SLIP-0039: Shamir's Secret-Sharing for Mnemonic Codes

SLIP-0039: Shamir's Secret-Sharing for Mnemonic Codes
2018-09-21 19:29 ` Christopher Allen
  2018-09-24 19:49 ` Ignacio Berrozpe
  
From: Andrew Kozlik @ 2018-09-20 16:19 UTC (permalink / raw)
  To: bitcoin-dev

Hello everyone,

We are currently writing a new specification for splitting BIP-32 master
seeds into multiple mnemonics using Shamir's secret sharing scheme. We
would be interested in getting your feedback with regard to the
high-level design of the new spec:
https://github.com/satoshilabs/slips/blob/master/slip-0039.md
Please focus your attention on the section entitled "Master secret
derivation functions", which proposes several different solutions. Note
that there is a Design Rationale section at the very end of the
document, which should answer some of the questions you may have. The
document is a work in progress and we are aware that some technical
details have not been fully specified. These will be completed once the
high level design has been settled.

Thanks,

Andrew Kozlik
TREZOR Team




 permalink raw reply	[|nested]
2018-09-20 16:19 [bitcoin-dev] SLIP-0039: Shamir's Secret-Sharing for Mnemonic Codes Andrew Kozlik

  2018-09-22  4:54   ` vizeet srivastava
  2018-09-26 12:12   ` Andrew Kozlik
  2018-09-24 19:49 ` Ignacio Berrozpe
  
From: Christopher Allen @ 2018-09-21 19:29 UTC (permalink / raw)
  To: andrew.kozlik, Bitcoin Protocol Discussion

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On Fri, Sep 21, 2018 at 11:18 AM Andrew Kozlik via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> We are currently writing a new specification for splitting BIP-32 master
> seeds into multiple mnemonics using Shamir's secret sharing scheme. We
> would be interested in getting your feedback with regard to the
> high-level design of the new spec:
> https://github.com/satoshilabs/slips/blob/master/slip-0039.md
> Please focus your attention on the section entitled "Master secret
> derivation functions", which proposes several different solutions. Note
> that there is a Design Rationale section at the very end of the
> document, which should answer some of the questions you may have. The
> document is a work in progress and we are aware that some technical
> details have not been fully specified. These will be completed once the
> high level design has been settled.
>

I and a number of companies & communities I am involved with are very
interested in this.

A challenge is that Shamir Secret Sharing has subtleties. To quote Greg
Maxwell:

> I think Shamir Secret Sharing (and a number of other things, RNGs for
example), suffer from a property where they are just complex enough that
people are excited to implement them often for little good reason, and then
they are complex enough (or have few enough reasons to invest significant
time) they implement them poorly”.

Some questions for you:

* What other teams or communities besides Trezor are committed to
standardizing a Shamir Secret Sharing Scheme? I can say that the
#RebootingWebOfTrust community (meeting again for the 7th time next week in
Toronto https://rwot7.eventbrite.com) are very interested.

* Where do you want to hold discussions on this? Do people object to having
this discussion on this mailing list? Or should it be issues in SLIPS repo
or on some other mailing list?

* Presuming a successful split of secrets, I don’t know all the adversarial
problems that are associated with recovery of a SSS. As this would be an
interactive event, I presume an attacker can DOS a request to reassemble
keys (so maybe some the of integrity of each share vs all is required). And
of course there are the biggest problems:  impersonation of a reassembly
request and a MitM of a reassembly request. Are there other attacks? Are
you trying to mitigate any of these?

Two comments:

* The Lightning Network community has added to their BIP32 mnemonics the
ability to have a birthday in the seed, to make it easier  to scan the
blockchain for keys, as well as a byte with some way to know how to derive
keys paths for it. I don’t seee a BOLT for this (it was mentioned in
https://bitcoin.stackexchange.com/questions/74805/what-is-birthday-in-the-context-of-bip39-lightning-seed-generation)
 I would suggest that you also get some of their latest thoughts and
incorporate them.

* I worked with Chris Vickery while at Blockstrham on various possible ways
to improve mnemonic word lists. I’m not suggesting that you necessarily go
as far as we did to try to create a mnemonic that is iambic pentameter
poetry (inspired by
https://www.isi.edu/natural-language/mt/memorize-random-60.pdf), however,
we did find sources for words that are concrete (for example table is more
concrete than truth
http://crr.ugent.be/papers/Brysbaert_Warriner_Kuperman_BRM_Concreteness_ratings.pdf
) or have strong emotional valence attachment (truth is more emotional than
table), both of which make can words more memorable. I also found lists of
words that are hard to pronounce unless you are English native, and
eliminated them from my own list.

Among the results of this was a new BIP-39 2048 word compatible word list
filtered for memorability (concreteness & emotional valence) and
suitability for iambic pentameter, which is located:


https://github.com/ChristopherA/iambic-mnemonic/blob/master/word-lists/iambic-wordlist.json


…which was created from the repo at

    https://github.com/ChristopherA/password_poem

You can a number of other word lists that I’ve collected here
https://github.com/ChristopherA/iambic-mnemonic/blob/master/word-lists/

If you want to replicate what we did with your own criteria, you may want
to incorporate information from the CMU dictitionary
http://www.speech.cs.cmu.edu/cgi-bin/cmudict, the top 5000 words
https://github.com/ChristopherA/password_poem/blob/master/top5000.json,
 concrete word lists
http://crr.ugent.be/papers/Concreteness_ratings_Brysbaert_et_al_BRM.txt and
emotional words  (valence) http://crr.ugent.be/archives/1003

— Christopher Allen

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2018-09-21 19:29 ` Christopher Allen

  2018-09-26 12:12   ` Andrew Kozlik
  
From: vizeet srivastava @ 2018-09-22  4:54 UTC (permalink / raw)
  To: Christopher Allen, Bitcoin Protocol Discussion

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I see one benefit which i am looking for. I may not need to use all public
keys in p2sh script instead i can use p2pkh and retrieve funds by using
threshold number of keys..so in case i loose a public key along with
private key i still may have other public key private key pairs to
retrieve. For me it sounds interesting. I need to understand how it is
going to get implemented in more detail.

On Sat 22 Sep, 2018, 9:53 AM Christopher Allen via bitcoin-dev, <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> On Fri, Sep 21, 2018 at 11:18 AM Andrew Kozlik via bitcoin-dev <
> bitcoin-dev@lists•linuxfoundation.org> wrote:
>
>> We are currently writing a new specification for splitting BIP-32 master
>> seeds into multiple mnemonics using Shamir's secret sharing scheme. We
>> would be interested in getting your feedback with regard to the
>> high-level design of the new spec:
>> https://github.com/satoshilabs/slips/blob/master/slip-0039.md
>> Please focus your attention on the section entitled "Master secret
>> derivation functions", which proposes several different solutions. Note
>> that there is a Design Rationale section at the very end of the
>> document, which should answer some of the questions you may have. The
>> document is a work in progress and we are aware that some technical
>> details have not been fully specified. These will be completed once the
>> high level design has been settled.
>>
>
> I and a number of companies & communities I am involved with are very
> interested in this.
>
> A challenge is that Shamir Secret Sharing has subtleties. To quote Greg
> Maxwell:
>
> > I think Shamir Secret Sharing (and a number of other things, RNGs for
> example), suffer from a property where they are just complex enough that
> people are excited to implement them often for little good reason, and then
> they are complex enough (or have few enough reasons to invest significant
> time) they implement them poorly”.
>
> Some questions for you:
>
> * What other teams or communities besides Trezor are committed to
> standardizing a Shamir Secret Sharing Scheme? I can say that the
> #RebootingWebOfTrust community (meeting again for the 7th time next week in
> Toronto https://rwot7.eventbrite.com) are very interested.
>
> * Where do you want to hold discussions on this? Do people object to
> having this discussion on this mailing list? Or should it be issues in
> SLIPS repo or on some other mailing list?
>
> * Presuming a successful split of secrets, I don’t know all the
> adversarial problems that are associated with recovery of a SSS. As this
> would be an interactive event, I presume an attacker can DOS a request to
> reassemble keys (so maybe some the of integrity of each share vs all is
> required). And of course there are the biggest problems:  impersonation of
> a reassembly request and a MitM of a reassembly request. Are there other
> attacks? Are you trying to mitigate any of these?
>
> Two comments:
>
> * The Lightning Network community has added to their BIP32 mnemonics the
> ability to have a birthday in the seed, to make it easier  to scan the
> blockchain for keys, as well as a byte with some way to know how to derive
> keys paths for it. I don’t seee a BOLT for this (it was mentioned in
> https://bitcoin.stackexchange.com/questions/74805/what-is-birthday-in-the-context-of-bip39-lightning-seed-generation)
>  I would suggest that you also get some of their latest thoughts and
> incorporate them.
>
> * I worked with Chris Vickery while at Blockstrham on various possible
> ways to improve mnemonic word lists. I’m not suggesting that you
> necessarily go as far as we did to try to create a mnemonic that is iambic
> pentameter poetry (inspired by
> https://www.isi.edu/natural-language/mt/memorize-random-60.pdf), however,
> we did find sources for words that are concrete (for example table is more
> concrete than truth
> http://crr.ugent.be/papers/Brysbaert_Warriner_Kuperman_BRM_Concreteness_ratings.pdf
> ) or have strong emotional valence attachment (truth is more emotional than
> table), both of which make can words more memorable. I also found lists of
> words that are hard to pronounce unless you are English native, and
> eliminated them from my own list.
>
> Among the results of this was a new BIP-39 2048 word compatible word list
> filtered for memorability (concreteness & emotional valence) and
> suitability for iambic pentameter, which is located:
>
>
> https://github.com/ChristopherA/iambic-mnemonic/blob/master/word-lists/iambic-wordlist.json
>
>
> …which was created from the repo at
>
>     https://github.com/ChristopherA/password_poem
>
> You can a number of other word lists that I’ve collected here
> https://github.com/ChristopherA/iambic-mnemonic/blob/master/word-lists/
>
> If you want to replicate what we did with your own criteria, you may want
> to incorporate information from the CMU dictitionary
> http://www.speech.cs.cmu.edu/cgi-bin/cmudict, the top 5000 words
> https://github.com/ChristopherA/password_poem/blob/master/top5000.json,
>  concrete word lists
> http://crr.ugent.be/papers/Concreteness_ratings_Brysbaert_et_al_BRM.txt
> and emotional words  (valence) http://crr.ugent.be/archives/1003
>
> — Christopher Allen
>
>
>
>
>
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists•linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>

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2018-09-20 16:19 [bitcoin-dev] SLIP-0039: Shamir's Secret-Sharing for Mnemonic Codes Andrew Kozlik
  2018-09-21 19:29 ` Christopher Allen

  2018-09-26 13:44   ` Andrew Kozlik
  
From: Ignacio Berrozpe @ 2018-09-24 19:49 UTC (permalink / raw)
  To: andrew.kozlik, bitcoin-dev


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Hi Andrew

Please allow me to comment on your work, as I happened to publish an
article 5 months ago proposing SSS to split bitcoins private keys into
shares that could be encoded directly using BIP-0039 mnemonic words. While
cryptographically much simpler than your proposal, the proposal had the
characteristic that it could be applied directly to existing private keys
backups, by splitting the keys into SSS shares that could benefit from the
existing BIP-0039 mnemonic to encode directly the shares. I thought it
would be a simple path for hardware wallets providers such as Trezor into
providing a better/more secure alternative the existing BIP-0039 privatekey
backups of 24 words.

The article can be found here, and I've enclosed a simplified version

https://privatekeys.org/2018/04/24/k-of-m-private-key-generation-and-backup-in-bitcoin-wallets/

Mind two questions? Your proposed work provides a way to split the
pre-secret into SSS shares, a format of encoding the shares, and finally
several methods to derive the master secret from the pre-secret. Would you
envision standarizing these different topics under the same proposal? Also,
have you thought of a way to deal with the existing legacy privatekeys
already encoded into BIP-0039, or stored in other formats, and how to
migrate them securely into a schema of encoded SSS shares?

Best regards
Ignacio Berrozpe







On Fri, Sep 21, 2018 at 8:18 PM Andrew Kozlik via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> Hello everyone,
>
> We are currently writing a new specification for splitting BIP-32 master
> seeds into multiple mnemonics using Shamir's secret sharing scheme. We
> would be interested in getting your feedback with regard to the
> high-level design of the new spec:
> https://github.com/satoshilabs/slips/blob/master/slip-0039.md
> Please focus your attention on the section entitled "Master secret
> derivation functions", which proposes several different solutions. Note
> that there is a Design Rationale section at the very end of the
> document, which should answer some of the questions you may have. The
> document is a work in progress and we are aware that some technical
> details have not been fully specified. These will be completed once the
> high level design has been settled.
>
> Thanks,
>
> Andrew Kozlik
> TREZOR Team
>
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists•linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>

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 permalink raw reply	[|nested]
2018-09-21 19:29 ` Christopher Allen
  2018-09-22  4:54   ` vizeet srivastava

  
From: Andrew Kozlik @ 2018-09-26 12:12 UTC (permalink / raw)
  To: Christopher Allen, Bitcoin Protocol Discussion

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Thanks for your input Christopher. Since we already have the discussion
about your comments running under the issues in the SLIPs repo on Github
(https://github.com/satoshilabs/slips/issues), let's continue it there.

Andrew Kozlik


On 21.9.2018 21:29, Christopher Allen wrote:
> On Fri, Sep 21, 2018 at 11:18 AM Andrew Kozlik via bitcoin-dev
> <bitcoin-dev@lists•linuxfoundation.org
> <mailto:bitcoin-dev@lists•linuxfoundation.org>> wrote:
>
>     We are currently writing a new specification for splitting BIP-32
>     master
>     seeds into multiple mnemonics using Shamir's secret sharing scheme. We
>     would be interested in getting your feedback with regard to the
>     high-level design of the new spec:
>     https://github.com/satoshilabs/slips/blob/master/slip-0039.md
>     Please focus your attention on the section entitled "Master secret
>     derivation functions", which proposes several different solutions.
>     Note
>     that there is a Design Rationale section at the very end of the
>     document, which should answer some of the questions you may have. The
>     document is a work in progress and we are aware that some technical
>     details have not been fully specified. These will be completed
>     once the
>     high level design has been settled.
>
>
> I and a number of companies & communities I am involved with are very
> interested in this. 
>
> A challenge is that Shamir Secret Sharing has subtleties. To quote
> Greg Maxwell:
>
> > I think Shamir Secret Sharing (and a number of other things, RNGs
> for example), suffer from a property where they are just complex
> enough that people are excited to implement them often for little good
> reason, and then they are complex enough (or have few enough reasons
> to invest significant time) they implement them poorly”.
>
> Some questions for you:
>
> * What other teams or communities besides Trezor are committed to
> standardizing a Shamir Secret Sharing Scheme? I can say that the
> #RebootingWebOfTrust community (meeting again for the 7th time next
> week in Toronto https://rwot7.eventbrite.com) are very interested.
>
> * Where do you want to hold discussions on this? Do people object to
> having this discussion on this mailing list? Or should it be issues in
> SLIPS repo or on some other mailing list? 
>
> * Presuming a successful split of secrets, I don’t know all the
> adversarial problems that are associated with recovery of a SSS. As
> this would be an interactive event, I presume an attacker can DOS a
> request to reassemble keys (so maybe some the of integrity of each
> share vs all is required). And of course there are the biggest
> problems:  impersonation of a reassembly request and a MitM of a
> reassembly request. Are there other attacks? Are you trying to
> mitigate any of these?
>
> Two comments:
>
> * The Lightning Network community has added to their BIP32 mnemonics
> the ability to have a birthday in the seed, to make it easier  to scan
> the blockchain for keys, as well as a byte with some way to know how
> to derive keys paths for it. I don’t seee a BOLT for this (it was
> mentioned
> in https://bitcoin.stackexchange.com/questions/74805/what-is-birthday-in-the-context-of-bip39-lightning-seed-generation)
>  I would suggest that you also get some of their latest thoughts and
> incorporate them.
>
> * I worked with Chris Vickery while at Blockstrham on various possible
> ways to improve mnemonic word lists. I’m not suggesting that you
> necessarily go as far as we did to try to create a mnemonic that is
> iambic pentameter poetry (inspired by
> https://www.isi.edu/natural-language/mt/memorize-random-60.pdf),
> however, we did find sources for words that are concrete (for example
> table is more concrete than truth
> http://crr.ugent.be/papers/Brysbaert_Warriner_Kuperman_BRM_Concreteness_ratings.pdf
> ) or have strong emotional valence attachment (truth is more emotional
> than table), both of which make can words more memorable. I also found
> lists of words that are hard to pronounce unless you are English
> native, and eliminated them from my own list. 
>
> Among the results of this was a new BIP-39 2048 word compatible word
> list filtered for memorability (concreteness & emotional valence) and
> suitability for iambic pentameter, which is located:
>
>    
> https://github.com/ChristopherA/iambic-mnemonic/blob/master/word-lists/iambic-wordlist.json 
>
> …which was created from the repo at
>
>     https://github.com/ChristopherA/password_poem
>
> You can a number of other word lists that I’ve collected here
> https://github.com/ChristopherA/iambic-mnemonic/blob/master/word-lists/
>
> If you want to replicate what we did with your own criteria, you may
> want to incorporate information from the CMU
> dictitionary http://www.speech.cs.cmu.edu/cgi-bin/cmudict, the top
> 5000
> words https://github.com/ChristopherA/password_poem/blob/master/top5000.json,
>  concrete word lists
> http://crr.ugent.be/papers/Concreteness_ratings_Brysbaert_et_al_BRM.txt
> and emotional words  (valence) http://crr.ugent.be/archives/1003
>
> — Christopher Allen
>
>
>
>
>
>
>


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2018-09-24 19:49 ` Ignacio Berrozpe

  
From: Andrew Kozlik @ 2018-09-26 13:44 UTC (permalink / raw)
  To: Ignacio Berrozpe, bitcoin-dev

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Thank you for your input Ignacio. Looking at your proposal, I see that
its main feature is that it makes one of the shares privileged in the
sense that it must always take part in the reconstruction of the master
secret, while the remaining shares follow the K-of-M scheme. This is an
interesting idea.

To answer your questions:

> Your proposed work provides a way to split the pre-secret into SSS
> shares, a format of encoding the shares, and finally several methods
> to derive the master secret from the pre-secret. Would you envision
> standarizing these different topics under the same proposal?
We intend standardize the encoding format, splitting of the pre-master
secret into shares and the derivation of the master secret from the
pre-master secret in a single document. However, note that only one of
the four proposed master secret derivation functions will be selected
for the final version.

> Also, have you thought of a way to deal with the existing legacy
> privatekeys already encoded into BIP-0039, or stored in other formats,
> and how to migrate them securely into a schema of encoded SSS shares?
Three of the four proposed master secret derivation functions are
symmetric, which means that they allow users to migrate any existing
master secret (including a BIP-0039 mnemonic) to the new scheme.

Thanks,
Andrew Kozlik


On 24.9.2018 21:49, Ignacio Berrozpe wrote:
> Hi Andrew
>
> Please allow me to comment on your work, as I happened to publish an
> article 5 months ago proposing SSS to split bitcoins private keys into
> shares that could be encoded directly using BIP-0039 mnemonic words.
> While cryptographically much simpler than your proposal, the proposal
> had the characteristic that it could be applied directly to existing
> private keys backups, by splitting the keys into SSS shares that could
> benefit from the existing BIP-0039 mnemonic to encode directly the
> shares. I thought it would be a simple path for hardware wallets
> providers such as Trezor into providing a better/more secure
> alternative the existing BIP-0039 privatekey backups of 24 words.
>
> The article can be found here, and I've enclosed a simplified version
>
> https://privatekeys.org/2018/04/24/k-of-m-private-key-generation-and-backup-in-bitcoin-wallets/
>
> Mind two questions? Your proposed work provides a way to split the
> pre-secret into SSS shares, a format of encoding the shares, and
> finally several methods to derive the master secret from the
> pre-secret. Would you envision standarizing these different topics
> under the same proposal? Also, have you thought of a way to deal with
> the existing legacy privatekeys already encoded into BIP-0039, or
> stored in other formats, and how to migrate them securely into a
> schema of encoded SSS shares?
>
> Best regards
> Ignacio Berrozpe
>
>
>
>
>
>
>
> On Fri, Sep 21, 2018 at 8:18 PM Andrew Kozlik via bitcoin-dev
> <bitcoin-dev@lists•linuxfoundation.org
> <mailto:bitcoin-dev@lists•linuxfoundation.org>> wrote:
>
>     Hello everyone,
>
>     We are currently writing a new specification for splitting BIP-32
>     master
>     seeds into multiple mnemonics using Shamir's secret sharing scheme. We
>     would be interested in getting your feedback with regard to the
>     high-level design of the new spec:
>     https://github.com/satoshilabs/slips/blob/master/slip-0039.md
>     Please focus your attention on the section entitled "Master secret
>     derivation functions", which proposes several different solutions.
>     Note
>     that there is a Design Rationale section at the very end of the
>     document, which should answer some of the questions you may have. The
>     document is a work in progress and we are aware that some technical
>     details have not been fully specified. These will be completed
>     once the
>     high level design has been settled.
>
>     Thanks,
>
>     Andrew Kozlik
>     TREZOR Team
>
>
>     _______________________________________________
>     bitcoin-dev mailing list
>     bitcoin-dev@lists•linuxfoundation.org
>     <mailto:bitcoin-dev@lists•linuxfoundation.org>
>     https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>


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