Android - slow decryption for encrypted text

[VM02 0]

With my old and slow android phone, I decrypted a short paragraph. It takes maybe 45 seconds to a minute before the plaintext shows up.

Is this a bug? Or is the decryption process so intensive that my old phone's CPU takes a while to decypt it?

Probably need to need to place an animated hourglass  or something so people won't assume that it doesnt work