My S5's screen died about a week ago and as a result the phone will be getting swapped. It has some pretty sensitive information on it (such as numbers, credit card info, photos, etc.) that I want to get rid of:permanently. Lately I've been overwriting the internal memory using "dd if=/dev/urandom of=/sdcard/junkfile" in ADB and was wondering if this would be enough to make sure my data is gone for good. I've also wiped it about 5 times.
You've done great so far. Now, write junk files again and encrypt the device over ADB Shell:
/system/bin/vdc cryptfs enablecrypto inplace PASSWORD
(Your device may need to be rooted for this)
Now, feel free to wipe.