A User Centric Security Model for Tamper-Resistant Devices

A.4 ASPeCT Protocol
A.4 ASPeCT Protocol
The ASPeCT protocol is designed as part of the European Commission ACTS project
ASPeCT [232], which focuses on the mobile network environment for value-added transactions.
Earlier versions of the ASPeCT protocol is proposed in Martin et al. [176], and
Horn and Preneel [177]. However, in this section we describe the protocol as it is detailed
in the Horn et al. [168]. Additional notations required for the description of the ASPeCT
are as below:
ID T identier of the smart card's certication authority.
CertSt certied (static) public key agreement key (g SP ) of the SP.
h1, h2, h3 one-way hash functions, that are detailed in Horn and Preneel [177].
cd details of the charging data.
T S time stamp.
py payment conrmation.
ASPeCT-1. SC → SP : g SC ||ID T
SP : k SC−SP = h1(N SP ||(g SC ) SP )
The SC generates a Die-Hellman exponential g SC and append it with the identity of the
smart card's certication authority (ID T ). On receipt of this message, the SP generates
the shared secret key by using the g SC , public key agreement key g SP along with a random
number generated by the SP .
ASPeCT-2. SP → SC : N SP ||h2(k SC−SP ||N SP ||S i )||CertSt
SC : k SC−SP = h1(N SP ||(g SP ) SC )
SC : H = h3(g SC ||g SP ||N SP ||ID SP ||cd||T S||py)
In response, the SP adds the random number N SP appended with the hash generated by
the function h2 on the generated key (for key authentication), N SP , and identity of the
SP. Finally, appending the certicate of the public key agreement key (e.g. g SP ).
On reception of the second message, the SC retrieves the public key agreement key (g SP )
and then follow the similar steps like SP to generate the shared secret key. After generating
the k SC−SP , the SC will authenticate the shared key by generating the hash with function
h2 and match with the one received in the message 2. If it matches then SC got the key
authentication from the SP.
The SC will then generate the transaction that includes the several elements from the
rst two message along with the charging details associated with the particular SC, which
contains the time stamp and payment details (py). All these elements are then hashed
using the function h3 and the output is referred as H.
ASPeCT-3. SC → SP : e kSC−SP (Sign SC (H)||CertS SC , py)
In response, the SC will sign the H (that is used as non-repudiation of the transaction).
It then appends the signature key certicate for the SC and payment details. The entire
message is then encrypted by the shared secret key.
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