Secure Sockets Layer (SSL) certificates are digital certificates that facilitate secure communication between a web server and a client. SSL certificates are issued by Certificate Authorities (CA) and have various extensions such as .pem, .cer, .jks, .pfx, .der, .p12, .crt, and .p7b files. In this article, we will explore how to convert a .cer file to .pem using Keytool.

Understanding Keytool

Keytool is a utility that is part of the Java Development Kit (JDK) and is used to manage cryptographic keys, X.509 certificate chains, and certificate revocation lists (CRL). The tool can be used to create, import, export, and manage keys and certificates. It is a command-line tool that is used to interact with a KeyStore. A KeyStore is a database of cryptographic keys, public key certificates, and secret keys.

Keytool Commands

Before we dive into converting a .cer file to .pem, let’s take a look at some Keytool commands that are commonly used:

• keytool -genkeypair: This command is used to generate a new key pair and stores it in a new KeyStore entry. It prompts the user for a password and generates a new KeyStore if one does not already exist.
• keytool -import: This command is used to import a certificate or a certificate chain into a KeyStore.
• keytool -export: This command is used to export a certificate from a KeyStore.
• keytool -list: This command is used to display the contents of a KeyStore.

Converting CER to PEM

Now that we have a basic understanding of Keytool, let’s explore how to convert a .cer file to .pem using Keytool.

Step 1: Import CER into KeyStore

The first step is to import the .cer file into a KeyStore using the following command:

“`

This command imports the certificate with the alias ‘mycert’ from the file ‘mycert.cer’ into the ‘mykeystore.jks’ KeyStore. The user is prompted for the KeyStore password.

Step 2: Export CER to PEM

The next step is to export the certificate from the KeyStore in PEM format using the following command:

This command exports the certificate with the alias ‘mycert’ from the ‘mykeystore.jks’ KeyStore in PEM format and saves it to the file ‘mycert.pem’. The ‘-rfc’ option specifies that the output should be in Base64-encoded, printable format.

Step 3: Verify PEM File

Finally, verify that the .pem file was created successfully using the following command:

This command displays the contents of the ‘mycert.pem’ file in a human-readable format.

FAQs for Convert Cer to Pem Keytool:

What is a CER file?

A CER file is a certificate file that typically contains a public key for a server or client certificate. It is usually used for verifying the identity of the certificate owner in secure communication protocols like HTTPS, TLS, and SSL.

What is a PEM file?

A PEM file is a base64-encoded ASCII file format used for storing security certificates. It contains a public key or a private key or both. PEM files can also contain certificate chains, which are multiple certificates that create a chain of trust.

How do I convert CER to PEM using Keytool?

You can convert a CER file to PEM format using Keytool in the following steps:
1. Open the command prompt.
2. Navigate to the directory where Keytool is installed.
3. Use the following command to convert the CER file to PEM format:
keytool -import -noprompt -file yourcert.cer -alias youralias -keystore yourkeystore.jks -storepass yourpassword
4. Extract the certificate using the following command:
keytool -exportcert -keystore yourkeystore.jks -alias youralias -rfc -file yourcert.pem -storepass yourpassword
5. Now you will have a PEM format certificate file, which you can use for secure communication.

Can I convert multiple CER files to PEM files using Keytool?

Yes, you can convert multiple CER files to PEM format using Keytool. Use the following command:
for %f in (*.cer) do keytool -import -noprompt -file %f -alias %~nf -keystore yourkeystore.jks -storepass yourpassword && keytool -exportcert -keystore yourkeystore.jks -alias %~nf -rfc -file %~nf.pem -storepass yourpassword
This command will convert all the CER files in the directory to PEM format and store them in the same directory.

Is Keytool the only way to convert CER to PEM?

No, you can convert CER to PEM format using other tools as well. OpenSSL is one such tool that can be used to convert the certificate format. You can use the following command to convert the CER file to PEM format using OpenSSL:
openssl x509 -inform der -in yourcert.cer -out yourcert.pem
This command will convert the CER file to PEM format and store it in the same directory.