help with encryptor - please?!?!

[IE63@vaxb.acs.unt.edu]

     I've been working on a program for MS-DOS machines that will
encrypt and/or password protect .COM and .EXE files.  The way it works
is this: It encrypts the entire file specified by the user, then it
uses a polymorphic encryptor to encrypt the decryption code for the file 
and put it in a decryption envelope filled with anti-debugging code.  IT
then attaches the entire module/decryption code to the file so that it 
is executed initially when the file is run - at which point it decrypts
the file and does whatever relocation is needed (for .EXE files).  In
the case of a password - it asks for the password, encrypts it and checks
it against the stored version, then if they match it decrypts restoration
code using the password as a key and continues on.  

    I've got it working really well at this point - but my encryption 
algorithms are rather simple.  I'm fairly new in the encryption biz, 
and I was wondering what would be good to use for the file encryption 
algorithm to make it as secure as possible?  Of course - the code to 
decrypt it MUST be present in the file, so if you can bypass the anti-
debugging code it's yours, but the polymorphism makes it difficult to 
do this on more than a case-by-case basis.  Still - I'd like to make
it to where one can't just run a "decrypt-em-all" analysis program on it
and be able to read the included text - but I need a good algorithm 
for it.  Any help/suggestions would REALLY be appreciated.  Oh -
if you are interested in the protection utilities, email me at the
address below - it's freeware.

Thanks a lot,
Michael Ellison
ie63@vaxb.acs.unt.edu

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