not authenticate the account you use in PuTTY.
- Choose a protected local location for the private key. Anyone who obtains an unprotected private key may be able to authenticate wherever its public key is trusted.
SSH-1 is obsolete and is rarely needed. For an ordinary modern connection, select an SSH-2 type accepted by the server instead of SSH-1.
#1 Best Overall
Generate the key pair in PuTTYgen
1. Start PuTTYgen
Open PuTTYgen from the installed PuTTY suite, or launch the standalone puttygen utility. The main window contains controls for the key type, key strength, generation area, comment, passphrase, and save buttons.
2. Select an SSH-2 key type
Under the key-type controls, choose the algorithm that the server accepts. The available SSH-2 families documented for PuTTY are RSA, DSA, ECDSA, and EdDSA. The strongest choice is not simply the newest-looking name: it must also be accepted by the server’s SSH policy and by every client or library that will use the key. If a server administrator has specified one type, follow that requirement. Do not select SSH-1 for a normal current deployment.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errors3. Set the requested key size
Some algorithms expose a key-size field and others may present different controls. Set the strength requested by the server administrator or organizational policy. PuTTY’s documentation describes this stage as selecting both the type of key and its strength. If the selected algorithm does not expose a size option, continue with the controls PuTTY provides rather than trying to apply an unrelated size value.
4. Click Generate and provide randomness
Click Generate. In the Windows graphical interface, PuTTYgen asks you to move the pointer over the blank area of the window. Keep moving it as requested while the utility gathers randomness and constructs the pair. The key display and the remaining controls become available when generation finishes.
Rank #2
- Used Book in Good Condition
5. Add a comment you can recognize
Enter an identifying comment in the comment field. A useful comment distinguishes this key from others when you administer several servers, computers, or accounts. The comment is metadata attached to the public-key text; it does not replace the algorithm prefix and it does not act as a password.
6. Protect the private key with a passphrase
Enter a passphrase before saving. The passphrase encrypts or protects the private-key file so that copying the file alone is not equivalent to knowing the credential. Record the passphrase through your normal secure process: PuTTY cannot use an encrypted .ppk without it, so forgetting it prevents the saved file from being used.
Recommended Free Tools
7. Save the PuTTY private key
Click Save private key, confirm any warning about saving without a passphrase only if you intentionally accept that risk, and store the resulting file in a protected location. PuTTY’s manual explicitly identifies this button as the step that writes the private key to disk. Keep the original .ppk when PuTTY remains part of your workflow; it is the file PuTTY will load later.
Copy the correct public key to the server
Use the OpenSSH authorized_keys field
PuTTYgen displays a box labeled Public key for pasting into OpenSSH authorized_keys file. Select and copy the entire key from that box. Include the algorithm prefix at the beginning and the trailing comment, if one is present. Do not copy only the visible middle portion, and do not substitute a different public-key export merely because it looks similar.
Install it for the intended account
Use an existing login method to reach the server and append the copied line to the target account’s ~/.ssh/authorized_keys file. The account represented by that path must match the username you will enter in PuTTY. Preserve the key as one uninterrupted line: the algorithm, encoded key data, and optional comment belong together. A wrapped, truncated, or accidentally split line is not the same credential.
OpenSSH authorized_keys syntax is different from the RFC 4716 public-key export format. When the server expects authorized_keys, use the single-line text from PuTTYgen’s specifically labeled OpenSSH box. Do not paste a multi-line RFC 4716 export into that file.
Configure PuTTY to authenticate with the key
- Open PuTTY and create or edit the session for the server.
- Enter the server address and connection details required by your environment.
- Navigate to Connection > SSH > Auth. The exact wording or placement can vary slightly between PuTTY releases.
- Use the private-key file control to browse to the saved
.ppkfile. - Return to the session’s connection settings if needed and enter the same username whose
~/.ssh/authorized_keysfile contains the copied public key. - Connect. When PuTTY prompts for the key’s passphrase, enter the passphrase used when the
.ppkwas saved.
The server authenticates against the installed public key; PuTTY proves possession of the corresponding private key. If the pair, username, file path, or algorithm does not match, authentication fails even though the key file itself opens normally.
Choose among RSA, DSA, ECDSA, and EdDSA
PuTTY documentation lists these as SSH-2 choices, but the practical decision is governed by the receiving server and your organization’s policy. Check the server’s accepted algorithms before generating a key, especially when a hosted service or an older SSH implementation is involved.
| SSH-2 type | What to verify before choosing | When it is appropriate |
|---|---|---|
| RSA | Whether the server’s SSH policy and your client/library support the requested RSA strength. | Use when the server or organizational policy specifically accepts or requires RSA. |
| DSA | Whether the server still permits DSA and whether policy allows it. | Only for an environment that explicitly accepts this legacy-compatible choice. |
| ECDSA | Whether the server, client, and libraries support the selected ECDSA configuration. | Use when your server policy and toolchain name ECDSA as an accepted SSH-2 option. |
| EdDSA | Whether every participating server and client/library supports the EdDSA variant PuTTYgen offers. | Use when the server and policy support it and interoperability has been confirmed. |
There is no useful “best” algorithm independent of the server. A key rejected by policy cannot be made valid by changing its comment or saving it again; generate a new pair using an accepted SSH-2 type instead.
Understand private-key and public-key formats
The .ppk private-key file
The .ppk file is PuTTY’s native private-key format. Keep it when PuTTY is the client that will make the connection. Saving the private key and copying the public key are separate operations: the server never needs the private .ppk file for ordinary public-key authentication.
The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →OpenSSH public-key text
The public-key line copied from PuTTYgen is intended for an OpenSSH authorized_keys file. It contains the algorithm identifier, the encoded public key, and, if supplied, the comment. Keep that complete sequence on one line when adding it to the account file.
Converting for another client
PuTTYgen can save a public key separately, and its manual notes that the public key can later be recovered by loading the private key again. If another program requires an OpenSSH private-key format, use PuTTYgen’s SSH-2 private-key conversion options, or configure that program to accept .ppk when it supports PuTTY’s format. Preserve the original .ppk if PuTTY will still be used; conversion should add an interoperability copy rather than silently replacing the working file.
| Consumer | Private-key file to provide | Public-key text to install on an OpenSSH server |
|---|---|---|
| PuTTY | PuTTY .ppk |
Single-line text from PuTTYgen’s OpenSSH authorized_keys box |
| A client that requires OpenSSH private-key format | Converted SSH-2 private key in the format that client specifies | The same server-compatible OpenSSH authorized_keys line |
Troubleshoot a failed connection
“Server refused our key”
- Confirm that you copied the line from Public key for pasting into OpenSSH authorized_keys file, not from a different public export.
- Check that the line in
~/.ssh/authorized_keysis complete, remains on one line, and was not wrapped or truncated during copying. - Verify the server path and the username. The public key must be in the account whose name PuTTY sends during login.
- Make sure PuTTY is loading the matching private key, not another
.ppkgenerated for a different account or server.
A passphrase prompt appears
A passphrase prompt is expected when the saved .ppk is encrypted. Enter the passphrase used at save time. This prompt is local key protection; it is not the server asking for a different public-key value.
The server rejects the algorithm
Generate another SSH-2 key using a type accepted by the server’s current SSH policy. SSH-1 is obsolete and should not be selected for ordinary modern connections. Changing the key size or comment cannot overcome an algorithm policy rejection.
Another client reports a format error
The receiving program may not consume PuTTY’s .ppk format. Convert the private key with PuTTYgen’s SSH-2 conversion options, or configure the client to accept .ppk if that option exists. Do not convert the public-key line into an unrelated export format when the server expects OpenSSH authorized_keys syntax.
The public-key file was lost
You do not have to generate a replacement pair merely because the separate public-key text was deleted. Reload the private .ppk in PuTTYgen and copy the public-key text again from the OpenSSH authorized_keys box. A newly generated pair would require installing a new public key on every server that should trust it.
Verification checklist before you close the session
- The selected key type is SSH-2 and is accepted by the server.
- The requested key strength was set where the algorithm exposed that control.
- The private key was saved as a
.ppkfile in a protected location. - A passphrase was set and can be supplied when PuTTY asks for it.
- The complete one-line public key came from PuTTYgen’s OpenSSH authorized_keys field.
- The line was added to the intended account’s
~/.ssh/authorized_keyswithout wrapping or truncation. - PuTTY’s Connection > SSH > Auth setting points to the matching
.ppk. - The username used by PuTTY is the account that owns the installed public key.
Key facts to remember
Generate once in PuTTYgen, protect and retain the private .ppk, and install only the matching public-key line on the server. The public key can be recovered from the private file, but the private file should not be copied into authorized_keys. When a connection fails, check the source field, one-line formatting, account path, username, selected algorithm, and loaded private key in that order.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
Free tools Windows power users keep installed
One-click scans. No signup required.
