3 ms·

> You can split it so that each subgroup of the five can reconstruct the entire phrase. How? Example: Split a secret phrase ("correct horse battery staple") be

> You can split it so that each subgroup of the five can reconstruct the entire phrase. How? Example: Split a secret phrase ("correct horse battery staple") between 4 friends with a quorum of 2. - Alice: correct - Bob: horse - Carol: battery - Dave: staple Great! But that's a quorum of 4. How do we reduce it to 2? Each person needs two words: - Alice: correct horse - Bob: battery staple - Carol: correct horse - Dave: battery staple But what if Alice and Carol want to get the secret? Or Bob and Dave? Well, each person needs the entire secret. - Alice: correct horse battery staple - Bob: correct horse battery staple - Carol: correct horse battery staple - Dave: correct horse battery staple ...but now the quorum is 1, and all of them just have a copy of your secret. If you want to be able to have arbitrary quorums, you need cryptography.

Udik 6y ago
Secret phrases are (typically) made of between 12 and 24 words.
- jhardy54 6y ago
  Please try the above examples with 12 or 24 words if you think that will make it easier. Example: Secret: either "a b c d e f g h i j k l" or "a b c d e f g h i j k l m n o p q r s t u v w x" Participants: Alice, Bob, Carol, Dave Quorum: 2 Which parts of the secret does each participant receive? Every combination of participant pairs must be able to recreate the full secret No single participant may have the full secret. --- HN won't let me reply to the below comment so I'll copy and paste here: > It's actually trivially possible [...] for [...] very long (60 words+) passphrases. It is not. It doesn't matter if your passphrases is 6000 words, you can't have 4 participants with a quorum of 2. > https://iancoleman.io/slip39/ https://iancoleman.io/slip39/ This uses the exact cryptography that I said you'd need. This isn't just "mnemonic phrase split between three person's", it's literally Shamir's Secret Sharing.
  - Udik 6y ago
    It's actually trivially possible but the entropy for each shard will be abysmally low, requiring very long (60 words+) passphrases. So you're right, there's no trivial way (by hand) to split a 24 passphrase in 5 shards. However, it feels like a detail: such sharding is possible even if it's not trivial: https://iancoleman.io/slip39/ https://iancoleman.io/slip39/
  - Udik 6y ago
    Sorry, but what's wrong (apart the low entropy of each shard) with: Al Bob Car Dav a: - x x x b: x - x x c: x x - x d: x x x - e: - x x x f: x - x x ....etc?
    - jhardy54 6y ago
      Clever! I hadn't considered that.

Udik 6y ago

Secret phrases are (typically) made of between 12 and 24 words.

jhardy54 6y ago
Please try the above examples with 12 or 24 words if you think that will make it easier. Example: Secret: either "a b c d e f g h i j k l" or "a b c d e f g h i j k l m n o p q r s t u v w x" Participants: Alice, Bob, Carol, Dave Quorum: 2 Which parts of the secret does each participant receive? Every combination of participant pairs must be able to recreate the full secret No single participant may have the full secret. --- HN won't let me reply to the below comment so I'll copy and paste here: > It's actually trivially possible [...] for [...] very long (60 words+) passphrases. It is not. It doesn't matter if your passphrases is 6000 words, you can't have 4 participants with a quorum of 2. > https://iancoleman.io/slip39/ https://iancoleman.io/slip39/ This uses the exact cryptography that I said you'd need. This isn't just "mnemonic phrase split between three person's", it's literally Shamir's Secret Sharing.
- Udik 6y ago
  It's actually trivially possible but the entropy for each shard will be abysmally low, requiring very long (60 words+) passphrases. So you're right, there's no trivial way (by hand) to split a 24 passphrase in 5 shards. However, it feels like a detail: such sharding is possible even if it's not trivial: https://iancoleman.io/slip39/ https://iancoleman.io/slip39/
- Udik 6y ago
  Sorry, but what's wrong (apart the low entropy of each shard) with: Al Bob Car Dav a: - x x x b: x - x x c: x x - x d: x x x - e: - x x x f: x - x x ....etc?
  - jhardy54 6y ago
    Clever! I hadn't considered that.