Discussion:
BIP proposal, Pay to Contract BIP43 Application
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omar shibli via bitcoin-dev
2017-08-14 06:05:35 UTC
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Hey all,

A lot of us familiar with the pay to contract protocol, and how it uses
cleverly the homomorphic property of elliptic curve encryption system to
achieve it.
Unfortunately, there is no standard specification on how to conduct such
transactions in the cyberspace.

We have developed a basic trade finance application that relies on the
original idea described in the Homomorphic Payment Addresses and the
Pay-to-Contract Protocol paper, yet we have generalized it and made it
BIP43 complaint.

We would like to share our method, and get your feedback about it,
hopefully this effort will result into a standard for the benefit of the
community.

Abstract idea:

We define the following levels in BIP32 path.
m / purpose' / coin_type' / contract_id' / *

contract_id is is an arbitrary number within the valid range of indices.

Then we define, contract base as following prefix:
m / purpose' / coin_type' / contract_id'

contract commitment address is computed as follows:
hash document using cryptographic hash function of your choice (e.g. blake2)
map hash to partial derivation path
Convert hash to binary array.
Partition the array into parts, each part length should be 16.
Convert each part to integer in decimal format.
Convert each integer to string.
Join all strings with slash `/`.
compute child public key by chaining the derivation path from step 2 with
contract base:
m/<contract_base>/<hash_derivation_path>
compute address
Example:

master private extended key:
xprv9s21ZrQH143K2JF8RafpqtKiTbsbaxEeUaMnNHsm5o6wCW3z8ySyH4UxFVSfZ8n7ESu7fgir8imbZKLYVBxFPND1pniTZ81vKfd45EHKX73
coin type: 0
contract id: 7777777

contract base computation :

derivation path:
m/999'/0'/7777777'
contract base public extended key:
xpub6CMCS9rY5GKdkWWyoeXEbmJmxGgDcbihofyARxucufdw7k3oc1JNnniiD5H2HynKBwhaem4KnPTue6s9R2tcroqkHv7vpLFBgbKRDwM5WEE

Contract content:
foo

Contract sha256 signature:
2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae

Contract partial derivation path:
11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310

Contract commitment pub key path:
m/999'/0'/7777777'/11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310
or
<contract_base_extended_pub_key>/11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310

Contract commitment pub key:
xpub6iQVNpbZxdf9QJC8mGmz7cd3Cswt2itcQofZbKmyka5jdvQKQCqYSDFj8KCmRm4GBvcQW8gaFmDGAfDyz887msEGqxb6Pz4YUdEH8gFuaiS

Contract commitment address:
17yTyx1gXPPkEUN1Q6Tg3gPFTK4dhvmM5R


You can find the full BIP draft in the following link:
https://github.com/commerceblock/pay-to-contract-protocol-specification/blob/master/bip-draft.mediawiki


Regards,
Omar
Gregory Maxwell via bitcoin-dev
2017-08-15 05:12:11 UTC
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This construction appears to me to be completely insecure.


Say my pubkey (the result of the derivation path) is P.

We agree to contract C1. A payment is made to P + G*H(C1).

But in secret, I constructed contract C2 and pubkey Q and set P = Q + G*H(C2).

Now I can take that payment (paid to Q + G*(C1) + G*H(C2)) and assert
it was in act a payment to P' + G*H(C2). (P' is simply Q + G*H(C1))

I don't see anything in the proposal that addresses this. Am I missing it?

The applications are also not clear to me, and it doesn't appear to
address durability issues (how do you avoid losing your funds if you
lose the exact contract?).




On Mon, Aug 14, 2017 at 6:05 AM, omar shibli via bitcoin-dev
Post by omar shibli via bitcoin-dev
Hey all,
A lot of us familiar with the pay to contract protocol, and how it uses
cleverly the homomorphic property of elliptic curve encryption system to
achieve it.
Unfortunately, there is no standard specification on how to conduct such
transactions in the cyberspace.
We have developed a basic trade finance application that relies on the
original idea described in the Homomorphic Payment Addresses and the
Pay-to-Contract Protocol paper, yet we have generalized it and made it BIP43
complaint.
We would like to share our method, and get your feedback about it, hopefully
this effort will result into a standard for the benefit of the community.
We define the following levels in BIP32 path.
m / purpose' / coin_type' / contract_id' / *
contract_id is is an arbitrary number within the valid range of indices.
m / purpose' / coin_type' / contract_id'
hash document using cryptographic hash function of your choice (e.g. blake2)
map hash to partial derivation path
Convert hash to binary array.
Partition the array into parts, each part length should be 16.
Convert each part to integer in decimal format.
Convert each integer to string.
Join all strings with slash `/`.
compute child public key by chaining the derivation path from step 2 with
m/<contract_base>/<hash_derivation_path>
compute address
xprv9s21ZrQH143K2JF8RafpqtKiTbsbaxEeUaMnNHsm5o6wCW3z8ySyH4UxFVSfZ8n7ESu7fgir8imbZKLYVBxFPND1pniTZ81vKfd45EHKX73
coin type: 0
contract id: 7777777
m/999'/0'/7777777'
xpub6CMCS9rY5GKdkWWyoeXEbmJmxGgDcbihofyARxucufdw7k3oc1JNnniiD5H2HynKBwhaem4KnPTue6s9R2tcroqkHv7vpLFBgbKRDwM5WEE
foo
2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae
11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310
m/999'/0'/7777777'/11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310
or
<contract_base_extended_pub_key>/11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310
xpub6iQVNpbZxdf9QJC8mGmz7cd3Cswt2itcQofZbKmyka5jdvQKQCqYSDFj8KCmRm4GBvcQW8gaFmDGAfDyz887msEGqxb6Pz4YUdEH8gFuaiS
17yTyx1gXPPkEUN1Q6Tg3gPFTK4dhvmM5R
https://github.com/commerceblock/pay-to-contract-protocol-specification/blob/master/bip-draft.mediawiki
Regards,
Omar
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omar shibli via bitcoin-dev
2017-08-15 16:40:36 UTC
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Thank you for your time Gregory, I really appreciate that.

What we are describing here is a method to embed cryptographic signatures
into a public key based on HD Wallets - BIP32.
In a practical application, we should have two cryptographic signatures
from both sides, I don't think in that case your scenario would be an issue.

More specifically in our application, we do the following construction:

contract base: m/200'/0'/<contract_number>'
payment base (merchant commitment):
contract_base/<merchant_contract_signature>
payment address (customer commitment):
contract_base/<merchant_contract_signature>/<customer_contract_signature>

payment address funds could be reclaimed only if the
customer_contract_signature is provided by the customer.

In terms of durability, our app is pretty simple at this point, we don't
store anything, we let customer download and manage the files.

I will update the BIP to address your concerns.
Post by Gregory Maxwell via bitcoin-dev
This construction appears to me to be completely insecure.
Say my pubkey (the result of the derivation path) is P.
We agree to contract C1. A payment is made to P + G*H(C1).
But in secret, I constructed contract C2 and pubkey Q and set P = Q + G*H(C2).
Now I can take that payment (paid to Q + G*(C1) + G*H(C2)) and assert
it was in act a payment to P' + G*H(C2). (P' is simply Q + G*H(C1))
I don't see anything in the proposal that addresses this. Am I missing it?
The applications are also not clear to me, and it doesn't appear to
address durability issues (how do you avoid losing your funds if you
lose the exact contract?).
On Mon, Aug 14, 2017 at 6:05 AM, omar shibli via bitcoin-dev
Post by omar shibli via bitcoin-dev
Hey all,
A lot of us familiar with the pay to contract protocol, and how it uses
cleverly the homomorphic property of elliptic curve encryption system to
achieve it.
Unfortunately, there is no standard specification on how to conduct such
transactions in the cyberspace.
We have developed a basic trade finance application that relies on the
original idea described in the Homomorphic Payment Addresses and the
Pay-to-Contract Protocol paper, yet we have generalized it and made it
BIP43
Post by omar shibli via bitcoin-dev
complaint.
We would like to share our method, and get your feedback about it,
hopefully
Post by omar shibli via bitcoin-dev
this effort will result into a standard for the benefit of the community.
We define the following levels in BIP32 path.
m / purpose' / coin_type' / contract_id' / *
contract_id is is an arbitrary number within the valid range of indices.
m / purpose' / coin_type' / contract_id'
hash document using cryptographic hash function of your choice (e.g.
blake2)
Post by omar shibli via bitcoin-dev
map hash to partial derivation path
Convert hash to binary array.
Partition the array into parts, each part length should be 16.
Convert each part to integer in decimal format.
Convert each integer to string.
Join all strings with slash `/`.
compute child public key by chaining the derivation path from step 2 with
m/<contract_base>/<hash_derivation_path>
compute address
xprv9s21ZrQH143K2JF8RafpqtKiTbsbaxEeUaMnNHsm5o6wCW3z8ySyH4Ux
FVSfZ8n7ESu7fgir8imbZKLYVBxFPND1pniTZ81vKfd45EHKX73
Post by omar shibli via bitcoin-dev
coin type: 0
contract id: 7777777
m/999'/0'/7777777'
xpub6CMCS9rY5GKdkWWyoeXEbmJmxGgDcbihofyARxucufdw7k3oc1JNnnii
D5H2HynKBwhaem4KnPTue6s9R2tcroqkHv7vpLFBgbKRDwM5WEE
Post by omar shibli via bitcoin-dev
foo
2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae
11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/
25731/49056/63882/24200/25190/59310
Post by omar shibli via bitcoin-dev
m/999'/0'/7777777'/11302/46187/26879/50831/63899/17724/
7472/16692/4930/11632/25731/49056/63882/24200/25190/59310
Post by omar shibli via bitcoin-dev
or
<contract_base_extended_pub_key>/11302/46187/26879/50831/
63899/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310
Post by omar shibli via bitcoin-dev
xpub6iQVNpbZxdf9QJC8mGmz7cd3Cswt2itcQofZbKmyka5jdvQKQCqYSDFj
8KCmRm4GBvcQW8gaFmDGAfDyz887msEGqxb6Pz4YUdEH8gFuaiS
Post by omar shibli via bitcoin-dev
17yTyx1gXPPkEUN1Q6Tg3gPFTK4dhvmM5R
https://github.com/commerceblock/pay-to-contract-
protocol-specification/blob/master/bip-draft.mediawiki
Post by omar shibli via bitcoin-dev
Regards,
Omar
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Omar Shibli via bitcoin-dev
2017-09-01 07:16:41 UTC
Permalink
Raw Message
Hello Gregory,

Thanks for you feedback.

The BIP has been updated to explicitly specify the multiparty key
derivation scheme which hopefully addresses your concerns.

Please have a look at the updated draft of the BIP at the link below:

https://github.com/commerceblock/pay-to-contract-protocol-specification/blob/master/bip-draft.mediawiki

Any feedback is highly appreciated.

Regards,
Omar
Post by omar shibli via bitcoin-dev
Thank you for your time Gregory, I really appreciate that.
What we are describing here is a method to embed cryptographic signatures
into a public key based on HD Wallets - BIP32.
In a practical application, we should have two cryptographic signatures
from both sides, I don't think in that case your scenario would be an issue.
contract base: m/200'/0'/<contract_number>'
payment base (merchant commitment): contract_base/<merchant_
contract_signature>
payment address (customer commitment): contract_base/<merchant_
contract_signature>/<customer_contract_signature>
payment address funds could be reclaimed only if the
customer_contract_signature is provided by the customer.
In terms of durability, our app is pretty simple at this point, we don't
store anything, we let customer download and manage the files.
I will update the BIP to address your concerns.
Post by Gregory Maxwell via bitcoin-dev
This construction appears to me to be completely insecure.
Say my pubkey (the result of the derivation path) is P.
We agree to contract C1. A payment is made to P + G*H(C1).
But in secret, I constructed contract C2 and pubkey Q and set P = Q + G*H(C2).
Now I can take that payment (paid to Q + G*(C1) + G*H(C2)) and assert
it was in act a payment to P' + G*H(C2). (P' is simply Q + G*H(C1))
I don't see anything in the proposal that addresses this. Am I missing it?
The applications are also not clear to me, and it doesn't appear to
address durability issues (how do you avoid losing your funds if you
lose the exact contract?).
On Mon, Aug 14, 2017 at 6:05 AM, omar shibli via bitcoin-dev
Post by omar shibli via bitcoin-dev
Hey all,
A lot of us familiar with the pay to contract protocol, and how it uses
cleverly the homomorphic property of elliptic curve encryption system to
achieve it.
Unfortunately, there is no standard specification on how to conduct such
transactions in the cyberspace.
We have developed a basic trade finance application that relies on the
original idea described in the Homomorphic Payment Addresses and the
Pay-to-Contract Protocol paper, yet we have generalized it and made it
BIP43
Post by omar shibli via bitcoin-dev
complaint.
We would like to share our method, and get your feedback about it,
hopefully
Post by omar shibli via bitcoin-dev
this effort will result into a standard for the benefit of the
community.
Post by omar shibli via bitcoin-dev
We define the following levels in BIP32 path.
m / purpose' / coin_type' / contract_id' / *
contract_id is is an arbitrary number within the valid range of indices.
m / purpose' / coin_type' / contract_id'
hash document using cryptographic hash function of your choice (e.g.
blake2)
Post by omar shibli via bitcoin-dev
map hash to partial derivation path
Convert hash to binary array.
Partition the array into parts, each part length should be 16.
Convert each part to integer in decimal format.
Convert each integer to string.
Join all strings with slash `/`.
compute child public key by chaining the derivation path from step 2
with
Post by omar shibli via bitcoin-dev
m/<contract_base>/<hash_derivation_path>
compute address
xprv9s21ZrQH143K2JF8RafpqtKiTbsbaxEeUaMnNHsm5o6wCW3z8ySyH4Ux
FVSfZ8n7ESu7fgir8imbZKLYVBxFPND1pniTZ81vKfd45EHKX73
Post by omar shibli via bitcoin-dev
coin type: 0
contract id: 7777777
m/999'/0'/7777777'
xpub6CMCS9rY5GKdkWWyoeXEbmJmxGgDcbihofyARxucufdw7k3oc1JNnnii
D5H2HynKBwhaem4KnPTue6s9R2tcroqkHv7vpLFBgbKRDwM5WEE
Post by omar shibli via bitcoin-dev
foo
2c26b46b68ffc68ff99b453c1d30413413422d706483bfa0f98a5e886266e7ae
11302/46187/26879/50831/63899/17724/7472/16692/4930/11632/25
731/49056/63882/24200/25190/59310
Post by omar shibli via bitcoin-dev
m/999'/0'/7777777'/11302/46187/26879/50831/63899/17724/7472/
16692/4930/11632/25731/49056/63882/24200/25190/59310
Post by omar shibli via bitcoin-dev
or
<contract_base_extended_pub_key>/11302/46187/26879/50831/638
99/17724/7472/16692/4930/11632/25731/49056/63882/24200/25190/59310
Post by omar shibli via bitcoin-dev
xpub6iQVNpbZxdf9QJC8mGmz7cd3Cswt2itcQofZbKmyka5jdvQKQCqYSDFj
8KCmRm4GBvcQW8gaFmDGAfDyz887msEGqxb6Pz4YUdEH8gFuaiS
Post by omar shibli via bitcoin-dev
17yTyx1gXPPkEUN1Q6Tg3gPFTK4dhvmM5R
https://github.com/commerceblock/pay-to-contract-protocol-
specification/blob/master/bip-draft.mediawiki
Post by omar shibli via bitcoin-dev
Regards,
Omar
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bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
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