Convert between SSH key formats (OpenSSH, PEM, PuTTY) with validation. Part of the DevTools Surf developer suite. Browse more tools in the Security / Crypto collection.
Use Cases
Convert an RSA PEM key to OpenSSH format for use with a modern server configuration.
Convert a PuTTY .ppk key to OpenSSH format when switching from Windows to Linux/macOS.
Extract the public key from a private key file to add to authorized_keys on a remote server.
Convert between encrypted and unencrypted key formats for automation contexts where passphrase entry is impractical.
Tips
Convert PEM private keys to OpenSSH format for modern SSH clients — OpenSSH format (OPENSSH PRIVATE KEY) uses bcrypt-based encryption, which is more resistant to offline brute force than the legacy PEM format.
Verify the converted key by extracting the public key from both formats and comparing fingerprints — matching fingerprints confirm the conversion preserved the key.
PuTTY (.ppk) format is only needed on Windows with PuTTY clients; OpenSSH format works on Linux, macOS, and modern Windows using the built-in OpenSSH client.
Fun Facts
SSH (Secure Shell) was created by Tatu Ylönen in 1995 after a password-sniffing attack on his university network. He open-sourced the protocol specification, which led to the SSH-2 standard (RFC 4251) in 2006.
OpenSSH, the dominant SSH implementation, ships with every major Linux distribution, macOS, and Windows 10+ by default. It is maintained by the OpenBSD project and handles an estimated 80%+ of all SSH connections globally.
Ed25519 keys (introduced in OpenSSH 6.5 in 2014) are preferred over RSA-4096 for new keys: they are faster to generate, produce shorter signatures, and are resistant to side-channel attacks that affect RSA.
FAQ
Which SSH key algorithm should I use?
Ed25519 is the current best choice: fast, short signatures, and resistant to implementation errors. RSA-4096 is a safe alternative for compatibility with older SSH servers. Avoid RSA-1024 and DSA — both are deprecated.
Is it safe to convert keys in a web tool?
Only if the tool processes keys client-side without server transmission. Private key material should never leave your machine. Verify the tool's security model before pasting private keys.
