Hierarchical Key Applications for Assured Destruction of Deleted Material

The Big Issue Alice has a remotely backed-up filesystem Files are encrypted on the remote server One day, Alice decides she wants to delete /var/secrets /var /var/www /var/secrets 2

The Big Issue However, Alice may not be able to guarantee deletion from the remote server The backup service may queue deletions for later… /var /var/www /var/.secrets 3

The Big Issue …and/or incremental backups of the deleted directory may still exist It may be important that no copy of the data exists at all. 2011/var 2011/var/www 2011/var/secrets 2010/var 2010/var/www 2010/var/secrets 4

A Similar Issue ‘Vanish’ [Geambasu – Security 2009] proposed Self-Destructing Data Bits of keys are distributed over public or semi- public DHTs via Shamir’s Secret Sharing Eventually enough parts of the key are lost due to churn and node self-cleansing that the data is not recoverable 5

A Similar Issue Vanish destroys data with some probability, increasing over time Sometimes “high probability” is not good enough 6

Goals Confidentiality Assurance of Irrecoverability High, consistent granularity Simplicity of deletion of sub-grain blocks of data Low overhead 7

Attribute Based Encryption Sahai and Waters’ 2004 paper “Fuzzy Identity- Based Encryption” introduced Attribute-Based Encryption In an ABE system, each ciphertext is accompanied by a list of attributes Keys can be constructed such that they will only decipher data with certain accompanying attributes 8

Attribute Based Encryption {Billing Dept., Security Clearance, Company Health Plan} {Security Clearance, Billing Dept., Human Resources} 9

Attribute Based Encryption {Billing Dept., Security Clearance, Company Health Plan} {Security Clearance, Billing Dept., Human Resources} 10

Project Proposal {/var, */foo, *.txt} {/var, */www, */foo *.txt} 11 {/var, */www */secrets, *.mkv, *.nzb} {/bin, */zap, */rows, *.dower,}

Project Proposal {/var, */secrets, *.nzb} {/var, */www, */foo *.txt} 12 {/var, */www */secrets, *.mkv, *.nzb} {/bin, */zap, */rows, *.dower,}

Our Solution {/var, */secrets, *.nzb} {/var, */www, */foo *.txt} 13 {/var, */www */secrets, *.mkv, *.nzb} {/bin, */zap, */rows, *.dower,}

Issues to Explore Granularity ▫The higher the granularity (i.e. the more precise deletions that are made possible) the larger the keyset must be Hierarchical structure ▫There's probably some clever trickery where we can shape the keys to be hierarchical - i.e., as is the filesystem ▫We believe the aforementioned adaptation of ABE can accomplish this efficiently 14

Proposal Summary Project Objectives: ▫Hierarchy-based, adjustable granularity adaptation of attribute-based encryption ▫Ability to efficiently delete sub-block-size chunks of data Requirements: ▫4 months ▫$33,000 15