The Verification Crossroads: Tracing the PSProve PoRep Bug Through ffi.VerifySeal

In the midst of a sprawling investigation into a PSProve PoRep CuZK failure, a single message from the assistant captures a pivotal moment of analytical focus. Message [msg 1663] is deceptively simple on its surface: a lone read tool call that retrieves the VerifySeal function from /tmp/czk/extern/filecoin-ffi/proofs.go. But this message is not about reading code—it is about the reasoning that drove the assistant to that particular file at that particular moment, and the subtle shift in investigative strategy it represents.

The Investigation So Far: A Landscape of Ruled-Out Hypotheses

To understand why message [msg 1663] matters, one must first appreciate the investigative journey that preceded it. The assistant had been systematically tracing a bug where PSProve PoRep proofs generated via the CuZK GPU proving engine failed verification (ffi.VerifySeal returned false), while the same proofs generated through the standard FFI (Foreign Function Interface) path worked correctly. This was a high-stakes debugging session: CuZK is a custom GPU-accelerated proving system, and a failure in its PSProve integration threatened the viability of the entire proof outsourcing marketplace.

By the time we reach message [msg 1663], the assistant had already eliminated an impressive list of potential causes. Enum mappings between Go, C, and Rust had been verified as identical. The JSON struct fields used in serialization had been compared field-by-field and found to match perfectly. The make_prover_id function in CuZK's Rust code had been confirmed to produce identical output to Go's toProverID function, both using LEB128/varint encoding. The wrapper format wrapping the C1 output was identical between paths. And the data flow through the proofshare system had been traced and found to be free of corruption.

Each of these ruled-out hypotheses represents hours of careful code reading, cross-referencing, and reasoning. The assistant had built a mental model of the entire data flow—from C1 output generation through JSON serialization, through the proofshare upload and fetch pipeline, through CuZK's deserialization and SNARK generation, and finally through Go-side verification. With each ruled-out cause, the space of remaining possibilities narrowed.

The Critical Shift: From Generation to Verification

Message [msg 1662], which immediately precedes our target message, reveals the assistant's thinking at a crucial inflection point. The assistant had been comparing the FFI path and the CuZK path for SealCommitPhase2, noting that both pass sectorId and proverId as separate arguments to the underlying Rust function. But then the assistant makes a critical observation:

"The critical thing is that the SNARK public inputs include the prover_id and sector_id. If these differ between generation and verification, the proof fails."

This insight reframes the entire investigation. Up to this point, the assistant had been focused on whether CuZK correctly generates the SNARK. But CuZK was successfully returning a proof—the SNARK generation itself was not failing. The failure occurred later, when Go-side ffi.VerifySeal declared the proof invalid. This meant the problem was not in SNARK generation per se, but in a mismatch between the public inputs used during generation and those used during verification.

The assistant's next sentence reveals the logical next step: "Let me check what ffi.VerifySeal does and compare." This is the motivation for message [msg 1663]. The assistant needs to see the exact inputs that VerifySeal uses, to compare them against what CuZK used during SNARK generation.

What Message 1663 Actually Contains

The message itself is straightforward. The assistant issues a read tool call targeting /tmp/czk/extern/filecoin-ffi/proofs.go, requesting the content of the file. The output shows the beginning of the VerifySeal function:

[assistant] [read] /tmp/czk/extern/filecoin-ffi/proofs.go
<path>/tmp/czk/extern/filecoin-ffi/proofs.go</path>
<type>file</type>
<content>25: 	"github.com/filecoin-project/filecoin-ffi/cgo"
26: )
27: 
28: // VerifySeal returns true if the sealing operation from which its inputs were
29: // derived was valid, and false if not.
30: func VerifySeal(info proof.SealVerifyInfo) (bool, error) {
31: 	sp, err := toFilRegisteredSealProof(info.SealProof)
32: 	if err != nil {
33: 		return false, err
34: 	}
35: 
36: 	commR, err := to32ByteCommR(info.SealedCID)
37: 	...

The function signature reveals that VerifySeal takes a proof.SealVerifyInfo struct, which contains all the verification parameters: SealProof (the proof type), SealedCID (from which CommR is derived), UnsealedCID (from which CommD is derived), Miner (from which ProverID is derived), Randomness (the ticket), InteractiveRandomness (the seed), and SectorID.Number. The function extracts each of these and passes them to the underlying C FFI for verification.

The Reasoning Behind the Read

The assistant's decision to read VerifySeal is driven by a specific hypothesis: that the public inputs used during CuZK's SNARK generation might differ from those used during Go-side verification. This is a classic class of cryptographic bug—if the prover and verifier disagree on even a single byte of the public inputs, the proof will fail verification even though it was correctly constructed.

The assistant had already confirmed that make_prover_id in CuZK matches toProverID in Go, so prover_id derivation was not the issue. But there were other inputs to consider: comm_r, comm_d, the ticket (randomness), the seed (interactive randomness), and the sector number. Any of these could potentially differ between the two paths.

Crucially, the assistant was operating under a specific assumption: that CuZK's SNARK generation used values extracted from the deserialized C1 output JSON, while Go-side verification used values from the original in-memory Commit1OutRaw struct. If the JSON round-trip had altered any of these values—even in a byte-order or encoding subtlety—the SNARK would be generated for the wrong public inputs, and verification would fail.

This is a sophisticated debugging intuition. The assistant recognized that the bug might not be in the SNARK generation logic at all, but in the data pipeline feeding it. The JSON serialization/deserialization round-trip was the only variable that differed between the working FFI path (which passed raw Rust JSON bytes directly) and the failing CuZK path (which re-serialized from a Go struct).## Assumptions Embedded in the Investigation

Message [msg 1663] reveals several implicit assumptions that shaped the assistant's investigative approach. First, the assistant assumes that the VerifySeal function is the authoritative source of truth for what inputs matter. This is a reasonable assumption—the function is part of the Filecoin FFI specification and represents the canonical verification logic. But it also means the assistant is implicitly trusting that the verification logic itself is correct and that any mismatch must be in the data fed to it.

Second, the assistant assumes that the JSON round-trip is the most likely source of discrepancy. This is evident from the reasoning in the surrounding messages, where the assistant repeatedly returns to the question of whether json.Marshal followed by serde_json::from_slice produces identical byte representations. The assistant had already identified that the Commit1OutRaw struct in Go and the SealCommitPhase1Output struct in Rust had identical fields, but the question of whether the values survived the round-trip unchanged remained open.

Third, the assistant assumes that CuZK's SNARK generation is internally consistent—that if it produces a proof, the proof is valid for the inputs it used. This is a necessary assumption for the debugging strategy: if CuZK were producing invalid proofs even for correct inputs, the debugging approach would need to be entirely different. The fact that normal (non-PSProve) CuZK PoRep proofs work correctly supports this assumption.

Input Knowledge Required

To fully understand message [msg 1663], one needs substantial domain knowledge about the Filecoin proof system. The reader must understand what SealCommitPhase1 and SealCommitPhase2 are—the two phases of the sealing operation that generate a proof of replication (PoRep). Phase 1 produces a "vanilla proof" (the C1 output), and Phase 2 converts this into a Groth16 SNARK (the C2 output). The VerifySeal function then checks the SNARK against the original public parameters.

One must also understand the architecture of the CuZK system: a GPU-accelerated proving engine that replaces the standard CPU-based FFI for Phase 2. CuZK accepts the same C1 output JSON but uses GPU parallelism to generate the SNARK much faster. The PSProve (ProofShare Prove) system is a marketplace where miners can outsource proof generation to specialized provers.

The reader also needs to understand the concept of public inputs in Groth16 proofs. A SNARK proves knowledge of a witness satisfying a constraint system, but it is bound to specific public inputs. If the prover and verifier disagree on these inputs, the proof fails—even if the prover correctly followed the protocol. This is the core insight driving the assistant's investigation.

Output Knowledge Created

Message [msg 1663] itself produces limited direct output—it simply reads a file. But the knowledge it creates is in the context it provides for subsequent reasoning. The assistant now has the exact interface of VerifySeal and can trace each input back through the code to see where it originates.

This reading enables the assistant to construct a precise mapping between CuZK's SNARK generation inputs and VerifySeal's verification inputs. In the messages that follow ([msg 1664]), the assistant explicitly lists the inputs used by VerifySeal and compares them against what computePoRep sends to CuZK. This comparison reveals that all inputs appear consistent—sector ID, miner ID, randomness, seed, comm_r, and comm_d all derive from the same sources.

The real output knowledge, however, is the narrowing of the hypothesis space. By confirming that the public inputs are consistent between generation and verification, the assistant eliminates another class of potential causes. This forces a deeper examination of the JSON serialization itself—specifically, whether the byte-level representation of the C1 output changes during the Go round-trip in ways that affect CuZK's internal processing.

The Thinking Process in Action

What makes message [msg 1663] fascinating is what it reveals about the assistant's thinking process. The assistant is engaged in a form of differential diagnosis, systematically ruling out potential causes by tracing the data flow and comparing paths. Each read operation is driven by a specific hypothesis, and the results either confirm or eliminate that hypothesis.

The assistant's reasoning shows a sophisticated understanding of the system architecture. Rather than guessing randomly, the assistant traces the exact path of each byte from source to destination, comparing the working and failing paths at each step. The question "what does ffi.VerifySeal do and compare" reveals a search for the exact point where the two paths diverge.

There is also a notable intellectual humility in the assistant's approach. Despite having ruled out numerous potential causes, the assistant remains open to the possibility that the bug is something entirely unexpected. The repeated returns to the JSON round-trip hypothesis—even after establishing that the struct fields match—show a willingness to question assumptions and dig deeper.

Conclusion

Message [msg 1663] represents a turning point in the PSProve PoRep investigation. By reading the VerifySeal function, the assistant shifts focus from SNARK generation to the verification interface, recognizing that the bug might lie in a mismatch between what CuZK thinks it proved and what Go-side verification expects. This reframing is a classic debugging maneuver—when the output is correct but rejected, look at the acceptance criteria.

The message also exemplifies the assistant's methodical approach to debugging complex distributed systems. Each read operation is purposeful, driven by a specific hypothesis. Each piece of evidence is weighed against the accumulated knowledge from previous investigations. And when the evidence rules out a hypothesis, the assistant pivots gracefully to the next most likely cause.

In the broader context of the conversation, this message is one step in a long chain of reasoning that eventually leads to the root cause. But it is a crucial step—one that demonstrates how careful, hypothesis-driven investigation can systematically narrow the space of possibilities until the bug has nowhere left to hide.