An introduction to LDAP
Lightweight Directory Access Protocol (LDAP) is a standard protocol for accessing directory services. It enables search, modification, and authentication of data in distributed directory services 1. It is a message-oriented protocol, where clients and servers exchange a series of messages to perform directory operations. These operations fall into three main categories 1: Interrogation Operations: Allow clients to query the directory and retrieve data. The two primary interrogation operations are: Search: Search for specific directory entries based on criteria like attributes, values, or search filters. Compare: Test if a particular entry contains a specific attribute value. Update Operations: Enable clients to modify the directory’s contents. The update operations include: Add: Creating new directory entries with specified attributes and values. Delete: Removing existing entries from the directory. Modify: Changing attribute values or adding/removing attributes from existing entries. Rename / Modify Distinguished Name: Renaming or moving entries within the directory’s hierarchical structure. Authentication and Control Operations: Manage client connections and security. They include: Bind: Clients authenticate themselves to the server using a Distinguished Name (DN) and credentials, typically a password or digital certificate. Unbind: Clients terminate their session with the server Abandon: Clients indicate they are no longer interested in the results of a previously submitted operation. LDAP supports various authentication methods to verify a client’s identity. In the easiest scenario, the client provides it’s DN and password in clear text to the server for verification (e.g., SSO with login credentials 2). This approach is called Simple Bind. While straightforward and easy to implement, it is inherently insecure if used without encryption, as the credentials can be intercepted by eavesdroppers. To mitigate this risk, Simple Bind should always be used in conjunction with encryption protocols such as TLS 1. The Simple Authentication and Security Layer (SASL) framework, introduced in LDAPv3, enables more secure and flexible authentication mechanisms and binds the LDAP server to a protocol like Kerberos 2 1. Common SASL mechanisms include DIGEST-MD5, which protects passwords by transmitting them as a cryptographic hash instead of plaintext, thus safeguarding against eavesdropping. Additionally, SASL allows negotiation of lower-layer security features, such as encryption of all subsequent client-server communications, ensuring enhanced data protection 1. LDAP’s security model is built upon the concept of connection-oriented communication and authentication. Once a client authenticates (binds) to the server, it is granted privileges based on its identity and the server’s access control policies. These policies define what actions the client is permitted to perform on specific directory entries or attributes. LDAP servers typically provide access control models that allow granular control over data access, enabling administrators to define fine-grained permissions for different users and groups 1. T. Howes, M. Smith, and G. S. Good, Understanding and Deploying LDAP Directory Services. Addison-Wesley Professional, 2003. Online ↩ Red Hat, Inc., "What is lightweight directory access protocol (LDAP) authentication?" Online ↩
Lightweight Directory Access Protocol (LDAP) is a standard protocol for accessing directory services. It enables search, modification, and authentication of data in distributed directory services 1. It is a message-oriented protocol, where clients and servers exchange a series of messages to perform directory operations. These operations fall into three main categories 1:
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Interrogation Operations: Allow clients to query the directory and retrieve data. The two primary interrogation operations are:
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Search: Search for specific directory entries based on criteria like attributes, values, or search filters. -
Compare: Test if a particular entry contains a specific attribute value.
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Update Operations: Enable clients to modify the directory’s contents. The update operations include:
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Add: Creating new directory entries with specified attributes and values. -
Delete: Removing existing entries from the directory. -
Modify: Changing attribute values or adding/removing attributes from existing entries. -
Rename/Modify Distinguished Name: Renaming or moving entries within the directory’s hierarchical structure.
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Authentication and Control Operations: Manage client connections and security. They include:
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Bind: Clients authenticate themselves to the server using a Distinguished Name (DN) and credentials, typically a password or digital certificate. -
Unbind: Clients terminate their session with the server -
Abandon: Clients indicate they are no longer interested in the results of a previously submitted operation.
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LDAP supports various authentication methods to verify a client’s identity. In the easiest scenario, the client provides it’s DN and password in clear text to the server for verification (e.g., SSO with login credentials 2). This approach is called Simple Bind. While straightforward and easy to implement, it is inherently insecure if used without encryption, as the credentials can be intercepted by eavesdroppers. To mitigate this risk, Simple Bind should always be used in conjunction with encryption protocols such as TLS 1.
The Simple Authentication and Security Layer (SASL) framework, introduced in LDAPv3, enables more secure and flexible authentication mechanisms and binds the LDAP server to a protocol like Kerberos 2 1. Common SASL mechanisms include DIGEST-MD5, which protects passwords by transmitting them as a cryptographic hash instead of plaintext, thus safeguarding against eavesdropping. Additionally, SASL allows negotiation of lower-layer security features, such as encryption of all subsequent client-server communications, ensuring enhanced data protection 1.
LDAP’s security model is built upon the concept of connection-oriented communication and authentication. Once a client authenticates (binds) to the server, it is granted privileges based on its identity and the server’s access control policies. These policies define what actions the client is permitted to perform on specific directory entries or attributes. LDAP servers typically provide access control models that allow granular control over data access, enabling administrators to define fine-grained permissions for different users and groups 1.
