Shamir's Secret Sharing

Motivation

Trust is a social concept.

• Moving away from institutions and big tech, focussing on peers as holders of trust.
• Exploring relationships-based security protocols.

Shamir's Secret Sharing (1979)

Related protocols

• secure Multiparty Computation
• multisig in crypocurrencies
• darkcrystal.pw

Use cases

💳 finance 💳
🏛️ voting 🏛️
✍️ signing ✍️
📱 account recovery 📱
🎞️ archiving 🎞️
…

key vs. data distribution

Existing UX is … well …

Goal

Explore & evaluate the UX pattern of secret sharing

Key questions

• What are metaphors or visualizations that help explain the concept?

• Where does secret sharing fall short as a security mechanism?

  • Is there awareness for verification?
  • How do people select their trusted group?

This week

• Reviewed existing implementions: Briar, Sunder, (Wallets)
• Defined scope: recovery for a messaging app
• Paper prototypes, two iterations (pilot test)
• Test design 🖨️ 🍫 📆
• 7 user tests (35 minutes)
• Synthesis and write-up
• 🏃 quick demo!

Preliminary results

Highlights

• Actual recovery flow was most difficult because it required out-of-band communication
• 3 testers asked for independent verification, 2 asked for social verification, 2 did not verify at all
• Ideal thresholds: 2/2, 2-3/4, 8/10, ?/4, 2/4, 9/10, 3/4

Findings

Ranges for thresholds usually went down after the test

Asking for recovery help was easy for most; accepting to help with recovery was scary for some.

Transparency is necessary in case secret holder is unavailable. But transparency can also lead to weaponized friendship.

An account without a username???
(Backchannel doesn't come for free!)

Further explorations

• Continued opt-in? Notification when the shard has changed?
• Temporary identity when retrieving shards?
• Should secret owner get a shard by default?

Looking for…

🏕️ Implementations in the wild 🏕️
🥡 Social protocols 🥡
🖇️ Collaborators 🖇️
💰 Funders??? 💰

🧋 Thank you 🧋

Micah, C.C. et al.

Testers
C.C., Kii Kang, Lis, Mayowa Tomori, Mike,
Pia Park, Ying Tong

Community Privacy Residency
community-privacy.github.io

💜
@eviewinter.42 (Discord/Signal)