When building a large and complex system using the microservices architecture with multiple client apps, a good approach to consider is API Gateway Pattern.
The following illustration explains how an HTTP POST request can be configured for multiple files in a single request using RAML 1.0 and Mule version 4.1.4.
See how to encrypt and decrypt stream, byte[], or string using the Asymmetric JCE Cryptography module in Mule 4 taking an API as the reference implementation.