1. A method for providing a single level secure user processor with multi-level secure file services, comprising: communicating a request for a classified executable file from said single level secure user processor to a multi-level secure (MLS) service module over a physically-secure data communication path; responsive to said request, accessing with a cryptographic processor of said MLS service module an MLS file system containing said classified executable file which is in an encrypted form; decrypting said classified executable file with said cryptographic processor; verifying, at said cryptographic processor, an integrity of said decrypted classified executable file; in response to said verification of said integrity of said decrypted classified executable file, selectively enabling with said MLS service module a write function for program memory of said single level secure user processor; communicating said decrypted classified executable file from said MLS service module to said single level secure user processor over said physically-secure data communication path; and disabling with said MLS service module said write function immediately after said decrypted classified executable file has been loaded into said program memory of said single level secure user processor.