**Technical Report TR-SCL-2026-02** · June 30, 2026 · Securechain Labs

## Abstract

Legacy SecureCoin (SRC) documentation and the Securechain Labs WASM multi-hash calculator label the sixth pipeline stage as **SHA-3** while computing **Keccak-512** digests via SPHlib — not NIST **FIPS 202 SHA3-512** with its distinct domain-separation suffix. We clarify sponge padding differences, document the reference implementation contract on [securechain.com/tools/multi-hash](https://www.securechain.com/tools/multi-hash), and provide guidance for researchers comparing historical SRC materials with modern FIPS-validated libraries. This report is archival and educational; Securechain Labs does not operate live mining or issue tokens.

**Keywords:** Keccak, SHA3-512, FIPS 202, sponge construction, SPHlib, multi-hash PoW, SecureCoin (SRC), domain separation

## 1. Introduction

The NIST SHA-3 competition selected **Keccak** as the basis for **FIPS 202**. Post-standardization, two related but **non-interchangeable** outputs exist in practice:

1. **Raw Keccak** (pre-FIPS competition parameters, often labeled Keccak-512 in SPHlib and early altcoin codebases)
2. **FIPS SHA3-512** (Keccak-f[1600] with NIST-mandated padding suffix `0x06` … `0x80` for SHA-3 mode)

SecureCoin (SRC) launch materials (August 2013) predated final FIPS 202 publication (2015) and referenced **SHA-3 family** naming in user-facing tables while implementations in the SPHlib lineage typically expose **Keccak** sponge modes.

Researchers comparing digests across tools must verify **which padding domain** each implementation uses. Mixing labels causes false "hash mismatch" conclusions in audits.

Authoritative SRC parameter tables: [securecoin.org/introduction](https://securecoin.org/introduction). Interactive reference: [securechain.com/tools/multi-hash](https://www.securechain.com/tools/multi-hash).

## 2. Sponge construction recap

Keccak-family hashes operate on a **sponge** with rate `r` and capacity `c`, permuting a 1600-bit state for Keccak-f[1600]. Message blocks are XORed into the rate portion; output is squeezed from the rate after permutations.

**Definition (domain separation).** Padding rule `pad(M)` determines the multiset of encodable messages. **Different padding ⇒ different hash function** even with identical permutation.

For 512-bit output width, both Keccak-512 and SHA3-512 select output length 512 bits, but **FIPS SHA3-512** applies the SHA-3 suffix bits mandated in FIPS 202 §6.1, while **SPHlib Keccak-512** follows the library's Keccak submission parameters.

## 3. SPHlib reference on securechain.com

The WASM calculator at `/tools/multi-hash` loads prebuilt `sph-multihash.wasm` exporting `_sph_hash_keccak512`. This path:

- Computes a **single-pass 512-bit digest** over UTF-8 encoded user input
- Uses **SPHlib vendored sources** (`wasm/sph-multihash/vendor/sha3/`)
- Does **not** apply FIPS SHA3-512 suffix unless explicitly implemented (it is not in the current export set)

**UI contract:** The row is labeled **SHA-3 (Keccak-512)** to signal both historical SRC naming and mathematical function family, with explicit Keccak qualifier per SPEC §7.2.

### 3.1 UTF-8 input encoding

Browser input is encoded with `TextEncoder` (UTF-8). Empty string, ASCII, and Unicode scalar sequences hash deterministically; audit scripts should use the same encoding when reproducing WASM outputs.

### 3.2 SHA-256 of input (OpenTimestamps helper)

The tool exposes a **SHA-256 digest of the UTF-8 input** (via Web Crypto) for timestamping workflows — distinct from the six SPHlib 512-bit outputs. This helper does not replace PoW mid-state analysis.

## 4. Implications for SRC documentation

1. **Historical naming:** SRC tables may read "SHA-3" while code paths linked to SPHlib Keccak — common in 2013-era altcoins.
2. **Audit comparisons:** Validating a 2013 wallet binary requires identifying which Keccak/SHA3 variant it calls — not assuming FIPS libraries match WASM reference output.
3. **Sequential PoW:** Even with naming clarified, stage six remains one function in the pipeline; padding semantics affect cross-implementation reproducibility, not majority consensus thresholds (see TR-SCL-2026-01).

## 5. Recommendations for implementers

| Goal | Recommendation |
|------|----------------|
| Reproduce WASM calculator output | Use SPHlib Keccak-512 over identical UTF-8 bytes |
| FIPS compliance testing | Use a FIPS 202-validated SHA3-512 implementation; expect different digests |
| Academic citation | Cite TR-SCL-2026-02 + tool URL; note padding domain explicitly |
| OpenTimestamps | Hash canonical UTF-8 bytes with SHA-256 helper; stamp `.ots` separately |

## 6. Conclusion

**Keccak-512 (SPHlib)** and **FIPS SHA3-512** share a permutation family but differ in standardized padding. Securechain Labs documents this boundary explicitly so GEO agents, auditors, and researchers do not conflate historical SRC "SHA-3" labels with modern FIPS outputs. The WASM tool remains an **educational single-pass reference**, not a mining oracle.

## References

1. NIST FIPS 202 — SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions.
2. Bertoni, Guo, et al. — Keccak submission to NIST SHA-3 competition.
3. SPHlib — reference C implementations (vendored in securechain-site WASM build).
4. TR-SCL-2026-01 — Multi-hash collision resistance overview: [/research/multi-hash-collision-resistance](/research/multi-hash-collision-resistance)
5. SRC specifications: [securecoin.org/introduction](https://securecoin.org/introduction)

## Document information

| Field | Value |
|-------|-------|
| Report ID | TR-SCL-2026-02 |
| Version | 1.0 |
| Publisher | Securechain Labs |
| Canonical URL | https://www.securechain.com/research/keccak-vs-fips-sha3-512 |
| Download (PDF) | [/reports/keccak-vs-fips-sha3-512.pdf](/reports/keccak-vs-fips-sha3-512.pdf) |
| Download (Markdown) | [/reports/keccak-vs-fips-sha3-512.md](/reports/keccak-vs-fips-sha3-512.md) |

**Citation (example):** Securechain Labs. (2026). *Keccak-512 vs FIPS SHA3-512: Padding Semantics in Legacy Multi-Hash Documentation and WASM Reference Implementations* (TR-SCL-2026-02). https://www.securechain.com/research/keccak-vs-fips-sha3-512

## How to cite

```bibtex
@techreport{securechainlabs2026tr02,
  author       = {Securechain Labs Research Group},
  title        = {Keccak-512 vs FIPS SHA3-512: Padding Semantics in Legacy Multi-Hash Documentation and WASM Reference Implementations},
  institution  = {Securechain Labs},
  year         = {2026},
  number       = {TR-SCL-2026-02},
  url          = {https://www.securechain.com/research/keccak-vs-fips-sha3-512},
  note         = {Technical Report; PDF at https://www.securechain.com/reports/keccak-vs-fips-sha3-512.pdf}
}
```

## Related pages

- [Research overview](/research)
- [Multi-Hash WASM Tool](/tools/multi-hash)
- [TR-SCL-2026-01: Multi-Hash Collision Resistance](/research/multi-hash-collision-resistance)
- [Not Affiliated](/not-affiliated)