Load the private key from the file system. The private key is reused once loaded. The library returns a reference to the private key. This can be done by the function fetch_private_key/2. Just read the private key and call the function to receive a reference of the private key. If the private key is encrypted you need to specify the password.

For each request, we do the encryption like this:

1. Decrypt the encrypted AES key
2. Decrypt the request with initial vector and the encrypted AES key
3. Encrypt the response with the inverted initial vector and the encrypted AES key

{:ok, private_key_pem} = File.read(private_pem_path);
WhatsappFlowCrypto.fetch_private_key(private_key_pem, "test")
{:ok, #Reference<0.1652491651.443678740.227250>}copy

After this, you can decrypt the request. The request contains

• the encrypted AES key
• the initial vector
• the encrypted flow data

All values are base64 encoded.

WhatsappFlowCrypto.decrypt_request(private_key_ref, encrypted_aes_key, initial_vector, encrypted_flow_data)
{:ok, {decrypted_body, aes_key, initial_vector}}

WhatsappFlowCrypto.encrypt_response(aes_key, initial_vector, response)
"KUkRnUDAUKqhiovnQ9RRwmdBjcg87/wh+ZrMtbh8xlx3"copy