How to point OpenSSL to the root certificates on an Android device?

Pointing OpenSSL to Root Certificates on Android

OpenSSL, a powerful command-line tool for managing and using SSL/TLS certificates, can be leveraged on Android devices to perform various security tasks. This article will guide you on how to configure OpenSSL to utilize the root certificates installed on your Android device.

Understanding Root Certificates

Root certificates are the foundation of trust in the SSL/TLS ecosystem. They are issued by trusted Certificate Authorities (CAs) and serve as the starting point for verifying the authenticity of websites and other entities.

Location of Root Certificates

Android devices store root certificates in a system-wide trust store. The exact location of this trust store can vary depending on the Android version and device manufacturer.

Typically, the trust store can be found in the following directories:

• /system/etc/security/cacerts
• /system/etc/security/trusted-cert

Using OpenSSL on Android

Method 1: Using Termux

Termux is a popular Android terminal emulator that provides a Linux-like environment, allowing you to use OpenSSL and other command-line tools.

Steps

1. Install Termux from the Google Play Store.
2. Open Termux and update the package list: pkg update
3. Install OpenSSL: pkg install openssl
4. Verify the installation: openssl version
5. Set the environment variable OPENSSL_CONF to point to the trust store directory:

export OPENSSL_CONF="/system/etc/security/cacerts"

6. Run your desired OpenSSL command, e.g., verifying a certificate:

openssl s_client -connect example.com:443 -showcerts

Method 2: Using a Root Certificate Bundle

You can create a bundle of root certificates from the Android trust store and use it with OpenSSL.

Steps

1. Use the keytool command to extract the root certificates from the trust store. For example:

keytool -list -keystore "/system/etc/security/cacerts" -storepass android

2. The command output will list the certificates. Note the aliases of the desired certificates.
3. Extract the certificates using keytool:

keytool -exportcert -alias "certificate_alias" -keystore "/system/etc/security/cacerts" -storepass android -file "certificate.pem"

4. Combine the extracted certificates into a single bundle file, e.g., using cat:

cat certificate1.pem certificate2.pem > root_certs.pem

5. Use the bundle file with OpenSSL:

openssl s_client -connect example.com:443 -CAfile root_certs.pem -showcerts

Troubleshooting

If you encounter issues while pointing OpenSSL to the root certificates, consider the following:

• Verify the location of the trust store on your device. It may differ from the typical locations mentioned above.
• Check the permissions of the trust store directory and ensure OpenSSL has access to it.
• If using a certificate bundle, make sure the certificates are properly formatted and included in the bundle file.

Conclusion

By following these steps, you can successfully point OpenSSL to the root certificates on your Android device. This enables you to perform various security tasks, including certificate verification, trust store management, and more.