# CompressedPublicKey

33-byte compressed secp256k1 public key with validated prefix byte.

## Definition

```python
class CompressedPublicKey(_SizedHexBytes):
    _size = 33
```

## Construction

| Parameter | Type                  | Required | Description                       |
| --------- | --------------------- | -------- | --------------------------------- |
| `val`     | `bytes \| str \| int` | Yes      | Hex string, raw bytes, or integer |

Raises `ValueError` if:

* Length is not exactly 33 bytes
* First byte is not `0x02` or `0x03`

## Example

```python
from eth_keys import keys as eth_keys
from seismic_web3 import PrivateKey, CompressedPublicKey
import os

private_key = PrivateKey(os.urandom(32))
sk = eth_keys.PrivateKey(bytes(private_key))
pubkey = CompressedPublicKey(sk.public_key.to_compressed_bytes())
```

## Compressed format

Seismic uses compressed public keys exclusively:

* 1-byte prefix (`0x02` for even y, `0x03` for odd y) + 32-byte x-coordinate
* 33 bytes total, versus 65 bytes for uncompressed keys

## See Also

* [PrivateKey](/clients/python/api-reference/types/private-key.md) — corresponding private key type
* [SeismicElements](/clients/python/api-reference/transaction-types/seismic-elements.md) — uses CompressedPublicKey for `encryption_pubkey`
* [ecdh](/clients/python/precompiles/ecdh.md) — ECDH key derivation with public keys


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