Cisco WRP400-G1 Administration Guide - Page 55

Secure Call Details, Message ID 4B

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Secure Call Implementation 3 The signing agent is implicit and must be the same for all ATAs that communicate securely with each other. The public key of the signing agent is pre-configured into the WRP400 by the administrator and is used by the WRP400 to verify the MiniCertificate of its peer. The Mini-Certificate is valid if it has not expired, and it has a valid signature. The WRP400 can be configured so that, by default, all outbound calls are either secure or not secure. If secure by default, the user has the option to disable security when making a call by dialing *19 before dialing the target number. If not secure by default, the user can make a secure outbound call by dialing *18 before dialing the target number. However, the user cannot force inbound calls to be secure or not secure; that depends on whether the caller has security enabled or not. The WRP400 will not switch to secure mode if the CID of the called party from its Mini-Certificate does not agree with the user-id used in making the outbound call. The WRP400 performs this check after receiving the Mini-Certificate of the called party Secure Call Details Looking at the second stage of setting up a secure call in greater detail, this stage can be further divided into two steps. STEP 1 The caller sends a "Caller Hello" message (base64 encoded and embedded in the message body of a SIP INFO request) to the called party with the following information: • Message ID (4B) • Version and flags (4B) • SSRC of the encrypted stream (4B) • Mini-Certificate (252B) Upon receiving the Caller Hello, the called party responds with a Callee Hello message (base64 encoded and embedded in the message body of a SIP response to the caller's INFO request) with similar information, if the Caller Hello message is valid. The caller then examines the Callee Hello and proceeds to the next step if the message is valid. Cisco Small Business WRP400 Administration Guide 53

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Secure Call Implementation
Cisco Small Business WRP400 Administration Guide
53
3
The signing agent is implicit and must be the same for all ATAs that communicate
securely with each other. The public key of the signing agent is pre-configured into
the WRP400 by the administrator and is used by the WRP400 to verify the Mini-
Certificate of its peer. The Mini-Certificate is valid if it has not expired, and it has a
valid signature.
The WRP400 can be configured so that, by default, all outbound calls are either
secure or not secure. If secure by default, the user has the option to disable
security when making a call by dialing *19 before dialing the target number. If not
secure by default, the user can make a secure outbound call by dialing *18 before
dialing the target number. However, the user cannot force inbound calls to be
secure or not secure; that depends on whether the caller has security enabled or
not.
The WRP400 will not switch to secure mode if the CID of the called party from its
Mini-Certificate does not agree with the user-id used in making the outbound call.
The WRP400 performs this check after receiving the Mini-Certificate of the called
party
Secure Call Details
Looking at the second stage of setting up a secure call in greater detail, this stage
can be further divided into two steps.
STEP 1
The caller sends a “Caller Hello” message (base64 encoded and embedded in the
message body of a SIP INFO request) to the called party with the following
information:
•
Message ID (4B)
•
Version and flags (4B)
•
SSRC of the encrypted stream (4B)
•
Mini-Certificate (252B)
Upon receiving the Caller Hello, the called party responds with a Callee Hello
message (base64 encoded and embedded in the message body of a SIP
response to the caller’s INFO request) with similar information, if the Caller Hello
message is valid. The caller then examines the Callee Hello and proceeds to the
next step if the message is valid.