PORSCHA PORSCHA : POLICY ORIENTED SECURE CONTENT HANDLING IN ANDROID Machigar Ongtang, Kevin Butler, Patrick McDaniel Dhurakij Pundit University, University of Oregon, Pennsylvania State University ACSAC(2010)
Agenda Introduction Content on Smart Phone About Android Architecture Evaluation Discussion Conclusion
Android provide few direct protections for the content placed on the phone DRM(Digital Right Management) DRM(Digital Right Management) Porscha: content should only be accessible by explicitly authorized phones content should only be accessed by provider endorsed applications content should be subject to contextual constraints Two phases of Porscha: in transit on platform Introduction
Content on Smart Phone Personal and Business Documents Service-specific data spy camera Mydroid Financial Information
Content on Smart Phone DRM Policy Requirements Binding content to the phone Binding content to endorsed applications Constraining continuing use of the content
About Android Four types of components Two groups of applications Documents in transit & on-platform access
About Android On-platform access Initial Document Recipients Documents at Rest Document Sharing
Architecture Constraints on Devices - binding to specific devices identified by the users' International Mobile Subscriber Identity (IMSI) or WAP Identify Module (WIM).International Mobile Subscriber Identity (IMSI) Constraints on Applications - be restricted to applications with a given code fingerprint (hash of the application image) Constraints on Use - support not only the regulation of simple accesses, but also differentiation of simple access from read, modify and delete rights
Architecture - in transit Identity-Based Encryption (IBE):enables the senders to construct the public keys of the recipients from known identities, and contains a trusted Private Key Generator(PKG). Encryption : inputting the message (data), public key string, and cryptosystem parameters Decryption : inputting the ciphertext and private key to the decryption algorithm
Architecture - in transit sender(content source) : S receiver(phone) : R identity for participant s : I s public/private key of a : K a + /K a - content : m police for m : p m Delivery of SMS/MMS:
Architecture - in transit Delivery of one-time 128-bit AES symmetric key : k e
Architecture - on platform Policy Enforcement on Initial Recipients
Architecture - on platform traffic is opaque to Android Use the Apache Mime4j library to parse the message streams in plain RFC-882 and MIME formatsApache Mime4j
Architecture - on platform Policy Enforcement on Documents at Rest add an extra policy field to the structure of each Content Provider record The Porscha mediator inserts the policy into this field
Architecture - on platform Enforcement on Indirect Receivers
EVALUATION
Discussion Recipients Without Porscha store all modifications such as decrypted s and those with information removed, locally on the phone, and only reflect back to the IMAP server the original Application and Platform Trust Alternative Application Enforcement Infrastructures Digital Rights Management Porscha is lightweight and designed with mobile solutions in mind; by contrast, many advanced DRM protocols are heavyweight and not transparent to applications.
Conclusion Porscha can protect SMS, MMS, document. Porscha secures content delivery using identity- based encryption and mediates on-platform content handling to ensure conformance with content policy
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