> For the complete documentation index, see [llms.txt](https://docs.zetrix.com/en/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.zetrix.com/en/developer-resources/agentic-wallet/architecture/crypto-architecture-split.md).

# Crypto architecture split

Standard HSMs cannot derive the zero-knowledge / selective-disclosure proofs (BBS+, Bulletproof range-proofs) that privacy-preserving VCs require. Responsibilities therefore split:

| Operation                                                           | Where it runs                                                                           |
| ------------------------------------------------------------------- | --------------------------------------------------------------------------------------- |
| Selective-disclosure proof derivation (BBS+, range-proofs) from VCs | **Software**, inside the Agentic Wallet MCP                                             |
| Holder-binding signature (Ed25519 over the request nonce)           | **SoftHSM** holder key (PKCS#11), via the Wallet BE — password-gated, no session tokens |
| x402 payment blob signing (blob unsigned until HSM signing)         | **SoftHSM** holder key, via the Wallet BE                                               |
| Issuer signature (VC issuance)                                      | **MBI / MYID issuer** — Ed25519 + BBS+                                                  |
| In-process VP verification (signature, BBS+, range-proof, DCQL)     | **OID4VP Verifier**                                                                     |
| Issuer public-key resolution                                        | **On-chain ZID Registry** (direct read)                                                 |

Private keys never leave the SoftHSM / Wallet BE boundary; the MCP requests signatures, it does not hold signing keys. The x402 payment blob is assembled unsigned and only signed at the HSM step.