Public Key Infrastructure (PKI)


What is Public Key Infrastructure (PKI)?

The Public key infrastructure (PKI) is the set of hardware, software, policies, processes, and procedures required to create, manage, distribute, use, store, and revoke digital certificates and public-keys. The PKI is the foundation that enables the use of technologies, such as digital signatures and encryption, across large user populations. PKIs deliver the elements essential for a secure and trusted business environment for e-commerce and the growing Internet of Things (IoT).
PKIs help establish the identity of people, devices, and services – enabling controlled access to systems and resources, protection of data, and accountability in transactions. Next generation business applications are becoming more reliant on public key infrastructure (PKI) technology to guarantee high assurance as evolving business models are becoming more dependent on electronic interaction requiring online authentication and compliance with stricter data security regulations.


The Role of Certificate Authorities (CAs)

In order to bind public keys with their associated user (owner of the private key), PKIs use digital certificates. Digital certificates are the credentials that facilitate the verification of identities between users in a transaction. Much as a passport certifies one’s identity as a citizen of a country, the digital certificate establishes the identity of users within the ecosystem. Because digital certificates are used to identify the users to whom encrypted data is sent, or to verify the identity of the signer of information, protecting the authenticity and integrity of the certificate is imperative to maintain the trustworthiness of the system.
Certificate authorities (CAs) issue the digital credentials used to certify the identity of users. CAs underpin the security of a PKI and the services they support, and therefore can be the focus of sophisticated targeted attacks. In order to mitigate the risk of attacks against CAs, physical and logical controls as well as hardening mechanisms, such as hardware security modules (HSMs) have become necessary to ensure the integrity of a PKI.


PKI Deployment

PKIs provide a framework that enables cryptographic data security technologies such as digital certificates and signatures to be effectively deployed on a mass scale. PKIs support identity management services within and across networks and underpin online authentication inherent in secure socket layer (SSL) and transport layer security (TLS) for protecting internet traffic, as well as document and transaction signing, application code signing, and time-stamping. PKIs support solutions for desktop login, citizen identification, mass transit, mobile banking, and are critically important for device credentialing in the IoT. Device credentialing is becoming increasingly important to impart identities to growing numbers of cloud-based and internet-connected devices that run the gamut from smart phones to medical equipment.


Cryptographic Security

Using the principles of asymmetric and symmetric cryptography, PKIs facilitate the establishment of a secure exchange of data between users and devices – ensuring authenticity, confidentiality, and integrity of transactions. Users (also known as “Subscribers” in PKI parlance) can be individual end users, web servers, embedded systems, connected devices, or programs/applications that are executing business processes. Asymmetric cryptography provides the users, devices or services within an ecosystem with a key pair composed of a public and a private key component. A public key is available to anyone in the group for encryption or for verification of a digital signature. The private key on the other hand, must be kept secret and is only used by the entity to which it belongs, typically for tasks such as decryption or for the creation of digital signatures.


The Increasing Importance of PKIs

With evolving business models becoming more dependent on electronic transactions and digital documents, and with more Internet-aware devices connected to corporate networks, the role of a public key infrastructure is no longer limited to isolated systems such as secure email, smart cards for physical access or encrypted web traffic. PKIs today are expected to support larger numbers of applications, users and devices across complex ecosystems. And with stricter government and industry data security regulations, mainstream operating systems and business applications are becoming more reliant than ever on an organizational PKI to guarantee trust.
What is certification authority or root private key theft?

The theft of certification authority (CA) or root private keys enables an attacker to take over an organization’s public key infrastructure (PKI) and issue bogus certificates, as was done in the Stuxnet attack. Any such compromise may force revocation and reissuance of some or all of the previously issued certificates. A root compromise, such as a stolen root private key, destroys the trust of your PKI and can easily drive you to reestablish a new root and subsidiary issuing CA infrastructure. This can be very expensive in addition to damaging to an enterprise’s corporate identity.
The integrity of an organization’s private keys, throughout the infrastructure from root to issuing CAs, provides the core trust foundation of its PKI and, as such, must be safeguarded. The recognized best practice for securing these critical keys is to use a FIPS 140-2 Level 3 certified hardware security module (HSM), a tamper-resistant device that meets the highest security and assurance standards.

What is inadequate separation (segregation) of duties for PKIs?

Weak controls over the use of signing keys can enable the certification authority (CA) to be misused, even if the keys themselves are not compromised. A malicious actor might issue malicious certificates that allow a device or user to impersonate a legitimate user and conduct a man in the middle attack, or to digitally sign malware that is then propagated, because it appears to come from a trusted source.
Proper security controls need to be established when designing an organization’s public key infrastructure (PKI). Security for PKIs should include separating CA roles and setting policies so that the operation fails if an individual attempts to perform more than one CA role. When setting up PKIs, policies and procedures to ensure proper separation of duties, including establishing contingencies when a team member leaves, is critical to the security and integrity of the PKIs and must be part of the initial design. It is preferable to implement a technology that enables a technical solution to the separation of duties policy. For example, presentation of an “K of N” smart card set can enforce a robust separation of duties policy by simply not allowing an individual to issue certificates without the presence of, for example, a security officer.

What is insufficient scalability in a PKI?

A public key infrastructure (PKI) that fails to factor in the growth of the organization and its users will eventually need to be redesigned as the business scales, meaning lost productivity and customer impact. With new applications coming online daily and many users demanding access via multiple devices, good business planning requires that PKI scalability be considered from the outset.
Many organizations will need more than one certification authority (CA) to meet their growing requirements — certificates are used for logon authentication, digital document signing, email, and more. A root CA can act as the “master” with multiple subordinate CAs covering the various use cases. Alternatively, the organization can plan for scale by establishing multiple root CAs and multiple hierarchies. Regardless of the strategy, the goal is to get it right the first time to ensure an organization’s PKI can keep up with its growing needs.

What is subversion of online certificate validation?

Subversion of online certificate validation processes can enable malicious use of revoked certificates. An attacker who can prevent a certificate from reaching the certificate revocation list can impersonate a legitimate actor and execute malicious activity, while the victim is unaware that he/it is communicating with an illegitimate participant.
Defining certificate authentication policies and procedures is an instrumental part of a public key infrastructure’s (PKI) design. Further, proper execution and enforcement will ensure that revoked certificates — and users — are denied access. While many organizations will use a certificate revocation list (CRL), some might opt for a different approach, such as online certificate status protocol (OCSP) or authentication, authorization and accounting (AAA).
Such decisions need to be part of the initial design discussions based on the needs of the organization. It is worth noting that any private keys deployed in the certificate revocation process need to be protected equally with the keys that form the basis of the issuing process.


What is lack of trust and non-repudiation in a PKI?

A public key infrastructure (PKI) with inadequate security, especially referencing key management, exposes the organization to loss or disruptions, if the organization cannot legally verify that a message was sent by a specific user.
A PKI built with security and integrity at its core can provide you with legal protection in instances, when user activity is in dispute. The secure digital signature provides irrefutable evidence of the message’s sender and message’s content, but it is only as defendable as the PKI is strong. By demonstrating that signing keys are adequately protected all the way back to the root key, your organization can withstand any legal challenge about the authenticity of a specific user and their actions.

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