DRAFT
© 2003 - 2005 Sipura Technology, Inc
Proprietary (See Copyright Notice on Page 2)
18
User Interface
The SPA can be set up such that all outbound calls are secure calls by default, or not secure by default. If
outbound calls are secure by default, user has the option to disable security when making the next call by
dialing *19 before dialing the target number. If outbound calls are not secure by default, user has the
option to make the next outbound call secure by dialing *18 before dialing the target number. On the other
hand, user cannot force inbound calls to be secure or not secure; it is at the mercy of the caller whether
he/she enables security or not for that call.
If the call successfully switches to the secure mode, both parties will hear the “Secure Call Indication
Tone” for a short while and the CID will be updated with the Name and Number extracted from the Mini-
Certificate sent by the other partyThe callee should check the name and number again to ensure the
identity of the caller. The caller should also double check the name and number of the callee to make
sure this is what he/she expects. Note that the SPA will not switch to secure mode if the callee’s CID
Number from its Mini-Certificate does not agree with the user-id used in making the outbound call: the
caller’s SPA will perform this check after receiving the callee’s Mini-Certificate.
Service Provider Requirements
The SPA Mini-Certificate (MC) has a 512-bit public key used for establishing secure calls. The
administrator must provision each subscriber of the secure call service with an MC and the corresponding
512-bit private key. The MC is signed with a 1024-bit private key of the service provider who acts as the
CA of the MC. The 1024-bit public key of the CA signing the MC must also be provisioned to each
subscriber. The CA public key is used by the SPA to verify the MC received from the other end. If the MC
is invalid, the SPA will not switch to secure mode. The MC and the 1024-bit CA public key are
concatenated and base64 encoded into the single parameter <Mini Certificate>. The 512-bit private key is
base64 encoded into the <SRTP Private Key> parameter, which should be hidden from the SPA’s web
interface like a password.
Since the secure call establishment relies on exchange of information embedded in message bodies of
SIP INFO requests/responses, the service provider must maker sure that their infrastructure will allow the
SIP INFO messages to pass through with the message body unmodified.
Sipura provides a configuration tool called gen_mc for the generation of MC and private keys with the
following syntax:
gen_mc <ca-key> <user-name> <user-id> <expire-date>
Where:
- ca-key is a text file with the base64 encoded 1024-bit CA private/public key pairs for signing/verifying
the MC, such as
9CC9aYUEBZmi3AmcqE9U1LxEOGwopaGyGOh3VyhKgi6JaVtQZt87PiJINKW8XQj3B9Qqe3V
gYxWCQNa335YCnDsenASeBxuMIEaBCYd1l1fVEodJZOGwXwfAde0MhcbD0kj7LVlzcsTyk2TZYTccnZ7
5TuTjj13qvYs=
5nEtOrkCa84/mEwl3D9tSvu/Hd+C8u5SNk7hsAUZaA9TqH8Iw0J/IqSrsf6scsmundY5j7Z5mK5J
9uBxSB8t8vamFGD0pF4zhNtbrVvIXKI9kmp4vph1C5jzO9zjypfGUfrpAu
Xb7/k=
- user-name is the name of the subscriber, such as “Joe Smith”. Maximum length is 32 characters
- user-id is the user-id of the subscriber and must be exactly the same as the user-id used in the INVITE
when making the call, such as “14083331234”. Maximum length is 16 characters.
- expire-date is the expiration date of the MC, such as “00:00:00 1/1/34” (34=2034). Internally the date is
encoded as a fixed 12B string: 000000010134
