Exam CAS-004 topic 1 question 277 discussion

Using the iOS keychain to store your private key has the added security advantage of leveraging on the hardware-backed keystores that exist on many iOS devices, allowing the key to be protected by the iOS-level device password, and preventing key compromise even if the device is rooted. If you already have your client certificate and private key bundled into a PKCS#12 file (extension .p12 or .pfx), you can import it into the app private section of the iOS Keychain using Mail, Safari or iTunes. Note sure that the file extension has to be changed to .ovpn12 for the file to be picked up by the OpenVPN Connect App (and not by iOS). Note that on iOS, when you import a PKCS#12 file into the Keychain, only the client certificate and private key are imported. The CA (certificate authority) certificates are NOT imported (unless you manually extract the CA certificates and import them separately, one-at-a-time). Therefore, the CA list must be given in the profile using the ca directive. If you already have a PKCS#12 file, the CA list may be extracted from the file using this openssl command, where the CA certs in client.p12 are written to ca.crt:

o CA certificate is crucial: A root certificate chain includes the intermediate certificates that authenticate the issuing Certificate Authority (CA). The VPN client needs the root CA certificate to verify the authenticity of the server certificate presented by the VPN server. o Import issue on iOS: When importing a .p12 file on iOS, the device might only extract the client certificate information (public and private keys) and not the associated root CA certificates, leading to the "ca certificate is undefined" error. o Why other options are less likely: o A. iOS devices have an empty root certificate chain by default: While iOS devices have a pre-installed set of trusted root certificates, they are generally not empty. This is because iOS needs these certificates to verify system updates, app installations, and other secure connections. If the root chain was completely empty, no secure connections would be possible on the device.

Certificate Chain: When connecting to a VPN service that requires client certificates, iOS devices need to have the complete certificate chain, including the Certificate Authority (CA) certificate, in order to verify the authenticity of the server's certificate during the TLS handshake. PKCS#12 File (PFX): A .p12 file (or PFX format) typically contains both the client certificate and its associated private key, and optionally the CA certificate chain. D. The iOS keychain imported only the client public and private keys: While this could cause a different set of errors related to missing keys, it does not directly address the "ca certificate is undefined" error, which specifically relates to the CA certificate chain.

The error "mbedTLS: ca certificate is undefined" on iOS devices when using a VPN service with client certificates points to the absence of CA certificates in the iOS Certificate Trust Store. To resolve this issue, ensure that the .p12 certificate file imported into the iOS device includes the necessary CA certificates along with the client's certificate and private key, or manually install the CA certificates into the iOS device's trusted root store. This will allow the device to verify the authenticity of the VPN server during the connection establishment process.

QUESTION STATES: Which of the following is the root cause of this issue? While A and D are both independently true statements: option A explains why the error occurred [root cause] option D explains potential recent contribution, but A is already true