> For the complete documentation index, see [llms.txt](https://shinkalabs.gitbook.io/hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://shinkalabs.gitbook.io/hub/andromeda/on-chain-programs/challenges.md).

# Domain-separated challenges

Every wallet-agnostic action signs a fixed 32-byte challenge. The challenge is not just a random nonce: it is a domain-separated digest that binds the action's identity into the bytes the user signs, so a signature gathered for one action cannot be replayed for another.

## What goes into a challenge

A challenge is a hash over, in order:

```
"andromeda::rules-policy::v1"   domain tag (version-pinned)
op-tag                          which operation this is
dwallet                         the dWallet address it concerns
... operation-specific fields   (for example, the message hash)
nonce                           the per-flow replay nonce
member-or-primary slot          the 34-byte slot of the signer
```

So a primary-recovery challenge for dWallet A at nonce 7 hashes to something different from a quorum-contribution challenge for the same dWallet, a different member, or a different nonce. Reusing a signature across actions does not work, because the bytes that were signed do not match what the program recomputes.

## Why a domain tag

The leading domain string (`andromeda::rules-policy::v1`) ensures these challenges can never collide with bytes a wallet might sign for something else, and the `v1` makes the construction explicit so it can evolve without ambiguity.

## How many

There are fourteen distinct challenge constructions in the `rules-policy` program, one per kind of action (primary recovery, the various admin changes, opening a quorum session, contributing to one, finalising, closing, and so on). Each is implemented in the Rust program and mirrored byte-for-byte in the TypeScript that the engine uses to build the `challenge` responses, so what the client signs is exactly what the program will recompute and verify.

## What this means for client builders

If you build something that constructs challenges yourself rather than calling the `challenge` endpoint:

* You must reproduce the exact byte layout, including the domain tag, the operation tag, the field order, the nonce, and the 34-byte member slot.
* You must use the nonce the program currently expects (read it from the chain or from a `challenge` response).
* Getting any of this wrong produces a signature the program rejects.

In practice, calling the `challenge` endpoint and signing what it returns is the supported path. The construction is documented here so the behaviour is auditable, not so you have to reimplement it.

## Replay protection beyond the challenge

The challenge binds the nonce, and the program tracks the nonce on-chain (`next_admin_nonce`, `next_primary_recover_nonce`, `next_session_nonce`), incrementing it as actions succeed. So even a correctly constructed challenge is single-use: once the action runs, the nonce moves and that exact challenge can never be valid again.


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