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DTSTART:20260308T070000
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DTSTART;TZID=America/Toronto:20260313T103000
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URL:https://uwaterloo.ca/combinatorics-and-optimization/events/crypto-readi
 ng-group-huanhuan-chen-updatable-encryption
SUMMARY:Crypto Reading Group - Huanhuan Chen-Updatable Encryption
CLASS:PUBLIC
DESCRIPTION:SPEAKER:\n\n Huanhuan Chen\n\nAFFILIATION:\n University of Wate
 rloo\n\nLOCATION:\n MC 6029\n\nABSTRACT:Updatable encryption (UE) enables 
 a cloud server to update\nciphertexts using client-generated tokens. There
  are two types of UE:\nciphertext-independent (c-i) and ciphertext-depende
 nt (c-d). In terms\nof construction and efficiency\, c-i UE utilizes a sin
 gle token to\nupdate all ciphertexts. The update mechanism relies mainly o
 n the\nhomomorphic properties of exponentiation\, which limits the efficie
 ncy\nof encryption and updating. Although c-d UE may seem inconvenient as\
 nit requires downloading parts of the ciphertexts during token\ngeneration
 \, it allows for easy implementation of the Dec-then-Enc\nstructure. This 
 methodology significantly simplifies the construction\nof the update mecha
 nism. Notably\, the c-d UE scheme proposed by Boneh\net al. (ASIACRYPT’2
 0) has been reported to be 200 times faster than\nprior UE schemes based o
 n DDH hardness\, which is the case for most\nexisting c-i UE schemes. Furt
 hermore\, c-d UE ensures a high level of\nsecurity as the token does not r
 eveal any information about the key\,\nwhich is difficult for c-i UE to ac
 hieve. However\, previous security\nstudies on c-d UE only addressed selec
 tive security\; the studies for\nadaptive security remain an open problem.
 \n\nIn this study\, we make three significant contributions to\nciphertext
 -dependent updatable encryption (c-d UE). Firstly\, we\nprovide stronger s
 ecurity notions compared to previous work\, which\ncapture adaptive securi
 ty and also consider the adversary’s\ndecryption capabilities under the 
 adaptive corruption setting.\nSecondly\, we propose a new c-d UE scheme th
 at achieves the proposed\nsecurity notions. The token generation technique
  significantly differs\nfrom the previous Dec-then-Enc structure\, while s
 till preventing key\nleakages. At last\, we introduce a packing technique 
 that enables the\nsimultaneous encryption and updating of multiple message
 s within a\nsingle ciphertext. This technique helps alleviate the cost of 
 c-d UE\nby reducing the need to download partial ciphertexts during token\
 ngeneration.
DTSTAMP:20260413T010113Z
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