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SUMMARY:Reducing Metadata Leakage from Encrypted Files and Communication -
  Nikitin Kirill\, Decentralized/Distributed Systems Lab\, EPFL
DTSTART:20191015T130000Z
DTEND:20191015T140000Z
UID:TALK132616@talks.cam.ac.uk
CONTACT:Alexander Vetterl
DESCRIPTION:Most encrypted data formats leak metadata via their plaintext 
 headers\, such as format version\, encryption schemes used\, number of rec
 ipients who can decrypt the data\, and even the recipients' identities. Th
 is leakage can pose security and privacy risks to users\, e.g.\, by reveal
 ing the full membership of a group of collaborators from a single encrypte
 d e-mail\, or by enabling an eavesdropper to fingerprint the precise encry
 ption software version and configuration the sender used. We propose that 
 future encrypted data formats improve security and privacy hygiene by prod
 ucing Padded Uniform Random Blobs or PURBs: ciphertexts indistinguishable 
 from random bit strings to anyone without a decryption key. A PURB's conte
 nt leaks nothing at all\, even the application that created it\, and is pa
 dded such that even its length leaks as little as possible. Encoding and d
 ecoding ciphertexts with no cleartext markers presents efficiency challeng
 es\, however. We present cryptographically agile encodings enabling legiti
 mate recipients to decrypt a PURB efficiently\, even when encrypted for an
 y number of recipients' public keys and/or passwords\, and when these publ
 ic keys are from different cryptographic suites. PURBs employ Padmé\, a n
 ovel padding scheme that limits information leakage via ciphertexts of max
 imum length M to a practical optimum of O(loglog M) bits\, comparable to p
 adding to a power of two\, but with lower overhead of at most 12% and decr
 easing with larger payloads.\n\nBio:\nKirill Nikitin is a fifth-year Ph.D.
  student in the Decentralized/Distributed Systems lab at École polytechni
 que fédérale de Lausanne (EPFL) advised by Prof. Bryan Ford. His researc
 h spans the topics in Privacy\, Systems Security\, and Blockchains. His pr
 imary interest at the moment is on designing encryption schemes and securi
 ty protocols that provide improved metadata protection.\nCurrently\, Kiril
 l is doing an internship in the Confidential Computing group at Microsoft 
 Research\, Cambridge.\nFor the detailed bio\, see https://nikirill.com/.\n
LOCATION:LT2\, Computer Laboratory\, William Gates Building
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