I've wiped HDDs using Active Kill Disk and it takes quite some time. I ran Samsung Magician "Secure Erase" on my SSD and it completed almost instantaneously. Is this normal? Do they just change a key that they use to encrypt/store the data? Can the original key be recovered/restored in a way that data can be recovered from a regular HDD?
The data on your drive is always encrypted with AES-256. There is no way to disable it. This means all your data from before try invoked secure erase only makes sense if you can decrypt it.
That key itself is protected by a password. By default no password is assigned and the key is automatically used. This means that the actual data on the flash chips is encrypted and useless for a would be hacker. But the data is decrypted is you read it via the regular SATA interface.
If you throw away this key, e.g. by creating a new one or by invoking secure erase that the data on the disk is still still. But it is still unusable garbage for anyone without the encryption key.
Thus we come to your question:
Yes, secure erase can be very quick. It just has to throw away a key. It probably does some more things like resetting internal tables, but it should finish nigh instantly.
After secure erase all data became zero. Secure erase works by sending a voltage spike to SSD and thus zeroing out all NAND.
According to kingston, secure erase meets law requirement and defeats attacks up to laboratory level so its not recoverable at least to majority of users.
Edit: I've seen several similar questions/answers, all state that SE is done by changing the encryption key which is not the case.
When an ATA Secure Erase (SE) command is issued against a SSD's built-in controller That properly supports it, the SSD controller resets all its storage cells as empty (releasing stored electrons) - just THUS restoring the SSD to factory default settings and write performance. When Implemented properly, SE will process all regions Including the protected storage service regions of the half.
Secure Erase permanently destroys all data stored on the SSD by erasing the data in all cells (by changing them to FF status). In addition, Secure Erase provides a way to reset the SSD to its factory default state if there is a problem with the performance or operation of the SSD.
Secure erase zeros out all NAND cells.