Users trust Accumulo to properly enforce access control over their data, as specified by the visibility field. This trust can be broken by a malicious administrator or malfunctioning server, revealing sensitive information to unauthorized individuals. Our prior work encrypts data in Accumulo to protect its confidentiality from a malicious server, but does not protect against this attack. To address this threat, we have implemented a client-side tool that cryptographically enforces visibility labels in Accumulo. Our solution is called Cryptographically Enforced Attribute-Based Access Control (CEABAC), and consists of two components: an encryption protocol and a key management system. CEABAC generates a fresh encryption key for each, then encrypts this key based on the cell’s visibility field. To accomplish this, the user must be able to create, store, retrieve, and revoke keys associated with each attribute that can appear in the system. The protocol guarantees that, if keys are distributed appropriately, a client without the appropriate permissions to view a cell cannot decrypt it, even if they receive its ciphertext. In the talk we will discuss the CEABAC protocol, our key management solution, how we implemented it in Accumulo, and future directions for this work. – Speaker –  Dr. Scott Ruoti Technical Staff, MIT Lincoln Laboratory Scott Ruoti is a researcher at MIT Lincoln Laboratory. He graduated from Brigham Young University in 2016 with a Ph.D. in computer science, focusing on security and HCI. Recently, he has been working on cryptographic enforcement of access control in Accumulo. — More Information — For more information see http://www.accumulosummit.com/

1. Cryptographically Securing Accumulo
Scott Ruoti
Robert K. Cunningham, Emily Shen,
Cassandra Sparks, Leo St. Amour
October 11, 2016
DISTRIBUTION STATEMENT A. Approved for public release: distribution unlimited.
This material is based upon work supported by the Department of Defense under Air Force Contract
No. FA8721-05-C-0002 and/or FA8702-15-D-0001. Any opinions, findings, conclusions or
recommendations expressed in this material are those of the author(s) and do not necessarily reflect
the views of the Department of Defense.
© 2016 Massachusetts Institute of Technology.
Delivered to the U.S. Government with Unlimited Rights, as defined in DFARS Part 252.227-7013 or
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defined by DFARS 252.227-7013 or DFARS 252.227-7014 as detailed above. Use of this work other
than as specifically authorized by the U.S. Government may violate any copyrights that exist in this
work.

2. Accumulo Summit 2016 - CEABAC - 2
SIR 10/11/16 Malicious Administrator
Querying
Clients
Threats to Accumulo
Network
Data
Sources
System Administrator
Threat 1: Malicious clients
Threat 2: External attacker Threat 3: Malicious cloud or admins
• Make unauthorized queries
• Learn stored data
• Learn other clients’ queries
• Insert malware
• Hack or compromise
system
• Learn contents of data & queries
• Modify, forge, or delete data
• Misattribute data to honest clients
Our focus: security against a malicious cloud or system administrators

3. Accumulo Summit 2016 - CEABAC - 3
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Existing Safe Guards
Querying
Clients
Network
Data
Sources
Data in motion
encryption
Accumulo provides
no safeguards!
Data at rest encryption
Malicious Administrator

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Our Work
Querying
Clients
Network
Data
Sources
Digital
signatures
Field-level
encryption
Verifiable
query results
Our approach: cryptographically securing against malicious insiders
Cryptographically
enforced access control
Malicious Administrator

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Project Status
• Implementation nearing completion
• Releasing soon
– Drop-in compatibility with Accumulo
• Goal: to obtain community feedback and involvement

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Outline
• Overview
• Securing Accumulo
– Field-level encryption
– CEABAC
– Key infrastructure
• “How can I use it?”
• Wrap-up

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Field-level Encryption
• Problem: administrator can read the data stored in Accumulo
• Solution: encrypt the data stored in Accumulo
– Only clients with the appropriate keys can read the data

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• Entries in Accumulo are broken up into multiple fields
Accumulo Entries
Key Value
Row Column Visibility
Permit equality and
range queries, likely
to be sensitive
Used by server for
access control
Unstructured,
likely to be
sensitive
Value

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Encryption Techniques
No Encryption
Deterministic
Encryption
Semantically
Secure
Encryption
Security No security guarantees
Limited confidentiality
May leak information
about the plaintext
Confidentiality
Query
Performance
Results can be filtered
server-side
Limited server-side
filtering of results
Client must retrieve all
rows and filter locally
DET Sem

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• Allow developers to configure how to encrypt each field
• Example: sensitive row, column, and value
– Deterministic encryption on the row and column for targeted keyword search
– Authenticated encryption on the value
Row Column Visibility Value
Patient 1 diagnosis doctor …
Configurable Encryption
DET SemDET

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• Problem: malicious administrator can incorrectly enforce visibility constraints
• Solution: encrypt fields based on the visibility expression
– Only clients with appropriate attributes can read the data
Patient 1, diagnosis?
Access Control
Row Column Visibility Value
Patient 1 Diagnosis
(Nurse&
ER)|Doctor
…
Doctor
Diagnosis data
Patient 1, diagnosis?
No results
Patient 1, diagnosis?
Diagnosis data
Clerk

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Cryptographically Enforced
Attribute-Based Access Control (CEABAC)
Row Column Visibility Value
Patient 1 Diagnosis
(Nurse&ER)
|Doctor
OR
Doctor
Nurse ER
AND
Field Key
Attribute Keys
Row Column Visibility Value
Patient 1 Diagnosis
(Nurse&ER)|Doct
or
…
Additional storage linear
in size of visibility field

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Key Management
• Generation
– Field-level encryption keys
– CEABAC attribute keys
• Distribution
– Ensure only correct individuals have access to keys
• Revocation
– Remove access to data encrypted after the revocation

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Key Management Life Cycle
User Information Key
Generation
Step 1: generate keys for a
given user
Key
Storage
Step 2: wrap keys with
users’public keys and
insert them into a
trusted key store
ClientsAPI
Step 3: clients
fetch their keys
from the store as
needed
Step 4: when a key is
revoked, generate a
new version and add
it to the key store

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Outline
• Overview
• Securing Accumulo
• “How can I use it?”
• Wrap-up

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Java Library
• Accumulo 1.8
• EncryptedBatchWriter
– Drop-in replacement for BatchWriter
• EncryptedBatchScanner
– Drop-in replacement for BatchScanner
– Support server-side filtering
• EntryEncryptorConfiguration and FieldEncryptorConfiguration
– Comes with example configurations
– Configurable using INI files

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Example
Code
EncryptionKeyContainer keys = ...;
BatchWriterConfig bwConfig = ... ;
EncryptionConfig config = EncryptionConfig.read(new FileReader("config.ini"));
EncryptedBatchWriter writer = new EncryptedBatchWriter(conn, "medical", bwConfig, config, keys);
Mutation mutation = new Mutation(new Text("medical"));
mutation.put(new Text("Patient 1"), new Text("diagnosis"),
new ColumnVisibility("doctor"), diagnosisBytes);
writer.add(mutation);
writer.close();
Config
[row]
algorithm = AES_DET_CBC
key_id = row_key
key_length = 256
sources = row
[colFamily]
algorithm = AES_DET_CBC
key_id = col_key
sources = colFamily, colQualifier
[value]
algorithm = AES_GCM
sources = value

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Key Infrastructure
• EncryptKeyContainer
– Interface
• We will provide reference implementation and key server
– Use it, modify it, roll your own
– Should be run on a trusted system

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Availability
• In the process of getting this work open sourced
• Python prototype library
– Most of the features from the Java library
– Coming soon
• Java library
– 2017
– Comes with examples
• Reference key server
– 2017

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Outline
• Overview
• Securing Accumulo
• “How can I use it?”
• Wrap-up

21. Accumulo Summit 2016 - CEABAC - 21
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• Field-level encryption
– Deterministic encryption must be used
with caution
• CEABAC
– Encrypted data cannot be filtered server
side (e.g., ScannerBase.setRanges)
– Encrypting user must have all the
attributes that make up the visibility
expression
– Susceptible to collusion
Limitations
A B
AND
A B

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Future Work
• Integrate with other work on cryptographically securing Accumulo
– Integrity of data (signatures)
– Completeness of query results (authenticated data structures)
• Optimizations
– Increase the speed of field-level encryption and CEABAC
– Reduce storage overhead for CEABAC
– Reduce storage overhead of the key server
• New features
– Cryptographically enforce query policies
– Alternative methods for enforcing visibility

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Participation from the Community
• Open source project
– New features
– Optimizations
– Maintenance
• Implemented inside of Accumulo code base
– More elegant
– Higher performance

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Conclusion
• Protects Accumulo from a malicious or compromised server
– Field-level encryption
– Cryptographically Enforced Attribute-Based Access Control (CEABAC)
• We want to start building community engagement
– Contact pace-contact@ll.mit.edu to be notified when the code is open-sourced
Questions?