Can not generate self-signed certificate

Platform on Aegir 3.12 (7.x-3.12.0)

Enabled modules:

• Aegir Certificate Service
• Aegir HTTPS
• Aegir HTTPS Apache
• Aegir Self-signed Service

I've followed the installation instructions and server and site set-up in the README file.

After enabling encryption, verify site fails. Log messages:

generating 2048 bit RSA key in /var/aegir/config/self_signed.d/example.com/

failed to generate signing request for certificate in /var/aegir/config/self_signed.d/example.com/openssl.csr

failed to generate self-signed certificate in /var/aegir/config/self_signed.d/example.com/openssl.crt