Paper 2023/189

tlock: Practical Timelock Encryption from Threshold BLS

Nicolas Gailly, Protocol Labs
Kelsey Melissaris, Aarhus University
Yolan Romailler, Protocol Labs

We present a practical construction and implementation of timelock encryption, in which a ciphertext is guaranteed to be decryptable only after some specified time has passed. We employ an existing threshold network, the League of Entropy, implementing threshold BLS [BLS01, B03] in the context of Boneh and Franklin's identity-based encryption (IBE) [BF01]. At present this threshold network broadcasts BLS signatures over each round number, equivalent to the current time interval, and as such can be considered a decentralised key holder periodically publishing private keys for the IBE where identities are the round numbers. A noticeable advantage of this scheme is that only the encryptors and decryptors are required to perform any additional cryptographic operations; the threshold network can remain unaware of the TLE and does not have to change to support the scheme. We also release an open-source implementation of our scheme and a live web page that can be used in production now relying on the existing League of Entropy network acting as a distributed public randomness beacon service using threshold BLS signatures.

Available format(s)
Cryptographic protocols
Publication info
timelock encryptiontimelockthreshold cryptographyleague of entropy
Contact author(s)
nikkolasg @ protocol ai
kelseymelissaris @ gmail com
yolan @ protocol ai
2023-02-15: approved
2023-02-13: received
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Creative Commons Attribution


      author = {Nicolas Gailly and Kelsey Melissaris and Yolan Romailler},
      title = {tlock: Practical Timelock Encryption from Threshold BLS},
      howpublished = {Cryptology ePrint Archive, Paper 2023/189},
      year = {2023},
      note = {\url{}},
      url = {}
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