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Database Laboratory
2013-10-21
TaeHoon Kim
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Database Laboratory
Regular Seminar
2013-10-21
TaeHoon Kim 3
Contents
1.
Introduction
2.
Security Overview
3.
Queries Over Encrypted Data
4.
Multiple Principals
5.
Application Case Studies
6.
Discussion
7.
Implementation
8.
Experimental Evaluation
9.
Related Work
10. Conclusion
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Introduction

Theft of private information is a significant problem


An adversary can exploit software vulnerabilities to gain
unauthorized access to servers
Curious or malicious admin at a hosting or application provider can
snoop on private data


One approach to reduce the damage is to encrypt sensitive data
This paper presents CryptDB

A system that explores an intermediate design point to provide
confidentiality for applications that use database management
systems
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5
Introduction

CryptDB addresses two threats


1. A curious database DBA who tries to learn private data
2. An adversary that gains complete control of application and
DBMS servers
Confidential Data Leaks
User 1
User 2
SQL
Application
DB Server
User 3

hackers
• cloud.berkeley.edu/data/cryptdb.pptx
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Introduction

CryptDB addresses these challenges using three key ideas

The first is to execute SQL queries over encrypted data



This idea using a SQL-aware encryption strategy
The second technique is adjustable query-based encryption
The third idea is to chain encryption keys to user passwords, so that
each data item in the database can be decrypted only through a
chain of keys rooted in the password of one of the users with
access to that data
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Security Overview

Threat1 : DBMS Server Compromise


Our approach is to allow the DBMS server to perform query
processing on encrypted data as it would on an unencrypted
database
Threat2 : Arbitrary Threats


The solution is to encrypt different data items (e.g., data
belonging to different users) with different keys
CryptDB provides strong guarantees in the face of arbitrary serverside compromises
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Security Overview(Threat1)
Application
SELECT * FROM emp WHE
RE salary = 100
table1 (emp)
Proxy
60
100
800
100
SELECT * FROM table1 WH col1/rank col2/name col3/salary
ERE col3 = x5a8c34
x934bc1
x95c623
x5a8c34
?
x5a8c34
x2ea887
x5a8c34
x2ea887
x84cec1
x4be219
x17cea7
x5a8c34
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Queries Over Encrypted Data

SQL-aware Encryption


Deterministic(DET)


Random(RND) : in indistinguishability under(IND-CPA)
Allows the server to perform equality check, which means it can
perform selects with equality predicates, equality joins, GROUP BY,
COUNT, DISTINCT
Order-preserving encryption(OPE)

OPE allows order relations between data items to be established
based on their encrypted values, without revealing the data itself

If x<y, then OPEk(X) < OPEk(Y), for any secret key K
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Queries Over Encrypted Data

Homomorphic encryption (HOM)


Join (Join and OPE-JOIN)



HOMk(x)*HOMk(y) = HOMk(x+y)
Join support all operations by DET,
OPE-JOIN support joins by order relations
Word Search (SEARCH)

Search is used to perform searches on encrypted text to support
operations such as MySQL’s LIKE operator

Only support full-word keyword searches
– Cannot support arbitrary regular expressions
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Queries Over Encrypted Data

Adjustable Query-based Encryption


Our goal is to use the most secure encryption schemes that enable
running the requested queries
Our idea is to encrypt each data item in one or more onions

Each value is dressed in layers of increasingly stronger encryption

To perform optimize adjustable query-based encryption
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Queries Over Encrypted Data

Executing Over Encrypted Data

The proxy transforms the query to operate on these onions


For instance, for the schema shown in Figure 3, a reference to the Name
column for an equality comparison will be replaced with a reference to
the C2-Eq column
Read Query Execution
1
2
3

Write Query Execution

The proxy encrypts each inserted column’s value with each onion layer
that has not yet been stripped off in that column
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Queries Over Encrypted Data

Improving Security and Performance

Minimum onion layers


Application developers can specify the lowest onion encryption
In-proxy processing

Since the proxy receives the entire result set from the server, sorting
these result in the proxy does not require significant amount of
computation, and does not increase the bandwidth requirements

Training mode

Onion re-encryption

When application performs infrequent queries requiring a low onion
layer, CryptDB could be extended to re-encrypt onions
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Queries Over Encrypted Data

Performance Optimization

Developer annotation


Known query set



If many column are not sensitive, the developer can instead provide
explicit annotation indicating the sensitive field
Use training mode
Optimize onion sets
Ciphertext pre-computing and caching

To reduce this cost, the proxy pre-computes and caches(for OPES)
encryptions of frequently used constants under different keys
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Multiple Principle: Policy Annotations

Policy Annotations



1. The developer must define the principal types(using PRINCTYPE)
used in her application, such as users, groups, or messages
2. The developer must specify which columns in her SQL schema
contain sensitive data, along with the principals that should have
access to data using the ENC_FOR annotation
3. Programmers can specify rules for how to delegate the privileges
of one principal to other principals, using the speak for relation
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Multiple Principle: Policy Annotations
Observation : Each row in certain tables naturally
specifies

1.
how data should be encrypted
privmsgs_to:
msgid
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6
privmsgs:
senderid recipientid
1
9
2
6
msgid
5
6
msgtext
“secret message”
“hello world”
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Multiple Principle: Policy Annotations
1. Principals
2. ENCRYPT_FOR
3. HAS_ACCESS_TO
Securing phpBB private messages:
PRINC TYPES physical_user EXTERNAL;
PRINC TYPES user, msg;
CREATE TABLE privmsgs (
msgid int,
subject varchar(255)ENCRYPT_FOR PRINC msgid TYPE msg,
msgtext text ENCRYPT_FOR PRINC msgid TYPE msg
);
CREATE TABLE privmsgs_to (
msgid int, rcpt id int, sender id int,
PRINC sender_id TYPE user HAS_ACCESS_TO PRINC msgid TYPE msg,
PRINC rcpt_id TYPE user HAS_ACCESS_TO PRINC msgid TYPE msg
);
CREATE TABLE users ( userid int,username varchar(255),
PRINC username TYPE physical_user HAS_ACCESS_TO PRINC userid TYPE user
);
• cloud.berkeley.edu/data/cryptdb.pptx
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Multiple Principle: Key chaining
userid 1
All key chaining operations
done at proxy, keys stored
encrypted at DB server
SKu1
Username: Alice
Password: asdf
ESKu1[SKm5]
msgid
5 SKm5
SKa = dblab
ESKa[SKu1]
“secret
messag
e”
SKm5
userid 2
Username: Tomas
Password: dfga
SKb = dblab
ESKb[SKu2]
SKu2
ESKu2[SKm5
]
• cloud.berkeley.edu/data/cryptdb.pptx
• Also use public key pair
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Application Study

PhpBB e.g)xpressEngine board


A widely used open source forum with a rich set of access control
settings
HotCRP


A popular conference review application
Grad-apply

A graduate admissions system used by MIT EECS
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Discussion / Implementation

CryptDB cannot support on encrypted Data

Not support both computation and comparison on the same column







SELECT age*2+10 FROM …
WHERE salary > age*2+10
(1)rewritten into a sub-query
(2)re-encrypted in the proxy
CryptDB proxy consist of a C++ Lib and a Lua module
CryptDB used MySQL proxy
CryptDB implementation consists of ~ 18,000 lines of C++ Code
and ~150 lines of Lua Code
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Performance Evaluation

Performance environment

MySQL 5.1.54 server : 2 machines



CryptDB proxy and the clients : 8 machines



2.4 GHz Intel Xeon E5620 4-core processors
12 GB of RAM
2.4 GHz AMD Opteron 8431 6-core processors
64 GB of RAM
Use a shared Gigabit Ethernet network

Use TPC-C query set

Compare with



MySQL
CryptDB
CryptDB with only Random encryption(RND) :strawman
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Performance Evaluation

Throughput of different types of SQL queries from the TPC-C
query
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Related work

Theoretical approaches ([Gentry’10], [Gennaro et al., ’10])


Search on encrypted data (e.g., [Song et al., ’00])


Restricted set of queries, inefficient
Systems proposals (e.g., [Hacigumus et al., ’02])]


Inefficient
Lower degree of security, rewrite the DBMS, client-side processing
Software checks (e.g., PQL, UrFlow, Resin)

No protection against adversaries with complete access to servers
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Conclusion

We presented CryptDB, a system that provides a practical and a
strong level of confidence in the face of two significant threats



1. A curious database DBA who tries to learn private data
2. An adversary that gains complete control of application and
DBMS servers
Our Evaluation show that CryptDB can support operations over
encrypted data
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
Note that,


All ppt contents is based on
“cloud.berkeley.edu/data/cryptdb.pptx” and paper by Christof
Kim(TaeHoon Kim) :D
If ppt contents contains error, plz recommend to me
[email protected] :D
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