Java

Get Public Key in Format for ~/.ssh/authorized_keys

See more SSH Key Examples

If you have an RSA private key, then by definition you also have the public key because the RSA public key is a subset of the private key. (The public key is just the modulus + exponent, whereas the private key contains additional items.)

This example converts an RSA private key to the OpenSSH format public-key (a single line of text) that can be inserted into the ~/.ssh/authorized_keys file on the SSH server to enable public-key authentication for a particular private key.

Note: On the SSH server, such as on a Ubuntu Linux computer, the sshd config file is located at /etc/ssh/sshd_config. It contains a line that indicates the authorized keys file, and the typical default is:

AuthorizedKeysFile      .ssh/authorized_keys

Chilkat2 Java

import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.SshKey;
import com.chilkatsoft.chilkat2.StringBuilder;

public class ChilkatExample {

    public static void main(String[] args) {
        // This example requires the Chilkat API to have been previously unlocked.
        // See Global Unlock Sample for sample code.

        // Load a private key from a file.  The format can be text format, such as .ppk (PuTTY private key) or .pem.
        String privateKeyPath = "/myKeys/myRsaKey.ppk";

        // Here's an example of a non-encrypted private key in ppk format:

        // PuTTY-User-Key-File-3: ssh-rsa
        // Encryption: none
        // Comment: rsa-key-20220606
        // Public-Lines: 6
        // AAAAB3NzaC1yc2EAAAADAQABAAABAQDKQUdx8EU6qIpVcT1NbL/sSnELJdifQa+K
        // kOqvgKIU30wIwGMfigSeiTFXw2jWsPcMyOIRKUvR3nf8wtR6NEj3qDfGUo3b/8Fx
        // 5BHDKuR5uU0ZJmv3Am+/hSPWOJFltL8DkxDLEpGDujLwGiUbpD9SADYhhvk9OBA7
        // 0l70hYs9gWJBjm9CR8hPg3b3F7gOYljAY2dk6W3PGmzQi+D7BTE0yYfhEOoDX7ah
        // sgrUnWIiIWK9cqLT8XbAb8gitnCmP0LerxRAkX25O4Gx/uGSrMxO/cRwz5UpiNL2
        // cciM7P4vzlbcpQiKrKaBYg5GB84QqE3xCt9cEr/qD235LpSMnWRR
        // Private-Lines: 14
        // AAABAQClKCE7PUSK3c34b3vrmX4vaapdvA3kHjNGJ4g8wAGaoazpCJDo1D9pZgZQ
        // 8FTP27ohSniwItSzD8NTN5ViJQfglBDXddo5Z+ODKQYIJSJk85etjd5j2i1+ay4U
        // ZCT2tF22gYUZDpScyJOH1RGwPLMoNtv9DMbB4uH+t46qhdJp6aWvJB7L/HUhnszc
        // qbwTG//CDL2j8Y1Mre8zvWBA8cr0I0qCzWD/Xw5MgDgpA444CFGpYb1mt8ghLniT
        // hMGgt6scUO/lnBEYo17a9N7wBexvyk0ZgEVo6nweRnCFHijNbG+C82svrsLQuL7g
        // o65BcEqLo+wBO+FtutTf2gtevZcBAAAAgQDnt2Freyfn1V93qZar06w7dXn4yV4G
        // cvQ3FmJBhk7akEFuZPOceDqrAgzS+TmsH4C96ssETdMxMO4vwEjSnZAatw6TKgnK
        // 9aDJL6/uzhk/dmBmyp7iWttN9QW9cRQvLYtwJssNDPUmF1/1cGFMpLyLfTlRBCok
        // 8dksYys4FTUfeQAAAIEA33N+LIO8i2U1NNfy2yU5GGJoFaXwPIa/CZNzZ8hbvLwm
        // 5yay4MKxGgizX+FhQ/OiEiFDEs1GDssKTXaqhE9mI/vKKLGYj9wEiWhwnawx56GI
        // WhdTZPtWkU4tYj/OkABD8vp973W1k4NEjYxVg8AoZZL1Kr4zturV8KJl9v4b/ZkA
        // AACBANAijbBLPxSTdyG9duZT89+jIdgjdjVdV5UL/xZLEh6pWbHludZHItXl62G7
        // luuJbiqhx2FANxhSu7/tAEX3z2jx7ari51Ddf/+sqfrLwc3dPkU8YXpUNYJIaNFR
        // LyzMMZvL2sPxnE6dxt4nR761y+EnTZpZ2oeSC21Lzq2xKcBp
        // Private-MAC: e0c3b5eba925944355d8d63fefcec02a982c7281a87e9994c04ce956b5c3e69b

        StringBuilder sbKey = new StringBuilder();
        try {
            sbKey.loadFile(privateKeyPath, "utf-8");
        } catch (ChilkatException e) {
            System.out.println("Failed to load the private key from a file.");
            return;
        }

        SshKey key = new SshKey();

        // If the private key file is encrypted, then you'll need to set a password.
        // If it's not encrypted, the password here is ignored.
        key.setPassword("private_key_password");

        // The FromPuttyPrivateKey method will actually auto-detect the format and correctly load any string-based format.
        // For example, you can pass in a PEM private key.
        try {
            key.fromPuttyPrivateKey(sbKey.getAsString());
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Get the public key in OpenSSH format:
        String pubKeyStr = key.toOpenSshPublicKey();
        System.out.println(pubKeyStr);

        // Sample output:
        // ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDKQUdx8EU6qIpVcT1NbL/sSnELJdifQa+KkOqvgKIU30wIwGMfigSeiTFXw2jWsPcMyOIRKUvR3nf8wtR6NEj3qDfGUo3b/8Fx5BHDKuR5uU0ZJmv3Am+/hSPWOJFltL8DkxDLEpGDujLwGiUbpD9SADYhhvk9OBA70l70hYs9gWJBjm9CR8hPg3b3F7gOYljAY2dk6W3PGmzQi+D7BTE0yYfhEOoDX7ahsgrUnWIiIWK9cqLT8XbAb8gitnCmP0LerxRAkX25O4Gx/uGSrMxO/cRwz5UpiNL2cciM7P4vzlbcpQiKrKaBYg5GB84QqE3xCt9cEr/qD235LpSMnWRR rsa-key-20220606

        // To authorize the private key for a particular SSH user account, copy the above public key into the ~/.ssh/authorized_keys file.
        // If authorized_keys already contains some keys, you can append it to a new line in the file.
    }
}