pVault Sharing Architecture Ravi Chandra Jammalamadaka

pVault: Secure Personal Data Manager Users use the same passwords across different sites including secure and insecure sites which cannot be trusted . As a result same password attacks become common. Only solution is to remember a strong password for every website that requires password authentication. How many strong passwords can we remember ??

pVault features Stores passwords securely in a remote location. Generates strong passwords during registration. Provides mobile access of passwords. Autofills the required password on the website visited. Prevents Pharming and Phishing attacks

Download pVault pVault websites: http://www.itr-rescue.org/pVault http://www.responsphere.org/pVault

pVault Entry Based on XML All pvault entries are XML documents which follow a particular schema. Stores personal data (secrets) that belongs to more than one URL.

pVault Entry schema * pVault_Entry Secret Metadata Actualdata Individual_Secret url Name id Keywords

Design Criteria Store pvault entries in a relational database at the server (i.e. No changes at the server). Minimal Client side software and data storage. Allow both group sharing and sharing with individuals. PKI based

Security Consideration Data confidentiality: Protecting data from being accessed from unauthorized users. Data Integrity: Prevent tampering of the data at the server side.

Privacy Policy Rule Syntax: <object> < subject> <Access Modes> Group id/User Id Leaf node in the pvault entry Read/Write Example: \\pvault_entry Ravi read

XML subtree encryption pVault_Entry * Secret Metadata Actualdata url Keywords Encrypted_Node id Name Individual_Secret

Structure Preserving encryption pVault_Entry * * Secret url * E(Id) Metadata E(Name) E(Actualdata) Individual_Secret * E(keywords) E(Metadata) E(Actualdata)

Issues There is no requirement to hide the structure of the pvault entry from the server. ( public knowledge) Just Encrypt the content of the leaf nodes, structure preserving. Allows queries to be run at the server side.

Creating a Pvault Entry E (PE) E ( K ) K P A E ( K ) P E ( PE) A K Server PE K User A

Reading a Pvault Entry E (PE) K E (PE) K E (K) P A E (K) P A User A

Writing a pVault Entry Execute the read protocol Update the PE Replace the previous PE.

Sharing Protocol E (PE) K E ( PE) E (PE) K K E ( K) E ( K) E ( K) P B E ( K) E ( K) E ( K) P E ( K) P P B P A A B E ( K) Server P B PE K K PE User A User B

Data Integrity Since the Data is Stored at an Untrusted site, the service provider can 1. Modify data objects 2. Delete data objects 3. Not send the correct query results How do we prevent the Service Provider from doing above ??

XML Integrity 1 2 3 4 5 6 7 h( h(1.tag) || h(2) || h(5)) h(3.value + 3.tag) h(h(2.tag)|| h(3) || h(4)) h( h(1.tag) || h(2) || h(5)) h(4.value + 4.tag) h(6.value + 6.tag) h(7.value + 7.tag) h(h(5.tag)|| h(6) || h(7))

Another Method * * * pVault_Entry urlcount secretcount Secret id Metadata Name Actualdata Individual_Secret * metadatacount Keywords Metadata Actualdata

Drawbacks How is access to a pvault entry revoked ? Re-encrypt the pvault and update the key entries for other users. Similar deal when a user leaves a group. Re-encryption Inevitable. Burden for the client.

Using Server as a Certificate Authority Since the server is untrusted, the server can lie about the public key. When Alice wants to share a file with Bob, Alice requests the public key from the server. The server can generate a new public key/private key pair and return the public key as Bob’s public key. The sever now has access to all the files that Alice shares with Bob.

Secure Coprocessor SC is a general purpose computer that can be trusted faithfully to perform a computation. SC are resistant against forseeable physical and logical attacks, except DOS attacks. Trusted Third Party IBM 4758 SC is equipped with 99Mhz and 2 MB onboard memory.

Secure Coprocessor Duties Provide access to private keys of pvault users. During revocation, re-encrypt pvault entries.

Lost Update Problem Client/User requests an update on pvault entry o to change its content from c to c . The server ignores the update. The next time the pvault entry o is queried the server return c as the pvault entry’s content. How can the client be sure about the freshness of the pvault entry’s content?? - Maintain Version numbers.