A User Centric Security Model for Tamper-Resistant Devices

6.5 Application Acquisition and Contractual Agreement Protocol
STCP ACA -1. SP : SI = f kSP (g r SP
||N SP ||SC IP )
SP → SC : SP i ||N SP ||g r SP
||SP Sup ||V R||ALP ||SI
SC : K = (g r SP
) r SC
mod p
SC : k SC−SP = H K (N SP ||N SC || ′ 1 ′ )
SC : mk SC−SP = H K (N SP ||N SC || ′ 2 ′ )
The SP will initiate the STCP ACA by generating a random number (N SP ) and Die-
Hellman exponential (g r SP ). It appends the generated values with the SPSup and associated
ALP.
When the SC receives the message, it check whether it can meet the SP's ALP and support
features from the SP Sup list. The SC will then generate the shared secret and required
session encryption and MAC keys.
STCP ACA -2. SC : hs = h(SC i ||SP i ||g r SC
||g r SP
||N SC ||N SP )
SC : AU SC = Sign SC (V M||SC i ||SP i ||hs)
SC : mE = ek SC−SP (AU SC ||OP ||CertS SC )
SC → SP : N SC ||g r SC
||SC Config ||mE||f mkSC−SP (mE)||SI
The SC will generate a random number (N SC ) and Die-Hellman exponential (g r SC ).
Subsequently, the SC will proceed with generating the AU SC and may include V M depending
upon the SP's requirement (e.g. online or oine attestation) pointed out in the
SP Sup . If the SP is a member of the AD syndicate, the SC will include an OP containing
the certicate issued to the SC by the AD. Each SC has a list of members associated
with the respective AD, which can be regularly updated by the AD.
On receipt of the STCP ACA -2, the SP will rst verify the session cookie and the SC's
capabilities listed in SC Config . The SP will then generate the shared secret and session
keys similar to the SC. Subsequently, it will verify the MAC and decrypt the message.
The SP then veries the generated signature and V M (if required); if successful the SP
will proceed with the protocol.
STCP ACA -3. SP : hp = h(SP i ||SC i ||g r SC
||g r SP
||N SC ||N SP )
SP : AU SP = Sign SP (SP i ||SC i ||App i ||hp)
SP : mE = ek SC−SP (AU SP ||CertS SP ||OC)
SP → SC : mE||f mkSC−SP (mE)||SI
The SP will generate an encrypted and MACed message that contains AU SP , SP's certicate,
and an optional certicate OC. The optional certicate eld is used by the SP if its
application also has a third party evaluation certicate (AAC: section 4.4.2). The AU SP
includes the identities of the SP and the respective application along with hp.
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