Comparing Kerberos Vs NTLM Vs LDAP – Must Know DIFFERENCES

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Quick Answer

LDAP is a protocol designed for efficiently accessing and retrieving information stored within directory services. Kerberos and NTLM are purely authentication mechanisms used for secure access to directory services.

Directories play a pivotal role in managing and organizing vast amounts of data within an organization.

AD diagram

Active Directory (AD) is Microsoft’s directory service solution, primarily designed for managing user identities and network resources in a Windows environment.

LDAP, Kerberos, and NTLM are protocols that integrate with directory services to ensure secure access to these resources.

LDAP (Lightweight Directory Access Protocol) is a protocol that can handle both user authentication and directory information access.

ldap diagram

LDAP works well with structured data, as it is specifically designed for organizing and accessing directory information in a hierarchical and standardized format. Due to this, LDAP can be used as an authentication mechanism to validate credentials against entries in a database. An LDAP authentication transaction is relatively straightforward, it receives credentials and authenticates them against user data within the LDAP directory database.

Although it can be used as an authentication mechanism similar to Kerberos and NTLM it lacks some of the advanced security features and flexibility. The most common usage of LDAP is solely for querying directory services like Microsoft AD. These directories organize and store structured data, including user information, attributes, and object classes. LDAP enables applications to efficiently query and retrieve data from these directories.

Kerberos is an authentication protocol designed to secure network resources. In a Kerberos system, a user is issued an encrypted ticket, known as the Ticket Granting Ticket (TGT), by a component called the Key Distribution Center (KDC). The KDC comprises two main servers: the Ticket Granting Server (TGS) and the Authentication Server (AS).

kerberos diagram

When integrated with Active Directory, Kerberos uses AD as the central identity provider and repository for both user and service account information; otherwise, it maintains its own separate database.

Once a TGT is obtained, it is stored in the user’s cache and can be used to request additional tickets for accessing Kerberos-enabled services and resources. Kerberos provides a robust and secure authentication mechanism, enabling single sign-on and reducing the need for transmitting plaintext passwords.

NTLM (New Technology LAN Manager), specifically NTLMv2, is an authentication protocol primarily used in Windows environments. It employs an HMAC-MD5 hash and a three-step negotiation process to authenticate users. However, NTLM is considered less secure than Kerberos and is gradually being phased out in favor of Kerberos. NTLM is still used in legacy systems for compatibility reasons.

How LDAP Works

LDAP (Lightweight Directory Access Protocol) serves as a protocol for efficient interaction with directory servers over TCP/IP. This open standard protocol is compatible and flexible across a variety of directory servers and client APIs, offering resource-efficient data handling and authentication options.

At its core, LDAP revolves around structured entries that represent entities. These entries encompass three fundamental components:

  1. Distinguished Name (DN): This uniquely identifies an entry within the directory tree.
  2. Attributes: These store data with well-defined attribute types and corresponding values.
  3. Object Classes: These define the schema for entries, specifying which attributes an entry of that class should possess.
ldap entry diagram

Directory servers organize data in a hierarchical, tree-like structure and rely on entries as the foundational building blocks. Each entry is characterized by a unique DN, composed of relative distinguished names (RDNs). RDNs are made up of attributes paired with associated values separated by commas. These attributes define various characteristics of the entity and must conform to attribute types outlined in the LDAP schema.

LDAP leverages object classes to create the structure of entries and their attributes, promoting uniformity and data consistency. LDAP’s simplicity and lightweight design render it an accessible choice for a wide range of applications and systems.

The LDAP authentication process uses the client-server model. Both LDAPS (LDAP over SSL) and STARTTLS (LDAP over TLS) are secure variations of LDAP that encrypt the authentication process. When a user enters their login details into a device, these credentials are sent to an LDAP server. The LDAP server then cross-references these credentials with those stored in its database. If there’s a match, authentication is granted.

ldap auth diagram

Notably, LDAP’s query-based authentication method differs from both Kerberos and NTLM. LDAP authentication, while less secure in certain contexts, remains popular in on-premises systems. While LDAP’s most common use case centers on querying directory services, it can also be used for authentication purposes.

How Kerberos Works

Kerberos is a back-end authentication system used in environments where client accounts require authentication for accessing information.

Kerberos was initially developed by MIT computer scientists and later adopted by various organizations, including Microsoft. It represents a significant improvement over NTLM in terms of security, thanks to its ticketing system and robust cryptography which make it more challenging for hackers to gain unauthorized access to a network.

Here are the essential steps in a client’s authorization process within a Kerberos-enabled environment:

  1. Client Initiation: The authentication process begins with the client requesting an Authentication Ticket (TGT) from the Key Distribution Center (KDC).
  2. Identity Verification: The KDC verifies the user’s identity by querying Active Directory (AD).
  3. TGT Issuance: Upon successful verification, the Ticket Granting Service (TGS), a component of the KDC, encrypts the TGT using a secret key and sends it back to the client, along with a session key.
  4. Ticket Storage: The TGT is stored on the client’s system and has a limited validity period.
  5. Resource Access: When the client intends to access a specific resource (referred to as a Service Principal Name or SPN), it communicates with the TGS, providing the TGT and the SPN.
  6. Validation and Session Key: The KDC validates the TGT and, if successful, issues a session key tailored for that particular service.
  7. Access: With the session key, the client gains access to the desired service without the need to re-enter credentials.
kdc diagram

Kerberos is highly regarded for its strong encryption algorithms which protect tickets and passwords.

It offers the convenience of Single Sign-On (SSO), a valuable feature in modern workplaces that allow users to prove their identity only once to Kerberos. Kerberos then securely passes their TGT to other services and machines, eliminating the hassle of repeated logins across various resources.

How NTLM Works

In contrast to Kerberos’s ticket-granting system, NTLM (NT LAN Manager) employs a challenge-response mechanism for authentication. As of 2010, Microsoft has discouraged the use of NTLM in applications due to its well-known vulnerabilities. Unauthorized access to an NTLM-authenticated system can be relatively swift for determined hackers.

NTLM authentication operates through a series of three steps:

  1. Initiation: The client initiates a connection with the network by sending a negotiate message to the server.
  2. Challenge: The server responds with a challenge message to identify the client.
  3. Authentication: The client replies to the challenge with an authenticate message, completing the authentication process.

NTLM provides a form of single sign-on (SSO) that allows user authentication without transmitting passwords in plaintext. The authentication process in NTLM unfolds as follows:

  1. A user inputs their credentials and domain name into a client device.
  2. The client hashes the password.
  3. The client sends the plaintext username and hashed passwords to a server.
  4. The server responds with a random 16-byte number as the challenge.
  5. The client encrypts this challenge using the password hash and forwards it as the response.
  6. The server submits the challenge and response to the domain controller (DC).
  7. The DC retrieves the client’s password, encrypts it with the challenge (similar to the client’s step 5), and verifies the match.
ntlm diagram

However, NTLM exhibits several known vulnerabilities that make its use risky. It lacks support for multi-factor authentication (MFA) and relies on outdated encryption algorithms. These weaknesses in password hashing and encryption render NTLM susceptible to various types of attacks.

NTLMv2 is the newest version of NTLM. The key difference is that NTLMv2 uses a variable-length challenge that is considerably longer and more complex than the fixed 8-byte challenge used in the original NTLM protocol. Also, the client, in addition to using its password hash, includes other data such as the current timestamp and its username when generating the response. Although NTLMv2 is a massive improvement, Kerberos is still the more secure authentication method.


LDAP, Kerberos, and NTLM are components of network security and authentication, each serving distinct purposes. LDAP stands as a protocol for accessing directory services and efficiently managing structured data. LDAP authentication uses a query-based system to verify users. Kerberos, with its ticketing system and encryption, offers top-notch security and authentication across various resources. While NTLMv2 represents an improvement over NTLM, Kerberos remains the gold standard for network authentication due to its advanced security features. Understanding the differences between these protocols is crucial for making informed decisions about network security and resource access in modern IT environments.