| key | JWK | **Required.** A [JSON Web Key](https://tools.ietf.org/html/rfc7517#appendix-A.3) object. |
| iv | string | **Required.** The 128-bit unique counter block used by AES-CTR, encoded as unpadded base64. |
| hashes | {string: string} | **Required.** A map from an algorithm name to a hash of the ciphertext, encoded as unpadded base64. Clients should support the SHA-256 hash, which uses the key `sha256`. |
| v | string | **Required.** Version of the encrypted attachments protocol. Must be `v2`. |
| v | string | **Required.** Version of the encrypted attachment's protocol. Must be `v2`. |