Is it possible that there are multiple levels of encryption included in the "S1" algorithm? This question is prompted by reviewing the DoD's Multilevel Security (MLS) Program at: http://www.disa.mil/MLS/mls_home.html One of the features of this program is to design means to simultaneously transmit data with different levels of security, so that communicants send and/or read the data according to their levels of security clearance. This is amplified in Section 3 of the program description at: http://www.disa.mil/MLS/info/basics/sec3.html#2 Excerpts: Multilevel security allows information systems to provide capabilities that augment its existing single-level data processing and data communications services. Data of multiple security levels are processed and transferred by the system, which also separates the different security levels and controls access to the data. ... When a system operates in the multilevel mode, it allows data of two or more security levels to be processed simultaneously when not all users have the clearance, formal authorization, or need to know for all data handled by the system. The system is able to separate and protect the data according to these restrictions. To amplify the definition, an MLS system might process both Secret and Top Secret collateral data and have some users whose maximum clearance is Secret and others whose maximum clearance is Top Secret. Another MLS system might have all its users cleared at the Top Secret level, but have the ability to release information classified as Secret to a network consisting of only Secret users and systems. Still another system might process both Secret and Unclassified information and have some users with no clearance. In each of these instances, the system must implement mechanisms to provide assurance that the system's security policy is strictly enforced. In these examples, the policy allows access to the data by only those users who are appropriately cleared and authorized (e.g., having formal access approval) and who have an official need to know for the data. A related mode of operation is the partitioned mode, also known as compartmented mode. Although similar concepts and solutions are involved for compartmented mode operations as are for the multilevel mode, there is also a key difference. In the compartmented mode, all users have clearances for all the data processed but may not have authorizations for all the data; whereas for multilevel mode, some users may not even be cleared for the highest level. Because the compartmented mode is often envisioned for the intelligence community, all such users would have Top Secret security clearances and often authorizations for one or more, but possibly not all, compartments in the system. End excerpts. There are also descriptions of the soft and hardware implementations of MLS. Would anyone care to comment on how this differentiation of levels of security is done, by a single encryption program or multiples, and if multiples, their arrangement? Is feature then embedded in the hardware, such as the Fortezza card system cited in the program?