Move decrypt/encrypt functions to their own modules #4873

Job	Run time
Additional Builds and Concurrency Tests	9m 17s
Basic Checks	6m 12s
miri	4m 17s
Measure coverage	7m 37s
sanitize (address)	6m 37s
Release builds and tests	10m 22s
Slow tests	5m 38s
sanitize (address, multi-threading)	5m 15s
sanitize (leak)	3m 7s
sanitize (leak, multi-threading)	4m 27s
	1h 2m 49s

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