limiting liability in a federally compliant file system
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Limiting Liability in a Federally Compliant File System. Zachary N. J. Peterson Randal Burns Adam Stubblefield. Overview. Recent legislation makes new requirements with respect to the management of electronic records How does one electronically “leave the past behind?” - PowerPoint PPT PresentationTRANSCRIPT
Department of Computer Science, Johns Hopkins University
Limiting Liability in a Federally Compliant File System
Zachary N. J. PetersonRandal Burns
Adam Stubblefield
PORTIA Workshop 2004
Overview Recent legislation makes new requirements with
respect to the management of electronic records How does one electronically “leave the past behind?”
– Data managers may wish to limit their liability– Patients/account holders may wish for their data to expire
We have developed a method for securely deleting data in a regulatory environment
– Fast & efficient– No additional key overhead
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A Paperless World Information records are becoming entirely electronic
– Financial records, medical records, federal data– 300 million computers storing 150,000 terabytes of data
Eases use, sharing, and indexing Allows for undetectable modification, eaves-dropping,
and other more devious things Congress and others have begun to address the
importance of managing and securing electronic records
Over 4,000 federal, state and local laws and regulations with regard to electronic record management
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The Law and Storage Health Insurance
Portability and Accountability Act (HIPAA) (1996)
Government Information Security Reform Act (GISRA)
Federal Information Security Management Act (FISMA) (2002)
E-SIGN (2000) Sarbanes-Oxley (2002) Gramm-Leach-Bliley
(2002) USA-PATRIOT Act Federal Records Act DoD Directive 5015.2 And on and on…
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Distilling Regulatory Requirements Authentication and Authorization Audit Trail
– Files should be versioned over time– Secure block sharing between versions
Secure Storage and TransmissionThe use of cryptography for:– Privacy and confidentiality– Non-repudiation
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Secure Deletion in the Regulatory Environment Organizations must take steps to protect privacy Desire to limit liability
– Records that go out of audit scope should do so forever – Patients may wish to redact portions of their medial record
When a disk is subpoenaed, old and irrelevant data should be inaccessible
Simply “emptying the trash” isn’t good enough– Only frees the blocks for future allocations– Even after reuse, overwritten data may be reconstructed
using magnetic force microscopy
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Existing Techniques Secure Overwrite [Gutmann 96]
– Data blocks are overwritten many times with alternating patterns of 1s and 0s
– Magnetic media is degaussed and safe from MFM Key Disposal [Boneh & Lipton 96]
– Data encrypted with a key– Key is securely deleted, eliminating meaningful data access
User Space Tools– CyberScrub– Overwrite– Wipe
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Technical Problems Secure overwriting of noncontiguous data blocks is
slow and inefficient– When versions share blocks, data to be overwritten may be
noncontiguous Cannot dispose file keys in a versioning file system
– Blocks encrypted with a particular key need to be available in future versions
User space tools are categorically inadequate– Can’t delete metadata– Can’t be interposed between file operations– Truncate may leak data– Synchronicity is difficult and inconvenient
PORTIA Workshop 2004
The Big Idea
A keyed all-or-nothing transform takes a key, a data block, and a nonce
Encryption creates an encrypted block and a stub When the key is private, data is secure and
authenticated Securely deleting stub, securely deletes block, even
if the key is later exposed
iiik sCNBf ||),( →
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All-or-nothing (AON) Encryption[Boyko 99] [Rivest 96]
A mode for block ciphers that requires all cipher blocks to be decrypted before the message block is recovered
Increases the searchable key space for brute-force attacks
– Attacker slowed down by a factor equal to the number of blocks in the cipher text
By definition, destroying any cipher block destroys the entire message block
Our work is the first practical application of AON
PORTIA Workshop 2004
Features of our System Stub length is a security parameter
– In practice, the stub might be 128 bits Stubs are stored with metadata and are not secret When deleting a version, metadata and stubs are
securely overwritten– this securely removes all data for that version
Stubs of the shared blocks are replicated to new versions
– Shared data are preserved when previous versions are deleted
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C0
Example
C1 C2
s0 s1 s211 …
Disk
File Metadata
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17 …
C0
Example
C1 C2
s0 s1 s211 …
Disk
File Metadata
s0 s1 s2
Receive a write to block #2 at time 17
C1’
s1’
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C0
Example
C1 C2 C1’
s0 s1 s211 …
Disk
s0 s1’ s217 …
File Metadata
Delete file at time 11
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C0
Example
C1 C2 C1’
s0 s1 s211 …
Disk
s0 s1’ s217 …
File Metadata
Delete file at time 11
Block C1 is deleted permanently
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More Features No extra key overhead added to the system when
compared with other secure systems– Versions of a file may use the same key for encryption
AON encryption allows the deletion of any 128 bits– Instead of removing the stub, 128 bits of the block may be
securely overwritten instead– More efficient when removing data from all versions of a file
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C0
Example
C1 C2
s0 s1 s211 …
Disk
File Metadata
s0 s1 s217 ……
PORTIA Workshop 2004
C0
Example
C1 C2
s0 s1 s211 …
Disk
File Metadata
s0 s1 s217 ……
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Availability Implementing this secure deletion scheme in
ext3cow– A fully working snapshot file system for the Linux
2.4 kernel Web site: www.ext3cow.com
– Download the patch– Read the technical report– Join the mailing list
Email: [email protected]
PORTIA Workshop 2004
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Electronic Record Legislation HIPAA (1996)
– Technical security mechanisms
– Physical safeguards E-SIGN (2000)
– Digital contracts are as legitimate as paper contracts
FISMA (2002)– Framework for ensuring
security controls for storage– Security of system must be
commensurate with security of data
Sarbanes-Oxley (2002)– CEO, CFO responsible for
accurate financial reports– Management assessment of
internal controls– Real time disclosure– Criminal penalties for altering
documents Gramm-Leach-Bliley (2002)
– Consumer records kept confidential
– Protect against threats and unauthorized access
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The Law and Storage Health Insurance
Portability and Accountability Act (HIPAA)
Government Information Security Reform Act (GISRA)
Federal Information Security Management Act (FISMA)
Sarbanes-Oxley (SOX) Gramm-Leach-Bliley
(GLB) PATRIOT Act Federal Records Act DoD Directive 5015.2 4,000+ State and
Federal Laws and Regulations with regard to storage
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What are the requirements? Authorization
– Access controls (role-based authorizations)
– Encryption (confidentiality)
– Digital signatures (non-repudiation)
Authentication
Audit Trail– Record of all changes
Secure Storage and Transmission
– More encryption? Integrity & Reliability
– Unaltered records.– Trusted content.
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Introducing Ext3cow A file system based on ext3 that supports file
system snapshot with a time-shifting interface.– Creates immutable views of a file system as it
appeared at a specific point in time.– Versions of a file are created with copy-on-write
(cow) of blocks.– Snapshots are addressed with an
epoch number that corresponds to a system time (gettimeofday).
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Securing our COW file system Challenges
– How to encrypt files that share blocks between versions.
– How to change permissions such that a user who had access to a file in the past is not able to access current versions.
– Securely deleting files such that they are no longer able to be subpoenaed.
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Conclusions New legislation requires versioning, security
and privacy– Versioning must be fast?
AON encryption allows for secure deletion with minimal secure overwriting– More efficient than securely overwriting
noncontiguous data blocks– Does not increase key overhead