BNB Chain Integrates zk-Fault Proof for opBNB, Enhancing Performance

BNB
Chain
has
announced
the
integration
of
zero-knowledge
(zk)
fault
proofs
for
its
opBNB
protocol.
This
development
aims
to
enhance
the
performance
and
robustness
of
the





blockchain,
according
to
the

BNB
Chain
Blog.

Background
on
zk-Fault
Proof

In
the
past
year,
Optimism
initiated
a
Foundation
Mission
Request
to
develop
the
Op
Stack
Zero
Knowledge
Proof
(ZKP)
for
verifying
the
correctness
of
its
fault
proof
program.
The
ZKP
aims
to
reduce
the
challenge
period
from
7
days
to
12
hours,
avoiding
complicated
interactive
challenge
procedures.
Optimism
funded
three
proposals
from
Risc
Zero,
O(1)
Labs,
and
the
ETH
Storage
team,
all
of
which
proposed
compiling
the
fault
proof
program
into
a
generic
instruction
set
like
RISCV,
WASM,
or
MIPS.

The
compiled
instructions
are
verified
using
zkVMs
such
as
zkRISCV,
zkWASM,
or
zkMIPS.
This
method,
known
as
the
generic
VM
approach,
contrasts
with
a
custom
circuit
approach,
which
BNB
Chain
believes
offers
better
performance.

Development
and
Implementation

Polygon
Zero
recently
developed
a
highly
performant
type1
zkEVM,
aligning
with
BNB
Chain’s
expectations
for
creating
a
custom
circuit
for
opBNB’s
fault
proof
program.
Consequently,
BNB
Chain
developed
a
proof
of
concept
(PoC)
based
on
Polygon
Zero’s
type1
zkEVM
to
demonstrate
performance
advantages
over
the
generic
VM
approach.
The
PoC
is
specific
to
Optimism
and
can
generate
ZKP
for
its
blocks.

The
existing
fault
proof
design
for
Optimism
involves
off-chain
and
on-chain
components,
characterized
by
a
high
gas
cost
and
susceptibility
to
censorship
attacks.
The
zk-fault
proof
aims
to
address
these
issues
by
enabling
challengers
to
submit
just
one
on-chain
transaction,
thereby
reducing
gas
costs
and
shortening
the
challenge
period.

Architecture
of
ZK
Fault
Proof

The
zk-fault
proof
design
comprises
several
components:

• 
  Optimism
  Block
  Execution
  Circuit:
  Processes
  L2
  blocks
  according
  to
  the
  Optimism
  state
  transition
  protocol.
• 
  Optimism
  Block
  Derivation
  Circuit:
  Derives
  L2
  blocks
  from
  L1
  data,
  verifying
  the
  correctness
  of
  the
  derived
  L2
  block.
• 
  Fault
  Proof
  Circuit:
  Validates
  the
  execution
  and
  derivation
  proofs,
  ensuring
  consistency.
• 
  zkFaultProofVerifier
  Contract:
  Resides
  on
  the
  L1
  chain
  to
  verify
  the
  correctness
  of
  the
  ZK
  fault
  proof.

Challengers
can
generate
a
zk-fault
proof
for
disputed
L1
blocks
and
submit
it
to
the
zkFaultProofVerifier
contract.
If
verified,
the
challenger
wins,
reducing
susceptibility
to
censorship
attacks
and
improving
user
experience.

Performance
Testing

BNB
Chain
conducted
performance
tests
comparing
the
opBNB
custom
circuit
with
Zeth
developed
by
Risc
Zero.
The
custom
circuit
proved
more
efficient,
generating
10
times
fewer
ZK
cycles
and
proving
5-6
times
faster
than
Zeth,
making
the
opBNB
approach
5-6
times
cheaper.

Future
Work

The
type1
zkEVM
is
still
in
development,
with
features
like
continuations
aimed
at
making
proof
generation
more
parallel-friendly.
BNB
Chain
plans
to
contribute
to
these
improvements,
expecting
significant
performance
boosts
for
the
opBNB
custom
circuit
approach.

To
complete
the
ZK
fault
proof
for
Optimism
or
opBNB,
additional
components
like
the
block
derivation
circuit,
fault
proof
circuit,
and
on-chain
zkFaultProofVerifier
contract
need
to
be
implemented.
These
tasks
are
slated
for
the
next
phase
of
the
PoC.

Upon
completion,
the
opBNB
team
will
contribute
their
work
to
the
Optimism
ecosystem
to
enhance
the
security
and
performance
of
the
multi-proof
system.

Image
source:
Shutterstock