Key Management - Codes: The Guide to Secrecy from Ancient to Modern Times - page 245

In the message, Alice includes data for Bob, which consists of:

(5) The OI.
(6) The dual signature as in (2) above.
(7) The PIMD as defined in step 1 of the dual signature protocol steps
on page 244. (This is needed by Bob to verify the dual signature, as
we will detail below).
(8) Alice's certificate C A , containing her public signature key, s A . (This
is needed by both Bob and Trent.)

The purchase request message is sent to Bob.

4. Purchase Response Message : Upon receipt of Alice's message, Bob
executes the following steps:

(1) He verifies Alice's certificates via the CA signatures.
(2) He decrypts the dual signature using Alice's public signature key,
thereby verifying that the order has not been altered by any entity
tampering in transit and that it was indeed signed using Alice's pri-
vate signature key.
(3) He processes the OI and forwards the aforementioned data to Trent.
(4) Then Bobsends a purchase response to Alice, which includes acknowl-
edgement of the order appended with the TID; signature of the block
with Bob's private signature key; and Bob's signature certificate.

Upon receipt of the purchase response message, Alice verifies Bob's cer-
tificate, then verifies his signature on the response block. If everything is
valid, her database is updated with this fact.
In the Diagram 6.3, DS stands for dual signature, and the balance of the
acronyms are given above.

Diagram 6.3 Alice's Purchase Request

Initiate Request
−−−−−−−−−−−−→
←−−−−−−−−−−−−−
Initiate Response

Alice Bob

Verify

✞
✝ ✆

✞
✝ ✆

✞
✝ ✆

k A → ✄

✁

to Trent
−−−−−−→
Via Bob

PI + DS + OIMD → e T → Digital Envelope

✂

✄
✂ ✁

to Trent
−−−−−−→
Via Bob

TE

✞
✝ ✆

−−−−−→
to Bob

OI + PIMD + DS + C A