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Encryption and Decryption: Encryption at rest and the addressable analysis

March 20, 2026 · Ken Armstrong

45 CFR 164.312(a)(2)(iv) sets the expectation for encryption and decryption. The text is brief; the evidence it implies is not, and the difference between the two is where most remediation time goes.

What the rule says

Encryption and decryption (Addressable). Implement a mechanism to encrypt and decrypt electronic protected health information.

That is the text of 45 CFR 164.312(a)(2)(iv). Read it closely: it describes an outcome to achieve, not a product to buy, which is why two practices of the same size can satisfy it in different ways and both be right.

This is an addressable implementation specification, and addressable does not mean optional. Under 45 CFR 164.306(d)(3) you assess whether the specification is reasonable and appropriate in your environment, and then either implement it or, if implementing it is not reasonable and appropriate, document why and implement an equivalent alternative measure if that is reasonable and appropriate. The documented reasoning is itself part of the requirement, so an undocumented decision to skip it is the finding.

What this looks like in practice

In an assessment, 45 CFR 164.312(a)(2)(iv) is not one question. It resolves into several, and each one is really asking for different evidence. These are among the questions asked about it:

Has the organization encrypted sensitive data at rest, or, where it has determined encryption is not reasonable and appropriate, documented that determination and implemented an equivalent alternative measure (§164.306(d)(3)), using full-disk or storage-level encryption across servers, workstations, laptops, mobile devices, multi-function printers, backup media, and removable storage?
Does the organization require remote workers who access ePHI to use approved encrypted devices and secure encrypted network connections rather than public or unsecured networks, or, where it has determined that this safeguard is not reasonable and appropriate, documented that determination and implemented an equivalent alternative measure (45 CFR 164.306(d)(3))?
Does the organization manage cryptographic keys across their full life, covering how keys are generated, distributed, stored, rotated, and destroyed, or, where it has determined that this safeguard is not reasonable and appropriate, documented that determination and implemented an equivalent alternative measure (45 CFR 164.306(d)(3))?

Ownership usually sits with the IT or security team, though the evidence is often produced by someone else, which is where the trail breaks. A control that works but has no owner tends to stop working the month the person who quietly maintained it changes roles.

Who this applies to

Every covered entity and every business associate, at any size. 45 CFR 164.306(b) allows flexibility of approach, so a two-provider practice and a hospital system may implement this differently and both comply. What flexibility does not allow is skipping the decision: the smaller the organization, the more the written reasoning carries the weight, because there is no scale of operation to make the control self-evident.

Building it, in order

These steps are one way to meet it, drawn from our question bank. Unless a step names a provision, the Security Rule does not require that particular measure: 45 CFR 164.306(b)(1) lets you use any security measures that allow you to reasonably and appropriately implement the standards and implementation specifications, chosen with the factors in 45 CFR 164.306(b)(2).

The sequence below is the order that produces evidence as a by-product rather than as a separate documentation exercise:

Define a written standard for encryption of data at rest (such as AES-256), identifying which asset classes are in scope and, for any excluded class, recording the risk-based determination that encryption is not reasonable and appropriate plus the equivalent alternative measure implemented instead (45 CFR 164.306(d)(3)).
Inventory every system and medium that stores sensitive data, including servers, laptops, mobile devices, printers, backup media, and USB storage.
Enable full-disk or storage-level encryption on each in-scope asset and verify it is active.
Centrally manage and escrow encryption keys, and monitor for any device that falls out of compliance.
Establish a policy requiring remote access to sensitive data only from organization-approved, encrypted devices. Where the organization determines this safeguard is not reasonable and appropriate, record that determination and the equivalent alternative measure implemented, as 45 CFR 164.306(d)(3) provides.
Require connections through an encrypted tunnel (such as a VPN or equivalent zero-trust access control) and prohibit access over public or unsecured networks unless an equivalent alternative safeguard is documented under 45 CFR 164.306(d)(3).

Where else this maps

The questions behind 45 CFR 164.312(a)(2)(iv) also map to HHS 405(d) HICP (2023 Edition) CSP 2, CSP 4, CSP 6 and NIST SP 800-66 Rev. 2 5.2.4, 5.3.1, 5.3.5, which are voluntary guidance rather than law; following them does not by itself establish compliance with any law. That matters for scoping: the same evidence can be written once and referenced from each, rather than rewritten per framework.

Evidence an assessor asks for

For this requirement the evidence types that satisfy it are configuration, inventory, policy, and procedure. The distinction matters more than it looks: a policy states what you intend to do, a procedure states how, and a record proves it happened on a date. Auditors ask for all three, and a practice that has written the first two often has nothing for the third.

Date every document and keep the superseded versions. 45 CFR 164.316(b)(2)(i) requires the documentation 164.316(b)(1) calls for (the Security Rule policies and procedures, and the written record of any action, activity or assessment the Security Rule requires to be documented) to be retained for six years from the date of its creation or the date when it last was in effect, whichever is later, so a policy you replaced two years ago is still part of the record.

Where this usually goes wrong

The most common failure here is treating addressable as optional. A practice decides the specification does not fit, implements nothing, and writes nothing down. At assessment the answer to "why not" is a verbal explanation, which is not evidence. The second most common failure is the opposite: implementing an alternative that works, and still not recording the reasoning, so the control looks accidental.

What to do about it

Produce the evidence, not the intention. For 45 CFR 164.312(a)(2)(iv) that means a configuration export or screenshot showing the setting live, dated, an inventory with an owner and a last-reviewed date on every row, a signed, dated policy with a named owner and a review date, and a step-by-step procedure someone unfamiliar with the task could follow. If the only evidence is that someone knows how this works, you have a practice and not a record.
Put a name on it. Whoever administers the systems should be recorded as the owner. Where the work is done by someone else, say so in the document: the split between who owns it and who performs it is where the trail usually breaks. A control with no owner stops working the month the person who quietly maintained it changes roles, and nobody notices.
Review it on a fixed date, not when you remember. In our question bank this is weighted Critical: a gap here is raised as a critical finding (a partial answer as high). Put the review on the calendar with an owner, and keep the dated output of each one.
If you decide not to implement it, write the decision down. Addressable is not optional: under 45 CFR 164.306(d)(3) the documented assessment IS part of the requirement, so an undocumented decision to skip it is the finding, and a working alternative with no recorded reasoning looks accidental.

Work backward from the evidence. Decide what evidence would prove encryption and decryption to someone who does not already trust you, then build the control that produces it. Programs built in that order tend to stay current, because the evidence goes stale visibly.

Related requirements

References

45 CFR 164.312(a)(2)(iv), in 45 CFR 164.312 on eCFR. Quoted text verified against the eCFR text current as of 2026-10-06.
The Required and Addressable designations are defined at 45 CFR 164.306(d).
Crosswalk references in this post are the mappings in our question bank, and are not verified against the published text of those standards.
This post describes what a requirement asks for and what evidence documents it. It is not legal advice, and your counsel owns the conclusion. State law may impose additional obligations; HIPAA preempts a State law only where it is contrary to HIPAA (45 CFR 160.202, 160.203).