> 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/universal-call-format.md).

# Universal call format: PrivacyCall / BundleAction

The **shared on-chain payload** exposed by Privacy Core to all applications.

## PrivacyCall

```solidity
struct PrivacyCall {
    bytes actions;           // abi.encode(BundleAction[])
    uint256[3] bindingSig;
}
```

## BundleAction

```solidity
struct BundleAction {
    bytes32    cmx;
    bytes      encCiphertext;    // 580 B
    bytes      outCiphertext;    // 80 B
    bytes32    epk;
    bytes32    nfOld;
    bytes32    anchor;
    bytes      proof;            // Groth16 256 B
    uint256[8] pubFields;
    uint256[3] spendAuthSig;
}
```

## Usage by applications

| Application                    | Call                                                                 |
| ------------------------------ | -------------------------------------------------------------------- |
| pERC20 transfer                | `transfer(PrivacyCall)`                                              |
| pERC20 mint/burn               | `mint` / `burn` + valueBalance                                       |
| Shield ERC20 shield/unshield   | `shield` / `unshield` + valueBalance (+ `recipientMeta` on unshield) |
| pERC20 approve (on-chain step) | `transfer(PrivacyCall)`                                              |

## Calldata size

Single-action `transfer(PrivacyCall)` ≈ **1,900–1,960 B (\~1.9 KB)** when ABI-encoded. Measured from real bundle encoding ([Performance benchmarks](/plabs-docs/ecosystem/performance.md), 2026-06-23).

Groth16 proof is only **256 B raw**, so calldata is **not proof-dominated** — the largest field is **`encCiphertext`** (580 B raw).

### Per-field breakdown (`BundleAction` + `PrivacyCall`)

| Field                                     | Raw   | ABI-encoded | Notes                                                     |
| ----------------------------------------- | ----- | ----------- | --------------------------------------------------------- |
| `cmx`                                     | 32 B  | 32 B        |                                                           |
| `encCiphertext`                           | 580 B | 640 B       | 32 B length word + 580 B + 28 B padding                   |
| `outCiphertext`                           | 80 B  | 128 B       | 32 B length word + 80 B + 16 B padding                    |
| `epk`                                     | 32 B  | 32 B        |                                                           |
| `nfOld`                                   | 32 B  | 32 B        |                                                           |
| `anchor`                                  | 32 B  | 32 B        |                                                           |
| `proof`                                   | 256 B | 288 B       | `abi.encode(pA[2], pB[2][2], pC[2])`; 32 B length + 256 B |
| `pubFields`                               | 256 B | 256 B       | `uint256[8]`                                              |
| `spendAuthSig`                            | 96 B  | 96 B        | `uint256[3]`                                              |
| ABI dynamic offsets + array/tuple headers | —     | \~300 B     | `bytes actions` wrapper + 3 dynamic `bytes` offsets       |
| `bindingSig`                              | 96 B  | 96 B        | `PrivacyCall` layer                                       |
| Function selector                         | —     | 4 B         | `mint` / `burn` add +32 B for `amount`                    |

## Multi-action bundles

Default `maxActions = 10`, cap 16. One `bindingSig` per bundle.

## Encoding reference

* `contracts/interfaces/IEndpointCore.sol`
* `apps/web/src/issuance/bundleCodec.ts`

## Next

→ [Shield ERC20 overview](/plabs-docs/privacy-core/shield-erc20/overview.md)


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