# Deterministic Secret Management

When making transactions the user needs to come up with various secrets: `trapdoor`, `nullifier`  which all must be stored (or at least the most recent one) in order to keep using the shielder. Backing up so many secrets is problematic hence we introduce a deterministic secret management scheme that allows the user to keep just one secret seed and derive all the remaining secrets out of it. 

The simplest attempt at such a scheme could be as follows:

* The user starts by generating a master seed: `seed` with say 256 bits,
* The user generates its ZK-ID: `id = hash(seed, "id")` 
* Whenever a new secret is required, for instance nullifier, it is derived as
  * `nullifier = hash(seed, "nullifier-X")` where `X` is a unique nonce, for instance the index of the transaction or so,
  * `trapdoor = hash(seed, "trapdoor-X")` 
  * similarly for the case of generating randomness for the sake of encryption or `mac` -- special care must be taken to never reuse the same randomness, because it is revealed right away (recall that `mac = (r, hash(r, k))`). If the nonce for generating `r` depended only on the transaction number, then it could happen that the user would use the same `r` when resubmitting a transaction, compromising privacy and maybe even security. 

Note that in the above, the choice of nonces is crucial for security. 


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.alephzero.org/aleph-zero/protocol-details/shielder/deterministic-secret-management.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.