BitVMX: A CPU for Universal Computation on Bitcoin
arxiv(2024)
摘要
BitVMX is a new design for a virtual CPU to optimistically execute arbitrary
programs on Bitcoin based on a challenge response game introduced in BitVM.
Similar to BitVM1 we create a general-purpose CPU to be verified in Bitcoin
script. Our design supports common architectures, such as RISC-V or MIPS. Our
main contribution to the state of the art is a design that uses hash chains of
program traces, memory mapped registers, and a new challenge-response protocol.
We present a new message linking protocol as a means to allow authenticated
communication between the participants. This protocol emulates stateful smart
contracts by sharing state between transactions. This provides a basis for our
verification game which uses a graph of pre-signed transactions to support
challenge-response interactions. In case of a dispute, the hash chain of
program trace is used with selective pre-signed transactions to locate (via
n-ary search) and then recover the precise nature of errors in the
computation. Unlike BitVM1, our approach does not require the creation of
Merkle trees for CPU instructions or memory words. Additionally, it does not
rely on signature equivocations. These differences help avoid complexities
associated with BitVM1 and make BitVMX a compelling alternative to BitVM2. Our
approach is quite flexible, BitVMX can be instantiated to balance transaction
cost vs round complexity, prover cost vs verifier cost, and precomputations vs
round complexity.
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