Add SNIP draft: Pluggable Signer Interface for Smart Accounts

[haycarlitos]

Summary

Adds a Draft SNIP defining a curve-agnostic ISigner trait, a canonical kind-tag registry, and a tagged signature envelope so that one Starknet smart-account class can verify signatures from Phantom (Ed25519), MetaMask (secp256k1 / EIP-191 / EIP-712), passkeys (WebAuthn P-256), hardware wallets (P-256), OAuth providers (JWT-ES256), email (DKIM-RSA), validator keys (BLS12-381), and native STARK wallets — without forking the account contract per curve.

Motivation

Every Starknet account that ships a non-STARK signer today forks a reference implementation and writes curve-specific validation inline, so no two account classes interoperate. The April 2026 security review of the Shhh wallet (report) found three issues (H-2 SRC-5 interface mismatch, M-1 caller-sentinel ambiguity, I-1 custom calls-hash) that all traced to the same root cause: there is no standard way for an account to declare which curve its owner uses. This SNIP is that standard.

It is the authentication-layer companion to the Session Keys SNIP (PR #163, co-authored by @omarespejel), which standardizes authorization. Session keys answer "what may this delegated key do?"; this SNIP answers "which curve is the owner on, and how is it verified?" The two compose into a complete modular-account stack.

What's in the SNIP

• Part A — ISigner trait (verify / kind / validate_pubkey).
• Part B — canonical kind-tag registry. Tier 1: STARK, SECP256K1, ED25519, P256, RSA_2048, BLS12_381. Tier 2: WEBAUTHN_P256, EIP191_SECP256K1, EIP712_SECP256K1, DKIM_RSA, JWT_RS256, JWT_ES256. Tier 3 reserved: ZK_JWT, ZK_EMAIL, ZK_TLS, ZK_TOTP.
• Part C — signature envelope [kind_tag, payload...] so paymasters dispatch without off-chain negotiation.
• Part D — SNIP-9 V2 integration with SNIP-12 typed data as the primary hash.
• Part E — address-salt binding poseidon(primary_kind, owner_commitment) to prevent cross-kind collisions.
• Part F — component / library-call dispatch architecture.
• Part G — SRC-5 discovery.

Non-normative exclusions: TOTP, SMS, passwords — documented as authentication methods that need a ZK envelope to become signers.

Reference implementation

haycarlitos/shhh-wallet-cairo at tag v8.4 (commit 3975532), the V8.4 ShhhAccount declared on Starknet mainnet 2026-05-15:

• Verifier classes (Ed25519, secp256k1, WebAuthn P-256, STARK, and more) dispatched by the account via library_call_syscall.
• Multi-owner storage, deterministic addresses, timelocked governance, guardian recovery, sessions-wallet migration.
• All 12 audit findings from the 2026-04-20 review closed with tested regressions.
• snforge: 259 passing, 0 failing.
• 15 V8.x classes declared on mainnet (~327 STRK cumulative). Class hashes: docs/class-hashes.md.

Linked discussion

• Forum thread (discussions-to): https://community.starknet.io/t/snip-pluggable-signer-interface-for-smart-accounts/116190
• Audit that motivated the SNIP: https://gist.github.com/omarespejel/dddcc2b7df4e8b8bb47af9d1936f8a3e

Note on file name and number

SNIPS/snip-x.md is already occupied by the pending Session Keys SNIP, so this draft is filed as SNIPS/snip-pluggable-signer.md with snip: X in the preamble, pending an editor-assigned number (generally the PR number per SNIP-1). Happy to rename to snip-NNN.md on assignment.

Authors

• Carlos Castillo (@haycarlitos) — Chipi Pay, Shhh wallet
• Omar Espejel (@omarespejel) — co-author, audit reviewer; co-author on the Session Keys SNIP this one stacks on

Status

Draft — open to community review. Not finalized until the reference implementation completes an independent external audit.