The protection tag is totally useless. The SWF format is an open format, otherwise how would you have so many players and tools to work with SWF movies? Thus, you can pretend to protect your movies, but anyone with a simple binary editor can transform the tag and make it another which has no such effect. Also, swf_dump and some other tools (such as flasm) can read your movie anyway.
For the sake of defining what you have in each tag, there are the protection tags fully described.
According to Macromedia, you can find some free implementation of the MD5 algorithm by Poul-Henning Kamp in FreeBSD in the file
src/lib/libcrypt/crypt-md5.c. For your convenience, there is an implementation of that MD5 sum in the SSWF library.
Version 2, 3, 4 must use Protect.
Version 5 must use EnableDebugger.
Version 6 and over must use EnableDebugger2.