PKI Reading Time: 11 minutes

Everything you need to know about Microsoft PKI

Currently, PKI is used by enterprises to handle security through encryption. The most popular type of encryption currently in use entails two keys: a public key, which anybody may use to encrypt messages, and a private key, sometimes known as a secret key, which should only be accessible to one person. Apps, devices, and people can all use these keys. 

In the 1990s, PKI security first appeared to help control encryption keys through the issue and administration of digital certificates. The certificates are the equivalent of a digital license or passport. To preserve security, these PKI certificates confirm the owner of a private key and the validity of that relationship moving forward.

Messages are encrypted and decrypted using highly advanced mathematical calculations known as cryptographic algorithms. They serve as the foundation for PKI authentication. By today’s standards, symmetric encryption is a simple cryptographic technique, yet it was formerly thought to be cutting-edge. In fact, during World War II, the German army utilized it to relay secret messages. The Imitation Game, a film, does a decent job of describing the operation of symmetric encryption and its significance throughout the conflict.

Why we need PKI

Verifying a certificate chain entails confirming that a specific certificate chain is reliable, authentic, and correctly signed. The following process verifies a certificate chain beginning with the certificate submitted for authenticity.

Typically, the chain of certificates going up to the Root CA is submitted with the certificate of a client whose validity is being evaluated. Using the issuer’s public key, the verifier examines the certificate. The issuer’s certificate follows the client’s certificate in the chain, where the issuer’s public key is located. If the higher CA, who signed the issuer’s certificate, is trusted by the verifier, the verification procedure is now considered successful.

How Does PKI Work

Keys and certificates are two technologies that are implemented in PKI.

  • A key is a substantial number used for encryption.
  • The key formula is used to encrypt every component of a message. Someone who possesses this key will be able to decrypt what appears to be a meaningless message. For Example, A will become B, for instance, if you want to construct a message where the one replaces each letter after it. After C comes D, etc.
  • PKI uses two keys: a private key and a public key.
  • Once you receive the message, you decode it using a private key. The connections between the keys are made via a challenging mathematical equation. Although the private and public keys are linked, this difficult calculation makes the connection possible. Because of this, it is very challenging to determine the private key using information from the public key.

Symmetric Encryption

The term “symmetric encryption” refers to a method of message encryption and decryption that uses the same key. A message entered in plain text with symmetric encryption is encrypted after going through a series of mathematical permutations. The same plain text letter sometimes appears different in the encrypted message, making it challenging to decrypt. For instance, the phrase “HHH” would not be encrypted to the same three characters. The fact that the same key must be used to encrypt and decode the message carries significant risk, even though decrypting messages without the key is extremely challenging. That’s because the system for sending secure messages breaks if the channel used to distribute the key is compromised.

Here are a few of the best encryption algorithms that you may use to protect sensitive data.

  • Advanced Encryption Standard (AES)

    The symmetric encryption algorithm Advanced Encryption Standard encodes data blocks of 128 bits at a time. These data blocks are encrypted using keys with lengths of 128, 192, and 256 bits. Data encryption takes 14 rounds for a 256-bit key, 12 rounds for a 192-bit key, and ten rounds for a 128-bit key. Each cycle includes several stages for substitution, transposition, plaintext mixing, and other operations.

  • Triple Data Encryption Standard (DES)

    The Data Encryption Standard (DES) approach encrypts data blocks with a 56-bit key using a symmetric encryption technique called Triple DES. Each data block is encrypted using the DES cipher method three times in Triple DES. ATM PINs and UNIX passwords can both be encrypted using Triple DES. Well-known programs like Mozilla Firefox and Microsoft Office also use triple DES.

Asymmetric Encryption

The exchange issue that hampered symmetric encryption is resolved by asymmetric encryption, also known as asymmetrical cryptography. It accomplishes this by generating two unique cryptographic keys -a private key and a public key – hence the name “asymmetric encryption.” A message is encrypted using mathematical permutations in asymmetric encryption. It must be decrypted using a private key that the receiver should only know, and it must be encrypted using a public key that can be distributed to anyone.

For Example: Using Bob’s public key, Alice creates encrypted ciphertext that only Bob’s private key can decrypt to send Bob a private message. If Bob ensures that no one else has access to his private key, Alice can confidently transmit the message that nobody else will be able to read it, not even an eavesdropper. Another action that is more difficult to do with symmetric encryption is the use of digital signatures, which function as follows: 

Bob can use his private key to send Alice a message that includes an encrypted signature. When Alice receives the message, she can confirm two things using Bob’s public key. The message was sent by Bob or someone using Bob’s private key. Because if the communication is changed even when in transit, the verification will not be successful.

In both instances, Alice has yet to produce a key on her own. Alice can communicate with Bob using encryption and verify documents that Bob has signed using only a public key exchange. Importantly, these activities only work in one direction. Alice would have to create her private key and share the accompanying public key to undo the activities, so Bob could send private messages to Alice and confirm her signature.

This procedure creates two 1024-bit long prime numbers and multiplies them together. The two prime numbers used to construct the answer are the private key, while the answer is the public key.

This method works because, when two prime integers of that size are involved, it is very difficult to reverse the computation, making it relatively simple to compute the public key from the private key but very impossible to compute the private key from the public key.

The fact that Public Key Infrastructure (PKI) uses a pair of keys to delivering the underlying security service is its most distinctive feature. The private key and public key make up the key pair.

Since the public keys are in the public domain, misuse is likely. Thus, reliable infrastructure must be created to manage these keys.

Algorithm used to protect the Sensitive information are as follows:

Rivest-Shamir-Adleman (RSA)

An asymmetric encryption scheme called Rivest-Shamir-Adleman is based on the factorization of the product of two enormous prime integers. Only someone aware of these numbers can effectively decipher the message. Data transmission between two communication locations is frequently secured using RSA. However, it becomes less effective when encrypting vast amounts of data. Nevertheless, because of its unique mathematical characteristics and complexity, this encryption technology is particularly trustworthy in delivering sensitive data.

PKI certificates

PKI provides public key assurance. It offers public key distribution and key identification. The following components form the structure of PKI.

Digital Certificate

People use ID cards like a passport or driver’s license to establish their identification. With one exception, a digital certificate performs the same fundamental function in the electronic environment.

Digital Certificates can be granted to computers, software programs, or anything else that must establish its identity in the electronic world in addition to individuals. The ITU standard X.509, which outlines a common certificate format for public key certificates and certification validation, is the foundation for digital certificates. As a result, X.509 certificates are another name for digital certificates. The Certification Authority stores the user client’s public key in digital certificates (CA)

Certifying Authority (CA)

The CA provides a client with a certificate and helps other users to validate the certificate. The CA is responsible for accurately verifying the client’s identity requesting a certificate, checking that the certificate’s contents are accurate, and digitally signing it.

Key Functions of CA

The key functions of a CA are as follows –

  • Generating key pairs

    The client and the CA can work together or independently to create a key pair.

  • Issuing digital certificates

    The CA could be compared to the PKI version of a passport office; after receiving the credentials needed to verify the client’s identity, the CA issues the certificate. The CA then signs the certificate to prevent alterations to the information it contains.

  • Publishing Certificates

    The CA must publish certificates so users can find them. There are two ways of achieving this. One is to publish certificates in the equivalent of an electronic telephone directory. The other is to send your certificate to those you think might need it by one means or another.

  • Verifying Certificates

    To facilitate the verification of his signature on clients’ digital certificates, the CA makes its public key available in the environment.

  • Revocation of Certificates

    When the user compromises their private key or the CA loses trust in the client, the certificate may be revoked. Following revocation, CA keeps a list of every certificate that has been revoked and is accessible to the environment.

How the Certificate Creation Process Works

Asymmetric encryption is frequently used during the certificate creation process, which operates as follows:

  • A private key is generated, and the associated public key is calculated.
  • The CA requests and verifies any personal information about the owner of the private key.
  • The owner of the private key signs the Certificate Signing Request (CSR) to attest to their ownership of the public key. The issuing CA then verifies the request and signs the certificate using the CA’s private key.

Components of PKI Ecosystem

The Certificate Authority is a business that creates reliable certificates recognized by a wide range of software applications, most notable browsers like Google Chrome, Safari, Firefox, Opera, and the Xbox 360.

  • The Registration Authority

    usually, this entity does the validation. After completing all the necessary preparation, it will send the request to the CA to issue the certificate. The RA might be a business, an application, or a part.

  • Relying Party

    Is the individual at the website who is using the certificate. The subscriber is the website owner who is purchasing the certificate.

The architecture of PKI

Two-Tier Architecture

Most businesses would discover that a two-tier architecture is a practical design. The root CA is on the first tier, which should remain offline .Since we separate the roles of the Root CA and Issuing CA, security is improved. Under it, Subordinate Issuing CA should be functioning.

  • A two-tier architecture also improves flexibility and scalability, improving fault tolerance. Being offline helps Root CA better safeguard its private keys and reduces the likelihood that they will be compromised. Because the roles are distinct, we can build numerous issuing CAs and put them behind a load balancer.

Three–Tier Architecture

A three-tier architecture is similar to a two-tier system in that it has an offline root CA at the top and an online issuing CA at the bottom. Still, the offline root CA is now held by an intermediary layer. The policy CA, which sets the requirements that must be fulfilled before a certificate is given, may be the intermediate CA.

  • Any authenticated user can obtain a certificate, albeit certificate acceptance can necessitate the user’s physical presence.
  • Three-tier PKI does boost security, scalability, and flexibility but comes at an additional expense and manageability.
  • However, if an issuing CA faces compromise or something similar, the second level can revoke the certificates while keeping the other branches active.

What Are Some Typical Challenges

When hackers attempt to employ MITM attacks to intercept, modify, or steal information, this is one of the key issues PKI tries to solve. The “person” trying to get in the way doesn’t have the private key. Thus, he can’t decrypt the message. Their best effort is, as a result, intercepted. 

  • A large amount of processing power is needed to decipher 2048-bit encryption. PKI is a strong defense against these kinds of online attacks as a result.
  • PKI also addresses the issue of managing certificates. It achieves this by confirming the truth of each one through validation. False certificates lost or stolen can also be removed using PKI. In addition, certificates may be revoked.

Components of PKI Ecosystem

The Certificate Authority is a business that creates reliable certificates recognized by a wide range of software applications, most notable browsers like Google Chrome, Safari, Firefox, Opera, and the Xbox 360.

  • The Registration Authority

    usually, this entity does the validation. After completing all the necessary preparation, it will send the request to the CA to issue the certificate. The RA might be a business, an application, or a part.

  • Relying Party

    is the individual at the website who is using the certificate. The subscriber is the website owner who is purchasing the certificate.

Hierarchy of CA

single trustworthy CA from whom all users receive their certificates is realistically impractical, given the size of the networks and the demands of global communications. Second, having only one CA available could be problematic if that CA were to get hacked. The hierarchical certification architecture is valuable in this situation because it permits the usage of public key certificates in settings where two communicating parties do not share a trust relationship with a common CA.

The root CA is the highest level of the CA hierarchy, and its certificate was self-signed. The root CA signs the CA certificates for the CAs that are directly subordinate to it (for example, CA1 and CA2).

The higher-level subordinate CAs sign the CA certificates for the CAs that are subordinate to them in the hierarchy (for example, CA5 and CA6). Hierarchies of certificate authorities (CAs) are reflected in certificate chains. A certificate chain shows the sequence of certificates that led from a hierarchy branch to its root.

Verifying a certificate chain involves ensuring that a particular certificate chain is legitimate, properly signed, and reliable. The verifier takes the certificate using the issuer’s public key. The issuer’s certificate, which is in the chain next to the client’s certificate, contains the issuer’s public key. 


Only a complete public key infrastructure can achieve the goal of creating and maintaining a trustworthy environment for systems management while also providing a workable, transparent, and automatic foundation. Significant gains can be made from an interest in PKI due to decreased costs, streamlined corporate processes, and enhanced customer service. Focusing on particular business applications will enable your public key infrastructure to help you achieve the desired financial success. Virtual private networks, access control, e-commerce, web-based security, desktop security, and secure email can all be provided via your current network.

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About the Author

Ambika Rastogi is a Consultant at Encryption Consulting, working with PKIs, HSMs, and working as a consultant with high-profile clients.

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