I want to directly convert it to .ply to import both the modeling information and texture information of the dcm file exported from 3shape, but I know that if there is no decryption key, I have to use brute force.
Sorry, I find it very hard to understand what you would like to do. What outputs you can export from 3shape, in which file format? Can you provide an example file? (upload it somewhere and post the link here)
I’m not sure if there is a way to store textured surface mesh in standard DICOM information object. Even if there is, 3shape probably uses private fields instead, as it allows them to lock people into using their software and charge extra for various data export features.
If they don’t offer textures surface mesh export (or it is not affordable) then you can reverse-engineer the contents of the private fields. However, they can change the private fields at anytime and they can make it very hard to decipher the private field contents if they want to.
Overall, probably your best options are either
A. pay for the appropriate data export features in 3shape, or