Hierarchical Key Applications for Assured Destruction of Deleted Material

1. Hierarchical Key Applications for Assured Destruction of Deleted Material

2. 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

3. 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

4. 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

5. 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

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

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

8. 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

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

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

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

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

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

14. 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

15. 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