NIST SP 800-88 Rev 2 3.2.2: Applicability of CE: only where no sensitive plaintext was ever stored since the last sanitization, with caution for long-lived sensitivity, and never trusted where keys were backed up or escrowed without control

What does 3.2.2 require?

CE can only sanitize keys tied to encrypted data, so as a precondition no sensitive data may previously have been stored on the ISM in plaintext (counted since the last proper sanitization); plaintext requires another technique, though virtual storage may offer no purge alternative. Self-encrypting drives, whose encryption is always on, usually include sanitization capability. Sensitivity matters: for information whose confidentiality must last decades, the ciphertext remains on the medium and future cryptographic weaknesses or computational advances could expose it, so CE may not be acceptable. CE is not trusted on ISM whose data, credentials or keys were ever backed up or placed in escrow, except where the organisation is highly confident about in how and where those keys were stored and managed outside the ISM; such copies fall under a separate sanitization policy.