What is cryptographic erase?
Cryptographic erase (CE) is a sanitization method for storage whose contents are encrypted. Instead of erasing every block, it destroys the key that encrypted them. The ciphertext stays on the media, but without the key it cannot be decrypted with any practical effort, so the data is effectively gone. Because only a key is erased, the process takes seconds whatever the drive's capacity, and the media remains usable. NIST SP 800-88 treats cryptographic erase as a purge method. When the same idea is applied to cloud data or databases, it is usually called crypto shredding.
How it works on self-encrypting drives
Inside a self-encrypting drive (SED), the controller encrypts every write with a media encryption key, typically AES-256, that never leaves the drive. The encryption runs whether or not anyone has set a drive password; the password only governs unlocking. A cryptographic erase command tells the drive to discard that key and generate a new one, after which every previously written block reads back as meaningless data.
Drives expose this through standard commands. On an NVMe drive, an admin first confirms support, then runs a sanitize with the crypto erase action:
sudo nvme id-ctrl /dev/nvme0 -H | grep -i 'crypto erase'
sudo nvme sanitize /dev/nvme0 --sanact=4
The sanitize log then reports whether the operation completed. SATA drives offer an equivalent in the ATA sanitize feature set, and TCG Opal drives can be reset with their revert functions.
Software encryption, phones and the cloud
- Software disk encryption: with LUKS on Linux,
cryptsetup luksErasewipes every key slot in the volume header, leaving the volume unreadable. Any header backup, and any escrowed recovery key for BitLocker or FileVault, must be destroyed too, or the data can still be unlocked. - Phones: modern iOS and Android devices encrypt storage by default, so a factory reset that discards the keys works as a cryptographic erase.
- Cloud: deleting a customer-managed key in a key management service makes every volume, bucket or database encrypted under it unreadable. Providers enforce a waiting period before deletion, such as 7 to 30 days in AWS KMS, so plan for it.
Conditions and limits
- Encryption from the start: CE protects only data that was encrypted when written. If software encryption was turned on after data was already stored, older plaintext may survive in spare or remapped blocks on an SSD.
- Every copy of the key: escrowed recovery keys, key backups, exported keys and replicas in a key management service all have to go.
- Trust in the firmware: in 2018, researchers at Radboud University showed that the hardware encryption in several popular SSDs could be bypassed. High-assurance programs therefore verify samples, or follow CE with physical destruction.
- Strength of the cipher: CE is only as strong as the algorithm and key; AES-128 or AES-256 is expected.
Cryptographic erase vs. overwriting and degaussing
Overwriting an SSD from the host is unreliable, because wear leveling may write new data to fresh cells and leave the old ones untouched, and it takes hours on large drives. Degaussing does nothing to flash storage. Cryptographic erase works on SSDs, takes seconds and leaves the drive reusable, which makes it the usual choice for leased equipment, resale and large fleets of encrypted laptops.
Cryptographic erase on the CompTIA Security+ exam
Cryptographic erase belongs to SY0-801 objective 4.2, in the disposal stage of asset management. Wording such as self-encrypting SSDs combined with return to the leasing company, resell or reuse points to cryptographic erase, and sanitize cloud data you cannot physically reach points to destroying the encryption keys. Distractors include degaussing, which does not affect SSDs; multi-pass overwriting, which cannot reach every flash block; formatting; and shredding when the drives must be returned intact.