Distributed custody

Single-key custody has a structural problem: whoever holds the key holds the funds (or the secrets, or the credentials). Threshold custody splits the ability to act across N parties such that any T can act jointly.

This is the foundation of MPC wallets, threshold key escrow, and multi-device authentication systems.

What you get

A single key never exists on any one machine — even at generation time, the secret is split at birth.
T-of-N quorum to authorize any transaction.
Configurable policies (daily limits, multi-jurisdiction requirements, time-bounded authorizations) via the attribute DSL.
Thunderbird-style key escrow: lose your device and T-of-N trusted recoverers can restore access.

Wallet architecture

A threshold BTC or ETH wallet looks like:

[ User device ]         [ Co-signer 1 ]       [ Co-signer 2 ]
       |                       |                     |
       +-----------+-----------+---------+-----------+
                   |
                   v
           [ Coordinator ]
                   |
                   v
           [ Threshold signature ]
                   |
                   v
           [ Blockchain transaction ]

The user authorizes a transaction on their device; co-signers approve (or auto-approve under policy); the coordinator combines the partial signatures into a valid blockchain signature.

Threshold key escrow

The same architecture backs Thunderbird-style key escrow. An organization can designate N trusted recoverers (e.g. 5 IT staff); any 3 of them can restore access to a lost key. Individual recoverers cannot act alone; collective action is required.

Confium’s confium-escrow crate generalizes this pattern. The threshold T and pool N are configurable; recovery events are anchored in the transparency log for auditability.

Attribute-based policies

The threshold DSL lets you express:

2-of-3 user devices for transactions under $1000
3-of-5 security staff for transactions over $1000
5-of-7 board members for transactions over $100000

The coordinator enforces the policy at signing time.

When to choose this use case

You’re building a cryptocurrency wallet or institutional custody service.
You provide backup / recovery for end-user keys (email, identity, content encryption).
You need a multi-party approval mechanism for high-value operations.