How to Convert File Encodings (DER, JKS, PEM) for TLS/SSL Certificates and Keys

Client and server processes require specific file formats for certificates, keys, and other digital artifacts used for TLS/SSL encryption. For example, when TLS is enabled, Cloudera Manager Server presents Java KeyStore (JKS) formatted key and certificate to requesting Cloudera Manager Agent hosts. The Hue client also connects to Cloudera Manager Server, but Hue requires a PEM-formatted key and certificate, rather than JKS. The PEM format used by Cloudera Manager is PKCS #8, which handles certificates and keys as individual Base64-encoded text files.

If you receive binary DER files from your certificate authority, you must convert them to the appropriate format. Since neither Java Keytool nor OpenSSL work directly with PKCS format, many of the configuration tasks detailed in How to Configure TLS Encryption for Cloudera Manager involve converting formats, or extracting keys or certificates from an artifact in one format to another.

Certificates issued by a CA in one format (encoding) can be used to create certificates in a different format using Java Keytool and OpenSSL as detailed below.

Converting DER Encoded Certificates to PEM🔗

OpenSSL can be used to convert a DER-encoded certificate to an ASCII (Base64) encoded certificate. Typically, DER-encoded certificates may have file extension of .DER, .CRT, or .CER, but regardless of the extension, a DER encoded certificate is not readable as plain text (unlike PEM encoded certificate).

A PEM-encoded certificate may also have file extension of .CRT or .CER, in which case, you can simply copy the file to a new name using the .PEM extension:

cp hostname.cer hostname.pem

To convert a DER-encoded certificate to PEM encoding using OpenSSL:

openssl x509 -inform der -in hostname.cer -out hostname.pem

For example:

openssl x509 -inform der -in /opt/cloudera/security/pki/hostname.cer -out /tmp/hostname.pem

Converting JKS Key and Certificate to PEM🔗

This process uses both Java keytool and OpenSSL (keytool and openssl, respectively, in the commands below) to export the composite private key and certificate from a Java keystore and then extract each element into its own file.

The PKCS12 file created below is an interim file used to obtain the individual key and certificate files.

Replace hostname-keystore, cmhost, hostname, and password with values from your system.

Export the private key and certificate command line:

$ keytool -importkeystore -srckeystore /opt/cloudera/security/jks/hostname-keystore.jks \
-srcstorepass password -srckeypass password -destkeystore /tmp/hostname-keystore.p12 \
-deststoretype PKCS12 -srcalias hostname -deststorepass password -destkeypass password

Extract the certificate file from the resulting PKCS12 file:
```
$ openssl pkcs12 -in /tmp/hostname-keystore.p12 -passin pass:password  -nokeys \
-out /opt/cloudera/security/pki/hostname.pem
            
```
This extracted certificate can be used, as is, but you can additionally extract the private key from the keystore as detailed in the next section.

Extracting the Private Key from PKCS Keystore🔗

Use OpenSSL to extract the private key from the PKCS keystore when needed. The command shown below extracts the key and saves it to a keystore that is protected using the password you provide:

   $ openssl pkcs12 -in /tmp/hostname-keystore.p12 -passin pass:password \
   -nocerts -out /opt/cloudera/security/pki/hostname.key -passout pass:password

To generate a key without a password, use this version of the command:

  $ openssl rsa -in /tmp/hostname-keystore.p12 -passin pass:password \
   -nocerts -out /opt/cloudera/security/pki/hostname.pem

Converting PEM Key and Certificate to JKS🔗

Replace hostname in the commands below with the FQDN of the host whose certificate is being imported.

Convert the openssl private key and certificate files into a PKCS12 file.

$ openssl pkcs12 -export -in /opt/cloudera/security/pki/hostname.pem \
-inkey /opt/cloudera/security/pki/hostname.key -out /tmp/hostname.p12 \
-name hostname -passin pass:password -passout pass:password

Import the PKCS12 file into the Java keystore.

$ keytool -importkeystore -srckeystore /tmp/hostname.p12 -srcstoretype PKCS12 \
-srcstorepass password -alias hostname -deststorepass password \
-destkeypass password -destkeystore /opt/cloudera/security/jks/hostname-keystore.jks