PKI Glossary

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See TDEA and DES


Active Directory is the name of the Microsoft directory product.


Active Directory Certificate Services is the name of the Microsoft CA product.


Advanced Encryption Standard also known by its original name Rijndael is a specification for the encryption of electronic data established by the U.S. National Institute of Standards and Technology (NIST) in 2001.

Authority Information Access Point (AIA)

The authority information access extension indicates how to access information and services for the issuer of the certificate in which the extension appears. Information and services may include on-line validation services and CA policy data.


The authority information access extension indicates how to access information and services for the issuer of the certificate in which the extension appears. Information and services may include on-line validation services and CA policy data.


Abstract Syntax Notation One (ASN.1) is a standard interface description language (IDL) for defining data structures that can be serialized and deserialized in a cross-platform way. It is broadly used in telecommunications and computer networking, and especially in cryptography.

Asymmetric Encryption

Asymmetric Encryption is an encryption system that uses two keys, a public-private key pair for encryption and decryption, as well as for digital signatures. Common asymmetric algorithms are RSA, Diffie-Hellman, and ECDSA, and DSS/DSA.


Certificate Authority The entity in a Public Key Infrastructure (PKI) that is responsible for issuing public-key certificates and exacting compliance to a PKI policy. Also known as a Certification Authority.


Card Application Management System is a system that can manage applications on smartcards


While CAPI can stand for Common Application Programming Interface, in the context of PKI is it most often referred to as MS-CAPI and stands for Cryptographic Application Programming Interface. CAPI is an application programming interface included with Microsoft Windows operating systems that provides services to enable developers to secure Windows-based applications using cryptography. It is a set of dynamically linked libraries that provides an abstraction layer which isolates programmers from the code used to encrypt the data.


CRL Distribution Point A pointer to where CRL’s are to be published.


A digital representation of information which at least (1) identifies the certification authority issuing it, (2) names or identifies its Subscriber, (3) contains the Subscriber’s public key, (4) identifies its operational period, and (5) is digitally signed by the certification authority issuing it.

Certificate Template

Certificate templates is a Microsoft Term used to set the format and content of type of certificate to be produced on a CA. Configurations include enrolment permissions, renewals, certificate purpose, lifetime, key length, extensions, issuance requirements, etc. When used in a Windows enterprise environment, Certificate Templates exist in the certificate templates container of Active Directory. X.509 attribute extensions are used to define a template’s structure.


Certificate Lifecycle Management is software that allows for the management of certificates throughout their lifecycle


Card Management System is software that allows for the management of smartcards and tokens.


Common Name is the name in a certificate for the entity being issued the certificate.


Crypto Next Generation is a term used by Microsoft to describe a technology introduced in Windows Server 2008 that enables hardware and software vendors to interface with Microsoft crypto capability


Certificate Policy. The governing policy for the PKI service and all of its components. This document includes the governing attributes such as CA and end-entity certificate lifetimes, CRL requirements and authorised certificate usages and reliance


Certificate Practices Statement . This document that outlines all of the accepted practices for the management of the PKI services and all of the components including how to manage the Root CA and Issuing CAs, key roles and responsibilities, creation of CA certificates and CRLs, enrolment and approval of end-entity certificates, publication and reliance upon CRLs by relying parties. The CPS is supported by operational procedures and work instructions

Credential Roaming

Credential Roaming is where a user certificate and protected credential information is roamed between computers allowing for the prevention of excessive enrollment by users on multiple computers and loss of certificates if a user’s profile is deleted.


Certificate Revocation List A list of all of the reported compromised certificates that have been issued by the CA, that would otherwise be considered valid. A CRL does not contain expired certificates, as they should not be considered valid.

CRL Overlap Period

A CRL Overlap period is set on the CA to allow time to perform Emergency CRL Signing or to recover the CA before the last CRL expires. The CRL Overlap configuration is set for 1 days, for example, and the base CRL next. Update setting is 9 days, then the CRL is valid for a total of 10 days from issuance. This would allow for a 9 day recovery window.

Cross Certification

Cross certification enables entities in one public key infrastructure (PKI) to trust entities in another PKI and establish an agreement of responsibilities and liability of each party. The cross certificates can also implement rules to limit trust such as name constraints.


Crypto Service Providers are typically a .dll and signature file referenced in the registry and provide cryptography services used in data signing and hashing along with the generation, protection, and storage of key material.


Certificate Signing Request What the end-entity provides the CA, includes the public key and all of the naming components that need to be added to the certificate.


Certificate Trust List

Delta CRL

A Delta CRL contains the list of revoked certificates since the last base CRL issuance to allow clients to maintain knowledge of revocation while using less bandwidth for that knowledge. Delta CRLs are useful if there’s a lot of revocation happening that then means a large CRL to download, but less often. The disadvantages of using Delta CRLs include the fact that not all services and systems understand them, as well as the time it takes for a client to read both the newest Delta CRL and the Base CRL to verify the freshest revocation list. For these reasons, we don’t recommend employing Delta CRLs in most PKI implementations.


Distinguished Encoding Rules is a restricted variant of Basic Encoding Rules for producing unequivocal transfer syntax for data structures described by ASN.1.


Data Encryption Standard is a symmetric-key algorithm for the encryption of digital data. Although its short key length of 56 bits makes it susceptible to attack and is no longer considered secure. DES evolved into 3DES or TDEA but this has also been found to be susceptible to compromise.


Diffie–Hellman key exchange is a mathematical method of securely exchanging cryptographic keys over a public channel. DH is one of the earliest practical examples of public key exchange implemented within the field of cryptography being first published in 1976.


A digest is the output produced by a hash function after it processes a message.

Digital Signature

A digital signature is a cryptographic technique that uses a mathematical algorithm that binds a sender’s identity to a digital message or document based on a subscriber’s private key. It secures the message or document and verifies the integrity of the signature allowing a Relying Party to be sure that the file or document has not been altered or interfered with.


Distinguished Name is a set of values based on the X.500 or LDAP standards. A DN often is forms the Subject but can also be seen in a number of other places like the SAN, AIA and CDP

Document Signing

Document signing applies a digital signature to a document. The digital signature verifies the identity of the user that signed the document, ensuring the signer cannot later claim that they signed it. Typically, this is either the last person to edit the document before distribution or the person that verifies that the content represents the views of the organization distributing the document. Digital signing also allows a recipient to verify that content of the document was not modified after the digital signature was applied to the document.


Disaster Recovery is the process followed when a major event affects the operation of services.


Disaster Recovery and Business Continuity Plan is the plan that tells operators what to do in an emergency.


Digital Signature Algorithm is an algorithm used to perform digital signatures as per the X.509 standard


Extensible Authentication Protocol (EAP) is an authentication framework frequently used in network and internet connections.


Elliptic Curve Cryptography ECC is an approach to public-key cryptography based on the algebraic structure of elliptic curves over finite fields. ECC allows smaller keys compared to non-EC cryptography (based on plain Galois fields) to provide equivalent security.


Elliptic-curve Diffie–Hellman (ECDH) is a variant of the Diffie–Hellman protocol using elliptic-curve cryptography. ECDH is a key agreement protocol that allows two parties, each having an elliptic-curve public–private key pair, to establish a shared secret over an insecure channel. This shared secret may be directly used as a key, or to derive another key. The key, or the derived key, can then be used to encrypt subsequent communications using a symmetric-key cipher.


Elliptic Curve Digital Signature Algorithm is a Digital Signature Algorithm that uses keys derived from elliptic curve cryptography that efficiently provides equivalent security. It provides RSA-level security but with much smaller key sizes. For example, an ECDSA 256-bit key size secures better than the RSA 2048. The decreased bandwidth in key exchanges is an obvious advantage of ECDSA.


End Entity is a certificate issued to user or device that will use the certificate and private key pair.


Encrypted File System


Enhanced Key Usage is both a certificate extension and a certificate extended property value.


Evidence of Identity is the process and documents required to prove a person’s identity.


Extended Validation certificates are used for HTTPS websites and software. The registration process for these certificates validates the legal entity controlling the website or software package.


Federal Information Processing Standards are standard produced by NIST in order to give some assurance on if something can be trusted.


Fully Qualified Domain Name is usually the name given to a device which includes the hostname of that device.


A Hash is a digital finger print designed to allow a user to secure authentication and ensures data message integrity across digital channels


Hardware Security Module The HSM is a trusted network computer where the cryptographic processes that PKI requires to remain secure and can be used virtually or on a cloud environment.


HyperText Transport Protocol – Secure Hypertext Transfer Protocol Secure is an extension of the Hypertext Transfer Protocol. It is used for secure communication over a computer network and is widely used on the Internet. In HTTPS, the communication protocol is encrypted using Transport Layer Security.


An Intermediate CA is a CA that is subordinate to another CA and issues certificates to other CAs in the CA hierarchy. These can be Issuing CAs and Policy CAs depending on the PKI design.


Information Security Manual – The ISM is produced by the Australian Signals Directorate. The purpose of the ISM is to outline a cyber security framework that an organisation can apply, using their risk management framework, to protect their systems and data from cyber threats.



Information Security Manual – The ISM is produced by the Australian Signals Directorate. The purpose of the ISM is to outline a cyber security framework that an rganization can apply, using their risk management framework, to protect their systems and data from cyber threats.


Issuance is the act of an Issuing Authority in creating a certificate that is bound to a subscriber.  The process requires authentication of the subscriber and/or subject


Information Technology


Kerberos is a protocol that defines how clients interact with a network authentication service and builds on symmetric key cryptography and optionally may use public-key cryptography during certain phases of authentication.

Key Archival

Key archival is where a private key is archived to allow a user who has lost their private key to recover encrypted data. This should only be done with encryption keys, not signing keys. Within Microsoft AD CS the use of a Key Recovery Agent allows a certificate’s public key to encrypt a private key so that it can be stored as a blob in the CA database, smartcard, or HSM and retrieved at a later date. This requirement is specified in a template.

Key Pair

In an asymmetric cryptosystem, a key pair consists of a private key and its mathematically related public key having the property that the public key can verify a digital signature that the private key creates.


Layer 2 Tunneling Protocol – is a unnelling protocol used in creating VPN connections. However, it only provides unnelling – bundling up data for private transportation over public networks. For VPN functionality, it uses Ipsec, which provides encryption and confidentiality.


Lightweight Directory Access Protocol (LDAP) is a vendor-neutral software protocol used to lookup information or devices within a network.


Levels of Assurance are the levels you can trust something to based on the assurance that has gone into the trust of that service.

M of N Authentication

The MofN feature provides a means by which organizations employing cryptographic modules for sensitive operations can enforce multi-person control over access to the cryptographic module, or selected aspects of it. MofN involves a splitting of an authentication secret into multiple parts or splits. The shared secret is distributed (or “split”). Further information:


Multi-Factor Authentication is authentication using more than one form such as something you have (a card or USB key), something you know (username and password) or something you are (biometric authentication).

Name Constraints

The Name Constraints extension is used in CA certificates. It specifies the constraints that apply on subject distinguished names and subject alternative names of subsequent certificates in the certificate path. These constraints can be applied in the form of permitted or excluded names.


Network Device Enrolment Service NDES allows software on routers and other network devices running without domain credentials to obtain certificates based on the Simple Certificate Enrolment Protocol (SCEP).


National Institute of Standards and Technology is a United States Federal Government standards body. NIST run a laboratory where they test, develop and recommended standards and best practices for Government such as FIPS.


Non-repudiation refers to the inability of signers to deny that a signature is theirs. The secure digital signature provides irrefutable evidence of the message’s sender as well as the time it was sent, but it is only as defensible as the PKI is strong.


A nonce is a randomly generated number that may only be used once. It is used in secure communications to prevent replay attacks. Each packet or conversation is uniquely numbered to ensure both parties are receiving information relating to their request. In PKI, this is optionally used to protect OCSP queries from cached/replay attacks. The signing of a nonce is often used in certificate based authentications.


Online Certificate Status Protocol OCSP is used by Certificate Authorities to check the revocation status of an X. 509 digital certificate.


Object Identifier is a globally unique value used in ASN.1


The Protected Extensible Authentication Protocol, also known as Protected EAP or simply PEAP, is a protocol that encapsulates the Extensible Authentication Protocol (EAP) within an encrypted and authenticated Transport Layer Security (TLS) tunnel. The purpose is to correct deficiencies in EAP.


Pin Entry Device. Enables you to manage the security administration functions on a Thales Luna hardware security module (HSM). The PED device provides the flexibility to administer an HSM locally or remotely, while still maintaining the highest levels of security through FIPS 140-2-validated two-factor authentication.


Privacy Enhanced Mail is a file format for X.509 certificate files using Base64 encoding to store and send keys, certificates, and other data.


Personal Identity Verification is a standard produced by NIST for the storage of identity data on smartcards for Federal Government agencies. It was made a requirement for adoption by Federal Government agencies in Homeland Security Presidential Directive 12. The buying power of Federal Government has made this a defacto industry standard.


Public Key Cryptography Standards is a group of 15 numbered standards developed by RSA but now widely adopted. These standards are defined and published by RSA Security LLC. Some common PKCS techniques are PKCS 7, PKCS 10, PKCS 11 and PCKS 12, which cover things like messaging syntax and formatting for digital certificates and how private keys get stored.


Public Key Enablement is a generic term covering many aspects of the use of PKI


Public Key Infrastructure The framework and services that provide for the generation, production, distribution, control, accounting, and destruction of public key certificates. Components include the personnel, policies, processes, server platforms, software, and workstations used for the purpose of administering certificates and public-private key pairs, including the ability to issue, maintain, recover, and revoke public key certificates

Policy CA

The Policy CA is an Intermediate Subordinate CA typically in the second tier of a three-tier PKI hierarchy placed directly beneath the Root CA. It issues certificates only to other CAs in the hierarchy directly and subordinate to it or two or more levels lower in the hierarchy. These CAs enforce the policies and procedures defined at the Policy CA. In most instances a policy CA is not required.


Point-to-Point Tunneling Protocol (PPTP) is an obsolete method for implementing virtual private networks. PPTP has many well known security issues.


Post-quantum cryptography is the field of cryptography that deals with cryptographic algorithms that can run on classical computers and are secure against an attack by a large-scale quantum computer that runs much stronger and faster. These algorithms have been based on the assumption that the degree to which they are unable to be solved maps to their strength.

Private Key

The secret half of a key pair used in a public key algorithm, private keys are typically used to encrypt a symmetric session key, digitally sign a message, or decrypt a message that has been encrypted with the corresponding public key.

Public Key

The public part of an asymmetric key pair used for public key encryption techniques.  The public key is typically used for verifying digital signatures or to encrypt messages to the owner of the private key. The public key corresponding to a certificate is embedded in the certificate itself.

Public Key Encryption

Public-key encryption uses two separate keys that are mathematically related, to encrypt and decrypt the content. The public key can be distributed widely while the private key remains with the user or device that created the key pair.


Registration Authority validates user information for the CA and can be used to authority certificate creation by the CA after authorisation. It can also be used as a source of EE registration information.


Remote Authentication Dial-In User Service is a networking protocol that provides centralized authentication, authorization, and accounting management for users who connect and use a network service.


Root Certification Authority is the root of the hierarchy of a PKI. A Root CA will have a self signed certificate.


A re-key involves changing out the cryptographic key that is being used in a cryptographic system application. This entails issuing a new certificate with the new public key embedded in it.

Relying Party

A recipient, or certificate user, who acts in reliance on that certificate and/or any digital signatures verified using that certificate, especially the certificate chain.


Repository refers to a location where public CA certs, EE Certs, CRLs, CP, CPS, and other PKI documentation is available for review. It often takes the form of a HTTP website, but can be an LDAP Directory or even an FTP based site.


Repository refers to a location where public CA certs, EE Certs, CRLs, CP, CPS, and other PKI documentation is available for review. It often takes the form of a HTTP website, but can be an LDAP Directory or even an FTP based site.


Revocation of a certificate invalidates a previously signed certificate and is listed in the next published CRL by serial # and date of revocation. A revocation method is essential to a PKI. It ensures the remaining certificates can be trusted.

Role Separation

As fully defined in a Certificate Policy, role separation is a core PKI design principle that sets the requirements for PKI management where no one single person has full control. Depending on the size of the operation of the PKI, separate roles can be as little as CA Administrators/Operators separated with an Operations Manager, with other roles such as Auditor/Security Officer, Platform Support, Registration Officers and Backup Operators all common roles. Role separation should be fully defined in the Certificate Policy.


Rivest Shamir Adleman – the inventors of composite prime group public key encryption and signature algorithms.


Subject Alternate Name


Simple Certificate Validation Protocol is another protocol for the validation of certificates


Simple Certificate Enrolment Protocol SCEP, is a protocol that allows devices to easily enrol for a certificate by using a URL and a shared secret to communicate with a PKI.

Self-Signed Certificate

A self-signed certificate is a certificate that uses its public key to verify its own signature and where the subject name is identical to the issuer name.  A Root CA uses a self-signed certificate in its establishment as the root of trust in the PKI.

Session Key

Session keys are used in single communication settings usually using symmetric encryption. They are short-lived and discarded when no longer needed. Used for encrypting and decrypting large amounts of data, they are also employed in the public-private key exchange for sending and receiving messages in that process. An example of a protocol that uses session keys is TLS.


Secure Hash Algorithm SHA hash functions are used by Certificate Authorities when signing Certificate Revocation Lists and Digital Certificates. A Secure Hash Algorithm is meant to generate unique hash values from files.


Secure/Multipurpose Internet Mail Extensions) is a standard for public-key encryption and signing of MIME data. S/MIME was originally developed by RSA Data Security, but is now maintained as part of IETF standards. It is defined in a number of documents, most importantly RFC 8551


Either comes in a credit card-sized hardware token chip or USB form factor. It incorporates one or more integrated circuit (IC) chips to implement cryptographic functions, has inherent resistance to tampering, and stores private keys. A PIV is a US Government issued smartcard with a picture image and storage of certificates and biometrics.


Secure Sockets Layer is an older form of HTTPS authentication and encryption and is used exclusively for HTTPS traffic.


Secure Socket Tunneling Protocol, is a VPN protocol that creates a tunnel between a client device and a server. Primarily, SSTP is used to secure remote access to private networks over the internet.


A subscriber is an entity that enrolls for a certificate from an Issuing CA and bears ultimate responsibility for the use of the private key associated with the certificate. These responsibilities are detailed in the Certification Practice Statement (CPS) and the Certificate Policy (CP).

Suite B

Suite B is a set of advanced cryptographic algorithms promulgated by the National Security Agency as part of its Cryptographic Modernization Program. Protocols included are AES, SHA-2, ECDH, and ECDSA


Triple Data Encryption Algorithm is a symmetric-key block cipher, which applies the DES cipher algorithm three times to each data block. The Data Encryption Standard’s (DES) 56-bit key is no longer considered adequate in the face of modern cryptanalytic techniques and supercomputing power. A CVE released in 2016, CVE-2016-2183 disclosed a major security vulnerability in DES and 3DES encryption algorithms. This CVE, combined with the inadequate key size of DES and 3DES, led to NIST deprecating DES and 3DES for new applications in 2017, and for all applications by the end of 2023.[1] It has been replaced with the more secure, more robust AES.


The thumbprint is a unique hash value using the SHA-1 algorithm that uniquely identifies a certificate. It is computed over the complete certificate, which includes all its fields, including the signature, and is unrelated to the hash used in the digital signature, thus it is unique everywhere. Although a serial number is unique to a CA, it may not be unique everywhere since the same number could be computed from another CA.


Time-stamping is used often in Code Signing or Document Signing and creates a notation that indicates, at a minimum, the correct date and time of an action or activity and the identity of the entity that created the notation.

Time-Stamping Server

A Time-Stamping Server is a server or service issuing time-stamps for use by other entities.


Transport Layer Security can be used for authentication and encryption but is newer than SSL and can be used for protocols including but not limited to HTTPS.


Trusted Platform Module (TPM) is an international standard for a secure cryptoprocessor, a dedicated microcontroller designed to secure hardware through integrated cryptographic keys. The term can also refer to a chip conforming to the standard ISO/IEC 11889.


Validation Authority is a sub-component of CA function that works in.


Validation is the process by which an end-entity certificate certifies information in a certificate to confirm it’s authenticity. This can include checking the chain of trust in a PKI, the date of expiry of a certificate, ensuring the certificate has not been revoked or tampered with.

Validity Period

The period that is defined within a certificate or CRL, during which that certificate or CRL is intended to be valid. For a certificate, it generally begins when the certificate is issued and ends at the end date embedded in the certificate unless it is revoked or suspended earlier.


A VPN, or Virtual Private Network, is a tool that encrypts your internet traffic and hides your IP (Internet Protocol) address to ensure a secure and private connection to the internet. This prevents third parties from snooping or collecting data about your activity because all information stays hidden behind a code.


X.509 is an International Telecommunication Union (ITU) standard defining the format of public key certificates. X.509 certificates are used in many Internet protocols, including TLS/SSL, which is the basis for HTTPS, the secure protocol for browsing the web. They are also used in offline applications, like electronic signatures.