The Directory Server offers a number of mechanisms to secure access to sensitive data, such as access control rules to prevent unauthorized users from reading certain entries or attributes within entries and TLS to protect data from eavesdropping and tampering on untrusted networks. However, if a copy of the server's database files should fall into the hands of an unauthorized person, they could potentially extract sensitive information from those files. Because information in a database is stored in plain text, some sensitive information, such as government identification numbers or passwords, may not be protected enough by standard access control measures.
For highly sensitive information, this potential for information loss could present a significant security risk. In order to remove that security risk, Directory Server allows portions of its database to be encrypted. Once encrypted, the data are safe even in the event that an attacker has a copy of the server's database files.
Database encryption allows attributes to be encrypted in the database. Both encryption and the encryption cipher are configurable per attribute per back end. When configured, every instance of a particular attribute, even index data, is encrypted for every entry stored in that database.
An additional benefit of attribute encryption is, that encrypted values can only be sent to a clients with a Security Strength Factor (SSF) greater than 1.
There is one exception to encrypted data: any value which is used as the RDN for an entry is not encrypted within the entry DN. For example, if the
uid attribute is encrypted, the value is encrypted in the entry but is displayed in the DN:
# entry-id: 16
That would allow someone to discover the encrypted value.
Any attribute used within the entry DN cannot be effectively encrypted, since it will always be displayed in the DN. Be aware of what attributes are used to build the DN and design the attribute encryption model accordingly.
Indexed attributes may be encrypted, and attribute encryption is fully compatible with
pres indexing. The contents of the index files that are normally derived from attribute values are also encrypted to prevent an attacker from recovering part or all of the encrypted data from an analysis of the indexes.
Since the server pre-encrypts all index keys before looking up an index for an encrypted attribute, there is some effect on server performance for searches that make use of an encrypted index, but the effect is not serious enough that it is no longer worthwhile to use an index.
In order to use attribute encryption, the server must be configured for TLS and have TLS enabled because attribute encryption uses the server's TLS encryption key and the same PIN input methods as TLS. The PIN must either be entered manually upon server startup or a PIN file must be used.
Randomly generated symmetric cipher keys are used to encrypt and decrypt attribute data. A separate key is used for each configured cipher. These keys are wrapped using the public key from the server's TLS certificate, and the resulting wrapped key is stored within the server's configuration files. The effective strength of the attribute encryption is never higher than the strength of the server's TLS key used for wrapping. Without access to the server's private key, it is not possible to recover the symmetric keys from the wrapped copies.
There is no mechanism for recovering a lost key. Therefore, it is especially important to back up the server's certificate database safely. If the server's certificate were lost, it would not be possible to decrypt any encrypted data stored in its database.
If the TLS certificate is expiring and needs to be renewed, export the encrypted back end instance before the renewal. Update the certificate, then re-import the exported LDIF file.