how to backup files from an encrypted SD card for upgrade recently bought a new SD card and I want to transfer the files from my current one to the new card.
However, the files on the current card are encrypted and I have no way to copy them.
I need some way I can either force the phone to allow my desktop PC to recognize the encryption algorithm and decrypt the data on the fly so that Windows will read them correctly, or I need to decrypt the card.
I'm upgrading from a 2 gigabyte card to an 8gb one.
I would simply transfer the files to the phone's internal memory, but the card is too big. The phone only has 2gb internal storage and half of it is being used by the operating system.

I have a Samsung SCH- i110 Illusion on Verizon. 
Android 2.36 gingerbread
The PIN/password is not the key used to encrypt/decrypt. The PIN/password is used to decrypt the key used to encrypt/decrypt (that's why one can change the PIN/password without re-encrypting the whole disk). Android does not provide a way to backup the encryption keys. 

So the easiest things to do is insert the old SD card to the phone, and via Wifi copy the files to the desktop PC. Then insert the new SD card, and copy the files from the desktop PC back to the phone.

For this you can use apps like AndFTP on the phone and FileZilla Server on Windows or openssh-server on Linux.