> For the complete documentation index, see [llms.txt](https://plabs.gitbook.io/plabs-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://plabs.gitbook.io/plabs-docs/privacy-core/shield-erc20/interface-and-perc20.md).

# Interface & pERC20 mapping

`ERC20Shield` implements `IERC20Shield`, which extends `IPERC20`. Wallets and SDKs reuse the same `PrivacyCall` / `BundleAction` encoding as [pERC20](/plabs-docs/privacy-core/perc20/interface-and-erc20.md).

## Full mapping

| Interface                     | pERC20                     | Shield ERC20                                                       |
| ----------------------------- | -------------------------- | ------------------------------------------------------------------ |
| `name/symbol/decimals`        | On-chain, public           | Same (pool metadata; independent of underlying)                    |
| `totalSupply()`               | `mint − burn` (note units) | `shieldedSupply` (note units)                                      |
| `issuer()`                    | Token issuer               | **`admin`** (compliance officer; no mint power)                    |
| `underlying()`                | —                          | Custodied ERC-20 address                                           |
| `scale()`                     | —                          | Wei per note unit                                                  |
| `shieldedSupply()`            | —                          | Backed note units (alias of `totalSupply`)                         |
| `balanceOf(addr)`             | Off-chain viewing key      | Same                                                               |
| `transfer(PrivacyCall)`       | Private note→note          | Same                                                               |
| `transfer(executor, call)`    | Executor-gated (swap)      | Same                                                               |
| `mint(...)`                   | Issuer only                | **Disabled** — use `shield`                                        |
| `burn(...)`                   | Any holder                 | **Disabled** — use `unshield`                                      |
| `shield(...)`                 | —                          | Deposit underlying → shielded note                                 |
| `unshield(...)`               | —                          | Spend note → release underlying                                    |
| `cmxFrozenRoot/setFrozenRoot` | Admin                      | Same — [Compliance](/plabs-docs/privacy-core/compliance-freeze.md) |

## Events

| pERC20                        | Shield ERC20                                    |
| ----------------------------- | ----------------------------------------------- |
| `Perc20Created`               | `ShieldPoolCreated` (+ `underlying`, `scale`)   |
| `Mint` / `Burn`               | ❌ not emitted (mint/burn disabled)              |
| —                             | `Shielded(depositor, amountUnits, weiAmount)`   |
| —                             | `Unshielded(recipient, amountUnits, weiAmount)` |
| `NoteAdded` / `NoteConfirmed` | Same (all value changes)                        |
| `FrozenRootUpdated`           | Same                                            |

Shield/unshield emit **public amounts** (note units + wei); depositor/recipient identity for shield is not indexed on-chain beyond `msg.sender` on `Shielded`.

## IPERC20 compatibility notes

* **`mint` / `burn` revert** with `MintDisabled` / `BurnDisabled`. Integrators must route deposit/withdraw through `shield` / `unshield`.
* **`issuer()`** returns `admin`, not a mint authority. For shield pools, treat `admin` as the compliance officer only.
* **Asset identity is the shield pool address**, not `(underlying, name)`. Permissionless factory deployment means look-alike pools are possible — verify `ERC20ShieldFactory.isShieldPool(pool)` before interacting.

## ERC-20 layer (public)

| Step     | On-chain (public)                                               | Private                  |
| -------- | --------------------------------------------------------------- | ------------------------ |
| Shield   | `approve(pool, amountUnits * scale)` then `shield` pulls ERC-20 | Output note recipient    |
| Unshield | `unshield(..., recipient, call)` sends ERC-20 to `recipient`    | Spent notes, change note |
| Transfer | —                                                               | Parties and amount       |

Only **standard ERC-20** tokens are supported. Fee-on-transfer and rebasing tokens are rejected at `shield` via balance-delta check (`NonStandardToken`).

## Relation to Privacy Core

All note state transitions go through `_executeBundle` on `OrchardVerifier`. `ERC20Shield` adds custody accounting (`shieldedSupply`) and ERC-20 pull/transfer around shield/unshield.

## Next

* [Operations](/plabs-docs/privacy-core/shield-erc20/operations.md)
* [Deployment](/plabs-docs/privacy-core/shield-erc20/deployment.md)


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