In today’s defense industrial base (DIB), cybersecurity is no longer optional—it is a contractual requirement. Department of Defense (DoD) contractors and subcontractors handling Controlled Unclassified Information (CUI) must implement strong encryption mechanisms to meet CMMC Level 2 requirements. At the core of modern encryption strategies are public keys and private keys, which power secure email, file sharing, authentication, and digital signatures.
At CMMC IT Support, we help San Diego–based and nationwide DoD contractors design, implement, and validate encryption solutions that align with CMMC, NIST SP 800‑171, and DFARS 252.204‑7012. This guide explains how public key encryption and private key encryption work, why they matter for compliance, and how your organization can avoid common audit failures.
If you’re unsure whether your encryption approach will pass a CMMC assessment, we encourage you to schedule a free compliance call, call us at 858‑483‑8770, or email info@cmmcitsupport.us.
Public Keys and Private Keys: The Foundation of Modern Encryption
Public key cryptography—also known as asymmetric encryption—relies on a mathematically linked pair of keys:
- A public key, which can be shared openly
- A private key, which must be kept secret by its owner
Together, these keys enable secure communication even over untrusted networks like the internet. Unlike older symmetric encryption models, public key systems eliminate the need to securely exchange a shared secret before communication begins.
From a CMMC perspective, this model is critical because it supports:
- Encryption of CUI in transit
- Strong identity verification
- Secure authentication and access control
- Digital signatures for integrity and non‑repudiation
Public Keys vs Private Keys: How They Work Together
Understanding public keys vs private keys is essential for both technical teams and compliance leaders.
A message encrypted with a public key can only be decrypted with the corresponding private key. This ensures confidentiality, even if attackers intercept the data.
A useful analogy:
- A public key is like a company’s mailing address—anyone can use it to send you something
- A private key is like the key to your mailbox—only you can open it
In compliant systems, private keys are never shared, never transmitted in plaintext, and are often protected using hardware security modules (HSMs), secure enclaves, or FIPS‑validated cryptographic modules.
How Public Key Encryption Supports CMMC Requirements
Public key encryption is explicitly and implicitly referenced throughout NIST SP 800‑171, which underpins CMMC Level 2. Controls related to cryptographic protection (3.13.8), identification and authentication (3.5.x), and system communications protection rely on asymmetric cryptography.
When implemented correctly, public key systems help organizations:
- Encrypt emails containing CUI
- Secure file transfers and collaboration portals
- Protect VPN and TLS communications
- Enable strong MFA and certificate‑based authentication
At CMMC IT Support, we frequently identify gaps where organizations believe they are “encrypted,” but are actually failing to properly manage keys—an issue that can lead to assessment failure.
Private Key Encryption and Why Key Protection Matters
While public keys are designed to be shared, private key encryption depends entirely on secrecy. If a private key is compromised, attackers can decrypt sensitive data or impersonate legitimate users.
Common private key risks we see during CMMC readiness assessments include:
- Keys stored unencrypted on endpoints
- Shared administrator accounts using the same private keys
- Lack of key rotation policies
- No documented key revocation procedures
CMMC assessors increasingly scrutinize how private keys are generated, stored, rotated, and revoked. Proper key management is just as important as the encryption algorithm itself.
Public and Private Key Example in a CMMC Context
Consider a DoD subcontractor sending CUI via encrypted email:
- The sender encrypts the email using the recipient’s public key
- The encrypted message travels securely across the internet
- Only the recipient can decrypt the message using their private key
Even if an attacker compromises the email server, the data remains unreadable without the private key. This model directly supports confidentiality requirements under CMMC Level 2.
When replying, the process repeats using the sender’s public key—ensuring secure, bidirectional communication.
Algorithms Commonly Used for Public and Private Keys
Several well‑established algorithms generate asymmetric key pairs. The most common include:
- RSA (Rivest‑Shamir‑Adelman): Widely used, though larger key sizes are required for modern security
- Elliptic Curve Cryptography (ECC): More efficient and increasingly preferred for CMMC‑aligned systems
- DSA/DSS: Used primarily for digital signatures in federal systems
For compliance, algorithms must be implemented using FIPS 140‑2 or 140‑3 validated cryptographic modules, a requirement many organizations overlook until assessment time.
Digital Signatures, Authentication, and Trust
Beyond encryption, public‑private key systems enable digital signatures, which verify:
- The sender’s identity
- Message integrity
- Non‑repudiation
A digital signature is created using the sender’s private key and verified using their public key. This prevents impersonation attacks and supports CMMC controls related to authentication and integrity.
Without digital signatures, organizations remain vulnerable to man‑in‑the‑middle attacks—an issue assessors increasingly flag.
Benefits of Public and Private Keys for CMMC Compliance
When implemented correctly, asymmetric cryptography delivers three core security assurances:
- Confidentiality: Only authorized recipients can access CUI
- Integrity: Data cannot be altered without detection
- Authenticity: Users are verified beyond passwords alone
These principles align directly with DoD expectations and are foundational to passing a CMMC Level 2 assessment.
Common CMMC Encryption Mistakes We See
Even organizations using modern tools often fail CMMC assessments due to:
- Misconfigured email encryption
- Inadequate key management documentation
- Use of non‑FIPS‑validated encryption
- Overreliance on vendor claims without evidence
CMMC assessors require proof—not assumptions. Policies, procedures, diagrams, and screenshots must clearly demonstrate how encryption and key management are implemented.
How CMMC IT Support Helps You Get Encryption Right
As a San Diego‑based consultancy, CMMC IT Support specializes in helping DoD contractors operationalize encryption—not just talk about it.
We assist with:
- Encryption architecture design
- Public and private key management strategies
- Secure email and file collaboration solutions
- Policy and procedure development
- Evidence preparation for CMMC assessments
Whether you’re preparing for your first assessment or remediating gaps, our team ensures your encryption strategy aligns with real assessor expectations.
Take the Next Step Toward CMMC Compliance
If you’re unsure whether your current use of public keys and private keys meets CMMC Level 2 requirements, don’t wait until assessment day to find out.
👉 Schedule a free compliance call today
📞 Call 858‑483‑8770
📧 Email info@cmmcitsupport.us
At CMMC IT Support, we don’t just explain encryption—we help you prove compliance.
