[Resource Topic] 2001/009: Robust key-evolving public key encryption schemes

Welcome to the resource topic for 2001/009

Robust key-evolving public key encryption schemes

Authors: Wen-Guey Tzeng, Zhi-Jia Tzeng


We propose a key-evolving paradigm to deal with the key
exposure problem of public key encryption schemes.
The key evolving paradigm is like the one used for
forward-secure digital signature schemes.
Let time be divided into time periods such that
at time period j, the decryptor holds the secret key
SK_j, while the public key PK is fixed during its
At time period j, a sender encrypts a message m as
\langle j, c\rangle, which can be decrypted only
with the private key SK_j.
When the time makes a transit from period j to j+1, the
decryptor updates its private key from SK_j to SK_{j+1}
and deletes SK_j immediately.
The key-evolving paradigm assures that compromise of the
private key SK_j does not jeopardize the message encrypted
at the other time periods.
We propose two key-evolving public key encryption schemes
with z-resilience such that compromise of z private keys
does not affect confidentiality of messages encrypted in
other time periods.
Assuming that the DDH problem is hard,
we show one scheme semantically secure against passive
adversaries and the other scheme semantically secure against
the adaptive chosen ciphertext attack under the random

ePrint: https://eprint.iacr.org/2001/009

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