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Certificates

Couchbase Server supports x.509 certificates for client and server.

Certificates in Couchbase

Couchbase supports the use of x.509 certificates, for clients and servers. This ensures that:

  • Only approved users, applications, machines, and endpoints have access to system resources. For example, the mechanism can be used by Couchbase SDK clients, to access the Data, Query, and Search services; and by source clusters that use XDCR to replicate data to target clusters.

  • Clients can verify the identity of Couchbase Server, thereby ensuring that they are not exchanging data with a rogue entity.

Full Administrator and Security Administrator privileges are required, for the management of certificates.

Certificate Content

Certificate-based authentication relies on a Certificate Authority (CA), to validate identities and issue certificates. Each certificate includes information such as:

  • The name of the entity it identifies

  • An expiration date

  • The name of the CA that issued the certificate

  • The digital signature of the issuing CA

This information associates the identified entity with the issuing CA, such that third parties who know and trust the CA, but are unfamiliar with the identified entity, may elect to trust the identified entity on the basis of their trust in the CA. (Note that all systems that support use of certificates maintain a collection of trusted CA certificates, against which comparisons are made.)

Certificate Hierarchies

A single-tier certificate hierarchy is one where the CA has issued a certificate directly for the identified entity. If the receiving system trusts the CA, then the identified entity is trusted. The CA, since at the top of this two-element hierarchy, is referred to as the root CA.

An n-tier certificate hierarchy is one where a root CA has issued a certificate to an intermediate CA, who in turn has issued a certificate either to another intermediate CA, or directly to the identified entity. Use of an n-tier hierarchy requires that all intermediate certificates, as well as the entity’s certificate, be available for inspection; otherwise, clients will assume that the connection is not secure. This results in messages warning of an untrusted connection. All certificates should therefore be made available in a complete trust chain: which is a file that contains the entity’s certificates, concatenated with all intermediate certificates.

Server Certificates

Couchbase Server uses certificates to verify its identity in communications with clients. There are two kinds of server certificates used; which are the cluster certificate (for the entire cluster) and the node certificates (one for each node). These are described below.

Cluster Certificate

The cluster certificate is the public key of the root CA used by the cluster. Node certificates must be signed with the cluster certificate; otherwise, are warning is shown for each node during configuration. Unsigned nodes should be updated.

Node Certificate

Each contains the following:

  • The node private key

  • The node public key certificate file

  • The certificate chain-file, based on the supported CA hierarchy

Client Certificates

Client certificates allow a client to authenticate with a Couchbase Cluster. Each client certificate contains the authentication information (such as the username and password) appropriate for a certain level of resource-access.

When authenticating a client that uses x.509 certification, Couchbase Server asks the client to present the client certificate. If presented, the certificate’s time-validity is checked. If the certificate has not expired, credentials are read from it, and these are checked against registered users and their roles. If the user exists, and the associated roles are appropriate, access is granted; otherwise, access is denied.

Identity Encoding in Client Certificates

Different prefixes can be used within a client certificate, to identify the client. This is shown as follows:

"client_cert_auth": {
  "state": "enable",
  "prefixes": [
    {
      "path": "san.dnsname",
      "prefix": "www.",
      "delimiters": ".,;"
     },
     {},
     ...
  ]
}

The "prefixes" field is an array of {path, prefix, delimiters} tuples, where:

  • path can be one of the following values: "subject.cn", "san.uri", "san.email", "san.dns".

  • prefix specifies the client certificate prefix value.

  • delimiters is a list of characters that can individually be treated as a delimiter.

The following constraints apply when specifying multiple tuples:

  • A maximum of 10 {path, prefix,delimiters} tuples can be specified in the "prefixes" array.

  • No two tuples can have the same "path" and "prefix" fields.

  • All the fields in the tuple must be specified.

Client Certificate Enablement

Client-certificate handling is disabled by default, on Couchbase Server: it can optionally be enabled, and additionally if required, specified as mandatory. Couchbase Web Console, CLI, and REST API can all be used for this.

Requirements

Requirements for using X.509 certificates with Couchbase Server are as follows:

  • The certificate must be in .pem format.

  • The certificate must be an RSA key certificate.

  • The current system time must fall between the times set in the certificate-properties valid from and valid to.

  • The common name for the certificate must match the name of the host on which Couchbase Server is deployed, and can be any of the following (note that the subjectAltName can be used to define a certificate with multiple, alternative identities):

    • A nodename

    • An IP address

    • A URI (such as www.example.com)

    • A URL with a subject alternative name (SAN) certificate (such as example.com or example.net)

  • The node certificate must be designated for server authentication, by setting the optional field of the certificate’s property enhanced key usage to Server Authentication.

Best Practices

The following are recommended:

  • To avoid man-in-the-middle attacks, if the certificate’s common name is an IP address, do not use wildcards in the name.

  • Ensure that the RSA key-length is 2048 bits or higher, to ensure high security.

  • Ensure that the certificate-chain is completely valid - from the node certificate, through all intermediate certificates to the root certificate - by means of the OpenSSL Validate Certificate test.

List of Required Keys

The following table lists the keys required for server and client certificate-management:

Key name Description

Server-side files

ca.pem

Root CA public key or the cluster certificate.

int.pem

Intermediate public key. There can be one or more intermediate public keys in the hierarchy.

pkey.key

Node private key per node (private key of the node). Each node in the cluster must have its private key.

pkey.pem

Node public key (public key of the node). Each node in the cluster must have its public key.

chain.pem

Concatenated chain file (chain file). This file contains the node public key and the intermediate public keys that signed first the node key (pkey.pem) and then each other. This file does not contain the CA public key.

Client-side files

ca.pem

CA public key, which should be configured on the client

chain.pem

Concatenated chain file (chain file)