Conversion of SSH2 private key to openSSH format using PuTTYgen (2024)

FAQs

Conversion of SSH2 private key to openSSH format using PuTTYgen? ›

Convert the public key format from SSH2 to OpenSSH

Try to find the original SSH2 public key that was provided from the user. Otherwise, use the sshldap command to output the SSH2 public key. You may need to manually insert line-breaks at the appropriate places. Save the SSH2 public key to a file (e.g. ssh2.

Convert the public key format from SSH2 to OpenSSH

Try to find the original SSH2 public key that was provided from the user. Otherwise, use the sshldap command to output the SSH2 public key. You may need to manually insert line-breaks at the appropriate places. Save the SSH2 public key to a file (e.g. ssh2.

puttygen supports exporting your private key to an OpenSSH compatible format. You can then use OpenSSH tools to recreate the public key. Copy your private key to ~/. ssh/id_dsa (or id_rsa ).

So, the OpenSSH private key format ultimately contains a private key encrypted with a non-standard version of PBKDF2 that uses bcrypt as its core hash function. The structure that contains the key is not ASN. 1, even though it's base64 encoded and wrapped between header and footer that are similar to the PEM ones.

OpenSSH uses the SSH protocol which connects over TCP. Normally, one SSH session per TCP connection is made, but multiple sessions can be multiplexed over a single TCP connection if planned that way. The current set of Secure Shell protocols is SSH2.

SSH1 and SSH2 encrypt at different parts of the packets, and SSH1 uses server and host keys to authenticate systems where SSH2 only uses host keys. SSH2 is a complete rewrite of the protocol, and it does not use the same networking implementation that SSH1 does. Also, SSH2 is more secure.

The supported key formats are: “RFC4716” (RFC 4716/SSH2 public or private key), “PKCS8” (PKCS8 public or private key) or “PEM” (PEM public key). By default OpenSSH will write newly-generated private keys in its own format, but when converting public keys for export the default format is “RFC4716”.

With the PuTTY Key Generator you can use already existing OpenSSH keys. If the public key is already appended to the “authorized_keys” file on the remote SSH server, connect to the server with the private key. Otherwise, proceed by copying the public key to the server.

How to generate .pem file using PuTTYgen? ›

Open PuttyGen. Click File -> Load private key. Go to Conversions -> Export OpenSSH and export your private key.

Importantly, the private key for PuTTY is only available in the merged . ppk format. In the case of a passphrase-protected . ppk, we'd get a Enter passphrase to load key prompt.

Private keys can be saved in the PEM format as well, “—–BEGIN PRIVATE KEY—–“/”—–END PRIVATE KEY—–” is used to denote such files. All these headers as well the detailed PEM-encoding rules are documented in this specification. ASN. 1/DER/PEM is mostly used for TLS implementation and whenever X.

Connect to Server with Private Key

The PuTTYgen tool can be closed and PuTTY launched again. Enter the remote server Host Name or IP address under "Session". Navigate to "Connection" > "SSH" > "Auth". Click "Browse..." under "Authentication parameters" / "Private key file for authentication".

The PuTTY SSH client for Microsoft Windows does not use the same key format as the OpenSSH client. If you want to use PuTTY, you have to create a new SSH public and private key using the PuTTYgen tool or convert an existing OpenSSH private key.

ppk format isn't directly compatible with OpenSSH clients. After discussing the types and some formats for SSH keys, let's see how we can convert between them. Of course, all steps with puttygen also work in the GUI version of the tool.