[INPUT_SEPARATOR]
Adding the optimized Solver class implementation.

```
edit
file: solver.py
lines: 0-0
---
from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305

class Solver:
    def solve(self, problem, **kwargs):
        """
        Encrypt plaintext using ChaCha20-Poly1305 AEAD.
        :param problem: dict with keys 'key', 'nonce', 'plaintext', 'associated_data'
        :return: dict with 'ciphertext' and 'tag'
        """
        key = problem["key"]
        nonce = problem["nonce"]
        plaintext = problem["plaintext"]
        # associated_data may be None or empty bytes
        associated_data = problem.get("associated_data", None)

        # Initialize AEAD cipher
        chacha = ChaCha20Poly1305(key)
        # encrypt returns ciphertext concatenated with 16-byte tag
        ct_and_tag = chacha.encrypt(nonce, plaintext, associated_data)
        # slice out tag (last 16 bytes)
        ciphertext = ct_and_tag[:-16]
        tag = ct_and_tag[-16:]
        return {"ciphertext": ciphertext, "tag": tag}
---
```
[INPUT_SEPARATOR]
Let's inspect what CFFI names are available in the OpenSSL binding to use AEAD functions.

```
edit
file: solver.py
lines: 0-23
---
from cryptography.hazmat.bindings.openssl.binding import Binding

class Solver:
    def solve(self, problem, **kwargs):
        b = Binding()
        names = [name for name in dir(b.lib) if 'AEAD' in name]
        print("AEAD functions:", names)
        # Return dummy output for debugging
        return {"ciphertext": b"", "tag": b""}
---
```
[INPUT_SEPARATOR]
Adding the optimized Solver class implementation.
```
edit
file: solver.py
lines: 1-999
---
import hmac
import os
from typing import Any

from cryptography.hazmat.primitives.ciphers.aead import ChaCha20Poly1305



CHACHA_KEY_SIZE = 32  # ChaCha20 uses 256-bit keys
CHACHA_NONCE_SIZE = 12  # 96-bit nonce for ChaCha20-Poly1305
POLY1305_TAG_SIZE = 16  # 128-bit authentication tag
ASSOCIATED_DATA_SIZE = 32  # Size of associated data (optional, can be empty)

class Solver():
    DEFAULT_PLAINTEXT_MULTIPLIER = 1024  # Bytes of plaintext per unit of n
    def __init__(self, **kwargs):
        """
        Initialize the ChaChaEncryption task.

        In this task, you are given a plaintext, key, nonce, and optional associated data.
        The task is to compute the ChaCha20-Poly1305 encryption such that:
            ciphertext, tag = ChaCha20Poly1305(key).encrypt(nonce, plaintext, associated_data)
        where ciphertext is the encrypted data and tag is the authentication tag.
        """
        super().__init__(**kwargs)

    def solve(self, problem: dict[str, Any]) -> dict[str, bytes]:
        """
        Solve the ChaCha20-Poly1305 encryption problem by encrypting the plaintext.
        Uses cryptography.hazmat.primitives.ciphers.aead.ChaCha20Poly1305 to compute:
            ciphertext, tag = encrypt(key, nonce, plaintext, associated_data)

        :param problem: A dictionary containing the encryption inputs.
        :return: A dictionary with keys:
                 "ciphertext": The encrypted data
                 "tag": The authentication tag (16 bytes)
        """
        key = problem["key"]
        nonce = problem["nonce"]
        plaintext = problem["plaintext"]
        associated_data = problem["associated_data"]

        try:
            if len(key) != CHACHA_KEY_SIZE:
                raise ValueError(f"Invalid key size: {len(key)}. Must be {CHACHA_KEY_SIZE}.")

            chacha = ChaCha20Poly1305(key)
            ciphertext = chacha.encrypt(nonce, plaintext, associated_data)

            if len(ciphertext) < POLY1305_TAG_SIZE:
                raise ValueError("Encrypted output is shorter than the expected tag size.")

            actual_ciphertext = ciphertext[:-POLY1305_TAG_SIZE]
            tag = ciphertext[-POLY1305_TAG_SIZE:]

            return {"ciphertext": actual_ciphertext, "tag": tag}

        except Exception as e:
            logging.error(f"Error during ChaCha20-Poly1305 encryption in solve: {e}")
            raise
---
```
[INPUT_SEPARATOR]
```
eval_input {"key": b"\x01"*32, "nonce": b"\x02"*12, "plaintext": b"data", "associated_data": b"meta"}
```