{
    "bsonType": "object",
    "properties": {
        "encrypted_string": {
            "encrypt": {
                "keyId": [
                    {
                        "$binary": {
                            "base64": "LOCALAAAAAAAAAAAAAAAAA==", 
                            "subType": "04"
                        }
                    }
                ], 
                "bsonType": "string", 
                "algorithm": "AEAD_AES_256_CBC_HMAC_SHA_512-Deterministic"
            }
        }
    }
}