# Precompiles

Seismic adds six precompiled contracts to the EVM, giving smart contracts access to cryptographic primitives that would be prohibitively expensive to implement in Solidity. All standard Ethereum precompiles (e.g. `ecrecover`, `sha256`) remain available at their usual addresses.

Precompiles are called like regular contracts using `staticcall` or `call` to their fixed addresses. They execute native code rather than EVM bytecode, making them significantly cheaper and faster than equivalent Solidity implementations.

{% hint style="warning" %}
All precompiles expect **raw concatenated bytes** as input, not ABI-encoded data. Use `abi.encodePacked` (not `abi.encode`) when constructing input in Solidity.
{% endhint %}

These are the precompiles Seismic adds:

| Name            | Address                                                                      | Purpose                                                |
| --------------- | ---------------------------------------------------------------------------- | ------------------------------------------------------ |
| RNG             | [`0x64`](https://docs.seismic.systems/reference/precompiles/rng)             | Securely generate random bytes inside the TEE          |
| ECDH            | [`0x65`](https://docs.seismic.systems/reference/precompiles/ecdh)            | Derive an AES key from a private key and a public key  |
| AES-GCM Encrypt | [`0x66`](https://docs.seismic.systems/reference/precompiles/aes-gcm-encrypt) | Encrypt data with AES-256-GCM authenticated encryption |
| AES-GCM Decrypt | [`0x67`](https://docs.seismic.systems/reference/precompiles/aes-gcm-decrypt) | Decrypt data with AES-256-GCM authenticated encryption |
| HKDF            | [`0x68`](https://docs.seismic.systems/reference/precompiles/hkdf)            | Derive a 32-byte key from input key material           |
| secp256k1 Sign  | [`0x69`](https://docs.seismic.systems/reference/precompiles/secp256k1-sign)  | Sign a message hash with a secp256k1 private key       |

## Common pattern: Encrypted events

A frequent use of the precompiles is encrypting event data so that only the intended recipient can read it. The typical flow chains ECDH and AES-GCM Encrypt together:

```solidity
// 1. Derive an AES key via ECDH
sbytes32 aesKey = sbytes32(ecdh(contractPrivKey, recipientCompressedPubKey));

// 2. Generate a random nonce
uint96 nonce = uint96(unsafe_rng_u96());

// 3. Encrypt the sensitive data
bytes memory encrypted = aes_gcm_encrypt(aesKey, nonce, plaintext);

// 4. Emit a regular event with the encrypted bytes
emit EncryptedData(msg.sender, recipient, nonce, encrypted);
```

For a complete walkthrough of this pattern, see [Events](https://docs.seismic.systems/seismic-solidity/events).