如何在Java中将OpenSSH私钥转换为RSA私钥？

Question

I have a private key file in OpenSSH format:

-----BEGIN OPENSSH PRIVATE KEY-----
...
-----END OPENSSH PRIVATE KEY-----

but I need it in RSA format:

-----BEGIN RSA PRIVATE KEY-----
...
-----END RSA PRIVATE KEY-----

On the terminal I would do this:

ssh-keygen -p -m PEM -f my-openssh-file

but I need to do it in Java.

I've tried using org.bouncycastle.openssl.PEMWriter, but I can't work out how to convert my input key (as an input string) to a PrivateKey object that can be passed to the PEMWriter.

Answer 1

This is actually possible with the Maverick Synergy Java SSH API .

This new branch of our SSH APIs supports the new OpenSSH private key file format so you can load the new key and convert it to the old PEM format supported by BouncyCastle.

You will need the following maven dependencies:

    <dependency>
        <groupId>com.sshtools</groupId>
        <artifactId>maverick-synergy-client</artifactId>
        <version>3.0.0-SNAPSHOT</version>
    </dependency>

    <dependency>
        <groupId>com.sshtools</groupId>
        <artifactId>maverick-bc</artifactId>
        <version>3.0.0-SNAPSHOT</version>
    </dependency>

You will also need the following snapshot repository because there is no formal release of the API at the current time:

    <repository>
        <id>oss-snapshots</id>
        <snapshots>
            <enabled>true</enabled>
        </snapshots>
        <url>https://oss.sonatype.org/content/repositories/snapshots/</url>
    </repository>

First you can load the new OpenSSH private key format using:

SshKeyPair key = SshKeyUtils.getPrivateKey(
          new File("id_rsa"), "passphrase");

Then you can convert it by passing it into the older format implementation and retrieving the text via the getFormattedKey method.

System.out.write(new OpenSSHPrivateKeyFileBC(
          key, "passphrase").getFormattedKey());

As a bit of background to this answer and to declare I am the developer of the recommended project, Maverick Synergy is a third generation API that has inherited from the J2SSH Maverick and Maverick Legacy commercial APIs. Maverick Synergy is fully available as an open source product licensed under the LGPL.