IEEE Consumer Electronics Magazine - March/April 2020 - 13

Figure 7. Enrollment and authentication steps in the proposed PoP consensus algorithm. (a) Device enrollment steps. (b)
Transaction initiation steps. (c) Device authentication steps.

discussed in detail in the "Physical Unclonable
Functions (PUF) as Hardware Security Primitive" section. The different steps involved in
various phases of the proposed PoP consensus
algorithm are shown in Figure 7.

Device Enrollment Phase
The network of devices using the PUF chain
consensus algorithm is closed to any new devices that have not gone through the enrollment
phase. Initially, a set of challenge inputs are
selected for the PUF module in the new device
and the corresponding responses are generated.
The challenges should satisfy a set of requirements to be considered as inputs to the PUF.
This set of requirements is discussed in the
"Physical Unclonable Functions (PUF) as Hardware Security Primitive" section. The challengeresponse pairs (CRPs) are stored in a secure
database, access to which is granted only to the
trusted nodes in the network.
Initiating a Transaction
Once the device is introduced into the network, data collection starts. The device collects
the data and sends it to the PUF and hashing
module present on the respective device. A challenge input, which is stored in the secure database, is given to the PUF and the response is
generated. This response is added to the block
of data and a hash is generated for the block.
This block then gets broadcast to the network of
devices in PUFchain.

March/April 2020

Device Authentication Phase
The trusted node listens to the message sent
by the client and extracts the data and the hash
from the block. The PUF keys for the corresponding device that broadcast the block are retrieved
from the secure database. Each key is fed to the
PUF and hashing module at the trusted node and
a hash is computed for the data and added the
PUF key. If the hash present in the block and the
generated hash match, the device gets validated
and the block is ready to be added to the blockchain. If the hashes do not match, the procedure
is repeated for all the keys stored for the corresponding device. If none of the hashes match,
the block gets discarded.

PUF AS A HARDWARE SECURITY
PRIMITIVE
PUF is one of the key components in the PUFChain and PoP. A PUF brings out the nanoelectronic manufacturing variations from the devices
on a silicon wafer. The outputs generated by PUF
modules act as a fingerprint to the devices they
are deployed.19

PUF Working Principle
Nanoelectronic manufacturing variations are
introduced into the IC during fabrication process. Due to these, no two devices on an IC are
identical geometrically. Hence, they are used as
PUF modules. Figure 8 elaborates the working
principle of PUF.12,20 Input to a PUF module is
called "challenge" and the output is called
"response." The outputs generated by various

IEEE Consumer Electronics Magazine - March/April 2020

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