The Critical Role of Correct Versioning in P2PE Applications: Why Wildcards Matter

In the world of payment security, Point-to-Point Encryption (P2PE) stands as one of the most stringent standards for protecting cardholder data. For software vendors, merchants, and solution providers working in this space, compliance isn’t optional, it’s mandatory. That compliance extends far beyond code quality or encryption strength. It stretches into how versions of software are managed, tracked, and submitted for validation.

One overlooked—but absolutely critical—aspect of this is versioning methodology, particularly the correct usage of wildcards in application versioning. At first glance, versioning might seem like a clerical detail. But in the P2PE ecosystem, incorrect wildcards can lead to failed audits, invalidated listings, and costly delays in the compliance pipeline.

Let’s break down why getting versioning right is non-negotiable, and why your wildcards need to exactly match the structure of your application versioning format.

Why Versioning Even Matters in P2PE

P2PE is about control, traceability, and verifiability. Every component of a P2PE solution—from the hardware device to the key management system to the software application—must be tightly controlled, and versioning is a core part of that.

Version numbers aren’t just labels. They tell QSA (Qualified Security Assessor) auditors exactly which version of your application has been tested, validated, and included in the listed P2PE solution. If a merchant installs a different version—even a minor patch that wasn’t covered by the validation—it can potentially bring the entire solution out of scope.

This is where wildcards come in. Wildcards are used during the application submission process to define a range of application versions that share the same security-relevant codebase. But to ensure clarity and enforce limits, wildcards must follow strict patterns that reflect the actual versioning scheme.

And that’s where many developers—and even some compliance teams—get it wrong.

The Wildcard Rule: It's Not Just Syntax

Let’s say your application is versioned as 3.0.1.25. If you're submitting this to a P2PE listing and you want to allow for future patching flexibility, you might be tempted to use a wildcard like 10.0.1.x.

That’s incorrect.

Your wildcard pattern must match the character structure of your actual version. Therefore, if your application version has four parts (e.g., major.minor.patch.build), your wildcard must also have four parts, with the wildcard placeholder (e.g., x or xx) reflecting the full character length of what it replaces.

For example:

The placement and length of each segment must remain consistent. This isn’t about style or aesthetics. It’s about precision and control. Wildcards that don’t match the version structure create ambiguity—and ambiguity is the enemy of security validation.

Technical FAQ for versioning separators

Regarding P2PE Application versioning, the below are the acceptable “separators” used between alphanumeric elements as denoted in the P2PE Program Guide, Appendix E:

Use of any other characters (e.g., spaces, commas, etc.) is not permitted.

Technical FAQ for Using the Correct Wildcards

A “wildcard” element is a variable character that may be substituted for a defined subset of possible characters in an application versioning scheme.

The following information is in addition to the information in the PCI P2PE Program Guide, Appendix E: 

• Reminder that wildcards can ONLY be used at the rightmost portion of the version number, and there cannot be a non-wildcard to the right of any wildcard. 
• A wildcard is a single character variable that can be a lowercase {‘x’, ‘y’, ‘z’}, an uppercase {‘X’, ‘Y’, ‘Z’}, or an asterisk ‘*’. Therefore, any other alphabetic characters cannot be a wildcard character. 

E.g., this is NOT allowed: 12.x.36, or 1.ABx.2. 

• The allowable wildcard characters above cannot be used as non-wildcard characters. 
• More than one wildcard is allowed, and it can be a mix of allowable wildcards. 

E.g., ‘9.12*x’, or ‘1-xyz’, or ‘55.x.**’ 

• Allowable ‘separators’ are allowed between wildcards. 

E.g., 1.x-yz 

• A single wildcard can be used to represent a single digit replacement {0-9}.  
• Therefore, ‘x’ = {0-9}, ‘xx’ = {00-99}, ‘x.y’ = {0-9.0-9}, etc. 

E.g., this is allowed: ‘1.xx’ = ‘1.02’ 

E.g., this is NOT allowed: ‘1.x’ = ‘1.201’, or ‘1.x’ = ‘1.A’. 

• A wildcard cannot represent another wildcard, cannot be substituted with an alphabetic character, and cannot be replaced with any non-single digit number. 

E.g., the following is NOT allowed: 34.12.x = 34.12.{a-z or A-Z}.

Why Incorrect Wildcards Cause Real Problems

An incorrect wildcard isn’t just a clerical error. It can have cascading effects:

1. Invalid P2PE Listing

If your wildcard doesn’t correctly match your version structure, the listing may be rejected outright by the QSA or the PCI SSC. This can delay go-to-market timelines and force a resubmission.

2. Unintended Version Coverage

A too-broad wildcard (e.g., using x instead of xx or xxx) could inadvertently imply coverage of versions you never tested or validated. That’s a major liability, especially if a future patch introduces a vulnerability.

3. Audit Trail Breakage

Auditors rely on version numbers to establish a secure lineage. Inconsistent wildcarding compromises that audit trail and makes it harder to prove compliance over time.

4. False Assumptions by Integration Partners

A downstream partner might assume that all 10.3.x.xx versions are covered when, in fact, the submitted wildcard 10.3.xx.xx doesn’t match their deployed version. That can leave merchants exposed.

Versioning Best Practices for P2PE Applications

To avoid these pitfalls, software vendors and P2PE solution providers should adopt and enforce a strict versioning discipline. Here’s how.

1. Define a Fixed Versioning Schema

Stick to a consistent version format (e.g., major.minor.patch.build) and document what each field means. Don’t vary the structure across releases.

Example: 10.3.1.25

• 10: Major architecture or encryption change
• 3: Feature set
• 1: Patch
• 25: Internal build number

2. Use Wildcards Precisely

If your version is 10.3.1.25, then acceptable wildcards might be:

• 10.3.1.xx (covers all build numbers under patch 1)
• 10.3.x.xx (covers all patch+build under minor 3)
• But not 10.3.x.x or 10.3.xx.xx

Each wildcard segment must mirror the format of what it replaces.

3. Align Code Releases with Wildcard Submissions

If you plan to use a wildcard like 10.3.1.xx, make sure all versions you release under that umbrella match in security architecture. Otherwise, you’ll invalidate your listing and risk noncompliance.

4. Coordinate with Your QSA Early

Don’t guess. Work closely with your QSA during the submission process. Show them your versioning plan and get sign-off on your wildcard structure before it goes to PCI SSC.

5. Avoid Over-Wildcarding

Don’t wildcard more than necessary. The more flexible your wildcard, the more tightly you must control what versions fall under it. Only wildcard as far as you're confident you can guarantee full codebase consistency.

Real-World Example: What Happens When It Goes Wrong

Imagine a scenario where a vendor releases a P2PE application versioned 10.3.1.5 and submits it with a wildcard 10.3.x.x. Months later, they release a new version 10.3.4.77 with significant backend changes—but forget to update the listing.

Because 10.3.x.x was used, that version is technically "covered." But in reality, it’s not the same security codebase. When an incident occurs and an audit is triggered, the mismatch between the actual application and the validated version becomes clear.

Result? The solution is pulled from the listing. The merchant’s deployment is retroactively declared non-compliant. Legal and financial fallout follows.

All because of a non-compliant wildcard.

Making It Easy: A Simple Wildcard Checklist

Before submitting a wildcarded version to PCI:

• Does your version structure always follow the same number of segments?
• Does your wildcard match that structure, character for character?
• Is each x or xx an accurate replacement for the digits it covers?
• Have all versions within the wildcard been tested to ensure they share the same security-relevant code?
• Has your QSA reviewed and approved your wildcard use?

If any of these are a "no," fix it before submission.

Final Thoughts: Details Matter

In P2PE, details aren’t optional, they’re the foundation. Every part of the process is about control, repeatability, and trust. Your versioning system is a security control. Your wildcarding is part of your application’s compliance boundary. You can’t afford to be vague or disorganized.

Getting versioning right isn’t about pedantic formatting. It’s about building secure systems that pass audit, protect cardholder data, and keep merchants in the safe zone.

So, the next time you write 10.3.1.25, think carefully about your wildcard. Is it 10.3.1.xx or 10.3.1.x? That one missing x might be the difference between compliance and chaos.

TL;DR: Use wildcards that exactly match your versioning structure. No shortcuts. No assumptions. Just precision.