Keys and Certificate Storage in Cisco IP Telephony

Key storage is a major part of key management because an improperly stored key can enable an attacker to compromise parts of the PKI or the whole PKI. The IP phone stores its public and private RSA keys and its certificate in its nonvolatile memory. This information is preserved across phone reboots and resets. The keys cannot be extracted from the IP phone unless the phone is taken apart and the nonvolatile memory is then physically analyzed.

The IP telephony servers (Cisco CallManager, CAPF, and TFTP server) store certificates on the local hard disk, in a special area called the Microsoft certificate store. The private key of the server is stored in the private-key storage. The private-key storage is protected by the periodically changed master key. The master key itself is encrypted with Triple Data Encryption Standard (3DES) using a key derived from the password of the user.

Microsoft Windows XP stores a certificate locally on the computer or device that requested it or, in the case of a user, on the computer or device that the user used to request it. The storage location is called the certificate store.

The Cisco CTL client stores its public and private RSA keys on the security tokens supplied by Cisco. The keys are embedded on the token during production, and the token is designed never to leak these keys from its memory.