HDFS Transparent Encryption

HDFS Encryption implements transparent, end-to-end encryption of data read from and written to HDFS, without requiring changes to application code. Because the encryption is end-to-end, data can be encrypted and decrypted only by the client. HDFS does not store or have access to unencrypted data or encryption keys. This supports both at-rest encryption (data on persistent media, such as a disk) and in-transit encryption (data traveling over a network).

Use Cases

Data encryption is required by a number of different government, financial, and regulatory entities. For example, the healthcare industry has HIPAA regulations, the card payment industry has PCI DSS regulations, and the United States government has FISMA regulations. Transparent encryption in HDFS makes it easier for organizations to comply with these regulations. Encryption can also be performed at the application-level, but by integrating it into HDFS, existing applications can operate on encrypted data without changes. This integrated architecture implements stronger encrypted file semantics and better coordination with other HDFS functions.


Encryption Zones

An encryption zone is a directory in HDFS with all of its contents encrypted, that is, every file and subdirectory in it is encrypted. The files in this directory will be transparently encrypted upon write and transparently decrypted upon read. Each encryption zone is associated with a key, which is specified when the zone is created. Each file within an encryption zone also has its own encryption/decryption key, called the Data Encryption Key (DEK). These DEKs are never stored persistently unless they are encrypted with the encryption zone's key. This encrypted DEK is known as the EDEK. The EDEK is then stored persistently as part of the file's metadata on the NameNode.

A key can have multiple key versions, where each key version has its own distinct key material (that is, the portion of the key used during encryption and decryption). Key rotation is achieved by modifying the encryption zone's key, that is, bumping up its version. Per-file key rotation is then achieved by re-encrypting the file's DEK with the new encryption zone key to create new EDEKs. An encryption key can be fetched either by its key name, returning the latest version of the key, or by a specific key version.

Key Management Server

A new service, called the Hadoop Key Management Server (KMS), needs to be added to your cluster to store, manage, and access encryption keys. The KMS service is a proxy that interfaces with a backing key store on behalf of HDFS daemons and clients. Both the backing key store and the KMS implement the Hadoop KeyProvider client API.

Encryption and decryption of EDEKs happens entirely on the KMS. More importantly, the client requesting creation or decryption of an EDEK never handles the EDEK's encryption key (that is, the encryption zone key). When a new file is created in an encryption zone, the NameNode asks the KMS to generate a new EDEK encrypted with the encryption zone's key. When reading a file from an encryption zone, the NameNode provides the client with the file's EDEK and the encryption zone key version that was used to encrypt the EDEK. The client then asks the KMS to decrypt the EDEK, which involves checking that the client has permission to access the encryption zone key version. Assuming that is successful, the client uses the DEK to decrypt the file's contents. All the steps for read and write take place automatically through interactions between the DFSClient, the NameNode, and the KMS.

Access to encrypted file data and metadata is controlled by normal HDFS filesystem permissions. Typically, the backing key store is configured to only allow end-user access to the encryption zone keys used to encrypt DEKs. This means that EDEKs can be safely stored and handled by HDFS, since the hdfs user will not have access to EDEK encryption keys. This means that if HDFS is compromised (for example, by gaining unauthorized access to a superuser account), a malicious user only gains access to the ciphertext and EDEKs. This does not pose a security threat since access to encryption zone keys is controlled by a separate set of permissions on the KMS and key store.

For more information about configuring the KMS, see Configuring the Key Management Server (KMS).

Navigator Key Trustee

HDFS encryption can use a local Java KeyStore for key management. This is not sufficient for production environments where a more robust and secure key management solution is required. Cloudera Navigator Key Trustee Server is a key store for managing encryption keys and other secure deposits.

In order to leverage the manageable, highly-available key management capabilities of the Navigator Key Trustee Server, Cloudera provides a custom KMS service, the Key Trustee KMS.

For more information, see Enabling HDFS Encryption Using the Wizard.

DistCp Considerations

A common use case for DistCp is to replicate data between clusters for backup and disaster recovery purposes. This is typically performed by the cluster administrator, who is an HDFS superuser. To retain this workflow when using HDFS encryption, a new virtual path prefix has been introduced, /.reserved/raw/, that gives superusers direct access to the underlying block data in the filesystem. This allows superusers to distcp data without requiring access to encryption keys, and avoids the overhead of decrypting and re-encrypting data. It also means the source and destination data will be byte-for-byte identical, which would not have been true if the data was being re-encrypted with a new EDEK.

Copying between encrypted and unencrypted locations

By default, distcp compares checksums provided by the filesystem to verify that data was successfully copied to the destination. When copying between an unencrypted and encrypted location, the filesystem checksums will not match since the underlying block data is different.

In this case, you can specify the -skipcrccheck and -update flags to avoid verifying checksums.

Attack Vectors

Type of Exploit Issue Mitigation
Hardware Access Exploit

These exploits assume the attacker has gained physical access to hard drives from cluster machines, that is, DataNodes and NameNodes.

Access to swap files of processes containing DEKs. This exploit does not expose cleartext, as it also requires access to encrypted block files. It can be mitigated by disabling swap, using encrypted swap, or using mlock to prevent keys from being swapped out.
Access to encrypted block files. This exploit does not expose cleartext, as it also requires access to the DEKs. It can only be mitigated by restricting physical access to the cluster machines.
Root Access Exploits

These exploits assume the attacker has gained root shell access to cluster machines running DataNodes and NameNodes. Many of these exploits cannot be addressed in HDFS, since a malicious root user has access to the in-memory state of processes holding encryption keys and cleartext. For these exploits, the only mitigation technique is carefully restricting and monitoring root shell access.

Access to encrypted block files.

By itself, this does not expose cleartext, as it also requires access to encryption keys.

No mitigation required.
Dump memory of client processes to obtain DEKs, delegation tokens, cleartext.

No mitigation.

Recording network traffic to sniff encryption keys and encrypted data in transit.

By itself, insufficient to read cleartext without the EDEK encryption key.

No mitigation required.
Dump memory of DataNode process to obtain encrypted block data.

By itself, insufficient to read cleartext without the DEK.

No mitigation required.
Dump memory of NameNode process to obtain encrypted data encryption keys.

By itself, insufficient to read cleartext without the EDEK's encryption key and encrypted block files.

No mitigation required.
HDFS Admin Exploits

These exploits assume that the attacker has compromised HDFS, but does not have root or hdfs user shell access.

Access to encrypted block files.

By itself, insufficient to read cleartext without the EDEK and EDEK encryption key.

No mitigation required.
Access to encryption zone and encrypted file metadata (including encrypted data encryption keys), using -fetchImage.

By itself, insufficient to read cleartext without EDEK encryption keys.

No mitigation required.
Root Access Exploits
  A rogue user can collect keys to which they have access, and use them later to decrypt encrypted data. This can be mitigated through periodic key rolling policies.