Understanding PEM and OpenSSH Formats
Before we dive into the process of converting PEM to OpenSSH format, it is important to understand what these formats are and how they differ. PEM stands for Privacy Enhanced Mail and is a base64 encoded format used for encoding X.509 certificates, private keys, and other cryptographic data. OpenSSH is a suite of secure networking utilities used for remote login and file transfer over an encrypted network. OpenSSH uses a different format for keys, known as the OpenSSH format.
Key Differences between PEM and OpenSSH Formats
The main difference between PEM and OpenSSH formats is the way they store private keys. PEM stores private keys in a base64 encoded format, while OpenSSH stores them in a binary format. Additionally, PEM can store both the private and public key in the same file, while OpenSSH requires separate files for the private and public keys.
Converting PEM to OpenSSH Format
Converting PEM to OpenSSH format involves two main steps: extracting the private key from the PEM file and converting it to the OpenSSH format.
Extracting the Private Key from the PEM File
To extract the private key from the PEM file, we will use the OpenSSL command-line tool. The following command will extract the private key from the PEM file:
openssl rsa -in private-key.pem -outform pem > private-key.out
This command will extract the private key from the PEM file and save it in the PEM format to a new file called private-key.out.
Converting the PEM Private Key to OpenSSH Format
Once we have extracted the private key from the PEM file, we can convert it to the OpenSSH format using the ssh-keygen command-line tool. The following command will convert the private key from the PEM format to the OpenSSH format:
ssh-keygen -p -m PEM -f private-key.out
This command will prompt you to enter a new passphrase for the private key. After entering the passphrase, the private key will be converted to the OpenSSH format and saved to the same file.
FAQs – Converting PEM to Use with OpenSSH Format
What is a PEM file?
PEM (Privacy Enhanced Mail) is a base64 encoded format for secure email communication and storing digital certificates, including private keys, certificates, and public keys. PEM files are typically used in the transport of certificates and encryption keys across websites, email servers and security systems.
Why would I need to convert a PEM file to OpenSSH format?
OpenSSH requires keys be in a different format (typically OpenSSH key format). If you have a private key in PEM format that you need to use with OpenSSH, you will need to convert the key to a format that OpenSSH can use.
How do I convert a PEM file to OpenSSH format?
There are various ways to convert a PEM file to OpenSSH format, but one of the most common ways is to use the ssh-keygen command-line tool. You can use this tool to import the PEM formatted key into the keychain and then export it in the OpenSSH format.
To import the PEM formatted key using ssh-keygen, you can use the following command:
``private_key.pem
ssh-keygen -i -P passphrase -f private_key.pem > id_rsa
Whereis the path to your PEM formatted private key. Replacepassphrase` with the passphrase for the key if required.
The above command will import the key and output it in the OpenSSH format saved to the id_rsa file.
Are there any tools available to simplify the conversion process?
Yes, there are various third-party tools available that can simplify the conversion process. One popular tool is PuTTYgen which is a GUI-based utility that allows you to convert PEM keys to OpenSSH format. You can use this tool to import your PEM key and then save it in the OpenSSH format.
Will I lose any data when converting a PEM to OpenSSH format?
No, your data will not be lost when the conversion is performed correctly. The conversion process only changes the format of the key and should not cause any loss of data.
Can I use my OpenSSH-formatted key on different operating systems?
Yes, OpenSSH is supported on many different operating systems including Linux, macOS and Windows. You can use your OpenSSH formatted key on any operating system that has OpenSSH installed and configured.
Can I convert an OpenSSH-formatted key back to PEM format?
Yes, you can convert an OpenSSH key back to the PEM format using ssh-keygen. To convert the OpenSSH key to PEM, use the following command:
ssh-keygen -p -m PEM -f id_rsa
Where id_rsa is the path to your OpenSSH formatted private key.
This command will prompt you for the passphrase (if there is one) and output the key in the PEM format.