ExWapp.Media.Crypto (ExWapp v0.1.2)

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WhatsApp media encryption and decryption helpers.

This follows the same media-key expansion used by popular WhatsApp Web clients: HKDF-SHA256 expands the 32-byte media key into IV, cipher, MAC, and reference keys. The payload is then encrypted with AES-256-CBC and protected with the first 10 bytes of an HMAC-SHA256 digest over IV || ciphertext.

Summary

Types

media_keys()

Functions

decrypt_download(body, ref)

Decrypts an encrypted media body, or accepts a server-declared unencrypted body when no encrypted SHA-256 is present, and validates all available integrity checks.

derive_keys(media_key, type)

Derives WhatsApp media keys for the given media type.

encrypt_upload(plaintext, type)

Encrypts plaintext media bytes and returns upload metadata plus encrypted body.

media_info(atom)

Returns the WhatsApp HKDF context string for a media type.

Types

media_keys()

@type media_keys() :: %{
  iv: binary(),
  cipher_key: binary(),
  mac_key: binary(),
  ref_key: binary()
}

Functions

decrypt_download(body, ref)

@spec decrypt_download(binary(), ExWapp.Media.Ref.t()) ::
  {:ok, binary()} | {:error, term()}

Decrypts an encrypted media body, or accepts a server-declared unencrypted body when no encrypted SHA-256 is present, and validates all available integrity checks.

derive_keys(media_key, type)

@spec derive_keys(binary(), ExWapp.Media.media_type()) :: media_keys()

Derives WhatsApp media keys for the given media type.

encrypt_upload(plaintext, type)

@spec encrypt_upload(binary(), ExWapp.Media.media_type()) ::
  {:ok, ExWapp.Media.Upload.t(), binary()}

Encrypts plaintext media bytes and returns upload metadata plus encrypted body.

media_info(atom)

@spec media_info(ExWapp.Media.media_type()) :: binary()

Returns the WhatsApp HKDF context string for a media type.