brave-payments-tools

Based on this blog post, and similar to the BitGo cli tool, but tailored more for batch-like operations.

To emphasize:

• files are transferred between the cold machine and the networked machine via USB stick;

• after one-time configuration, the cold machine is never connected to the network; and,

• recovery files are distributed to N trusted actors via USB stick, with at least M trusted actors required to co-operate in order to recovery the passphrases for the private keys.

Originally this tool worked for Bitcoin wallets using the BitGo API; the current invocation of this tool also works for BAT wallets using the Uphold API.

BAT/Uphold

Creating a Wallet

To summarize:

1. A keypair is created on the cold machine, the private key are encrypted with a user-supplied passphrase, a keychains file is prepared for the networked machine, and (partial) recovery files are generated for distribution.

2. The keychains file is used by the networked machine to create an protected wallet on the Uphold server.

On the Cold Machine

% bin/offline-create-keychains
prompt: User Keychain passphrase: ******

wrote keychains-779826ce-a74f-4d61-907a-0d238db9808f.json
wrote recovery_0_2_3-779826ce-a74f-4d61-907a-0d238db9808f.json
wrote recovery_1_2_3-779826ce-a74f-4d61-907a-0d238db9808f.json
wrote recovery_2_2_3-779826ce-a74f-4d61-907a-0d238db9808f.json

The passphrase is used to encrypt the private key for the user keychain. A strong password must be used for each (Requiring at least 10^17 guesses according to zxcvbn.) Private keys are encrypted using

sjcl.encrypt(passPhrase, privateKey, { iter: 100000, ks: 256, salt: sjcl.random.randomWords(2, 0) })

The keychains file is kept on the cold machine and transferred to the networked machine, e.g.,

{
  "userKey": {
    "label": "user",
    "xpub": "73932b241ff10386f467fc2ba5ca8ee75e72efdad2ba505488b0be0a315d04b9",
    "encryptedXprv": "...",
    "payload": {
      "requestType": "httpSignature",
      "signedTx": {
        "headers": {
          "digest": "SHA-256=od4jPanrP3J+emLcom2IhZ481Sfc0rJ77AmH+JTYoxc=",
          "signature": "...",
        },
        "body": {
          "label": "publisher-settlement-001",
          "currency": "BAT",
          "publicKey": "73932b241ff10386f467fc2ba5ca8ee75e72efdad2ba505488b0be0a315d04b9"
        },
        "octets": "..."
      }
    }
  },
  "config": {
    "env": "prod"
  }
}

The recovery files are immediately copied to N different USB sticks and then "securely" deleted from the cold machine. These recovery files can be used to reconstruct the user key using Shamir's threshold secret sharing scheme.

On the Networked Machine

% bin/online-create-wallet \
    --keychains keychains-779826ce-a74f-4d61-907a-0d238db9808f.json
prompt: OTP: ...
prompt: Application access-token: ...

wrote wallet-779826ce-a74f-4d61-907a-0d238db9808f.json

The wallet file has no sensitive information, and is kept on the networked machine, e.g.,

{
  "config": {
    "env": "prod"
  },
  "label": "publisher-settlement-001",
  "authenticate": {},
  "wallet": {
    "id": "5f83690f-5b25-40f5-820d-d0607cd0df12",
    "label": "publisher-settlement-001",
    "currency": "BAT"
  }
}

Submitting a Transaction

To summarize:

1. A payments file is prepared on the networked machine, e.g.,

    [
      {
        "publisher": "homespun.io",
        "altcurrency": "BAT",
        "probi": "8508274545667666166",
        "fees": "447803923456192956",
        "authority": "github:mrose17",
        "transactionId": "c7f33832-6db8-4ee3-98dc-ff7b1c12f9bb",
        "address": "09633c3d-1470-4ca5-ac48-df825164f6df",
        "currency": "USD"
      },
      ...
    ]

   which contains a list of publisher settlements

2. An unsigned transaction is created, and then transferred to the cold machine.

3. On the cold machine, the transaction is signed (requiring the operator to enter the passphrase for the keypair's private key).

4. The signed transaction is then transferred to the networked machine and submitted to the BitGo server.

On the Networked Machine

% bin/online-create-transaction \
    --wallet wallet-779826ce-a74f-4d61-907a-0d238db9808f.json \
    --payments payments-batch1.json 
prompt: OTP: ...
prompt: Application access-token: ...

wrote unsigned-batch1.json

This file is then transferred to the cold machine, e.g.,

{
  "config": {
    "env": "prod"
  },
  "unsignedTxs": [
    {
      "denomination": {
        "amount": "8.508274545667666166",
        "currency": "BAT"
      },
      "destination": "09633c3d-1470-4ca5-ac48-df825164f6df",
      "message": "c7f33832-6db8-4ee3-98dc-ff7b1c12f9bb",
      "id": "5f83690f-5b25-40f5-820d-d0607cd0df12",
      "label": "publisher-settlement-001"
    },
    ...
  ],
  "authenticate": {}
}

On the Cold Machine

% bin/offline-sign-transaction \
    --unsignedTx unsigned-batch1.json
prompt: User Keychain passphrase: ******

wrote signed-batch1.json

This file is then transferred to the networked machine, e.g.,

{
  "config": {
    "env": "test"
  },
  "signedTxs": [
    {
      "id": "5f83690f-5b25-40f5-820d-d0607cd0df12",
      "requestType": "httpSignature",
      "signedTx": {
        "headers": {
          "digest": "SHA-256=Cuv9iXCLZWSJ18Zo1wJkE/b1xhUEpBpySbYKC95yfEA=",
          "signature": "..."
        },
        "body": {
          "denomination": {
            "amount": "8.508274545667666166",
            "currency": "BAT"
          },
          "destination": "09633c3d-1470-4ca5-ac48-df825164f6df",
          "message": "c7f33832-6db8-4ee3-98dc-ff7b1c12f9bb"
        },
        "octets": "..."
      }
    },
    ...
  ],
  "authenticate": {}
}

On the Networked Machine

% bin/online-submit-transaction \
    --signedTx signed-batch1.json
prompt: OTP: ...
prompt: Application access-token: ...

wrote submit-batch1.json

The resulting file may be archived, e.g.,

[
  {
    "publisher": "homespun.io",
    "altcurrency": "BAT",
    "probi": "8508274545667666166",
    "fees": "447803923456192956",
    "authority": "github:mrose17",
    "transactionId": "c7f33832-6db8-4ee3-98dc-ff7b1c12f9bb",
    "address": "09633c3d-1470-4ca5-ac48-df825164f6df",
    "currency": "USD",
    "status": "completed",
    "message": "c7f33832-6db8-4ee3-98dc-ff7b1c12f9bb",
    "hash": "58361892-b073-464d-a7df-c9741ab9c8bd",
    "walletId": "5f83690f-5b25-40f5-820d-d0607cd0df12",
    "tx": "...",
    "amount": "1.57",
    "commission": "0.04",
    "fee": "0.00"
  },
  ...
]

The payments, unsigned transaction, and signed transaction files should be archived for auditing purposes.

Bitcoin/BitGo

Creating a Wallet

To summarize:

1. Two keypairs are created on the cold machine, the private keys are encrypted with user-supplied passphrases, a keychains file is prepared for the networked machine, and (partial) recovery files are generated for distribution.

2. The keychains file is used by the networked machine to create an HD wallet on the BitGo server.

On the Cold Machine

% bin/offline-create-keychains
prompt: User Keychain passphrase: ******
prompt: Backup Keychain passphrase: ******

wrote keychains-779826ce-a74f-4d61-907a-0d238db9808f.json
wrote recovery_0_2_3-779826ce-a74f-4d61-907a-0d238db9808f.json
wrote recovery_1_2_3-779826ce-a74f-4d61-907a-0d238db9808f.json
wrote recovery_2_2_3-779826ce-a74f-4d61-907a-0d238db9808f.json

The two passphrases are used to encrypt the private key for the user and backup keychains, respectively. A strong password must be used for each (Requiring at least 10^17 guesses according to zxcvbn.) Private keys are encrypted using

sjcl.encrypt(passPhrase, privateKey, { iter: 100000, ks: 256, salt: sjcl.random.randomWords(2, 0) })

The keychains file is kept on the cold machine and transferred to the networked machine, e.g.,

{
  "userKey": {
    "xpub": "xpub..."
    "label": "user",
    "encryptedXprv": "{...}"
  },
  "backupKey": {
    "xpub": "xpub...",
    "label": "backup",
    "encryptedXprv": "{...}"
  }
}

The recovery files are immediately copied to N different USB sticks, e.g.,

{
  "userKey": {
    "xpub": "xpub..."
    "label": "user",
    "encryptedXprv": "{...}",
    "share_0": "..."
  },
  "backupKey": {
    "xpub": "xpub...",
    "label": "backup",
    "encryptedXprv": "{...}",
    "share_0": "..."
  }
}

and then "securely" deleted from the cold machine. These recovery files can be used to reconstruct the user and backup keys using Shamir's threshold secret sharing scheme.

On the Networked Machine

% bin/online-create-wallet \
    --keychains keychains-779826ce-a74f-4d61-907a-0d238db9808f.json
prompt: BitGo email-address:
prompt: BitGo password-address:
prompt: OTP:
prompt: Application access-token: ...

wrote wallet-779826ce-a74f-4d61-907a-0d238db9808f.json

The wallet file has no sensitive information, and is kept on the networked machine, e.g.,

{
  "label": "779826ce-a74f-4d61-907a-0d238db9808f",
  "authenticate": {
    "username": ""
  },
  "wallet": {
    "id": "33bKSJbCoXWuue89bYhqFvSyHZ1MzvZJt8"
  }
}

Submitting a Transaction

To summarize:

1. A payments file is prepared on the networked machine, e.g.,

    { "1JQPqfRW2xKKQkFWd62MvZq2Ed7B7x8KU" : 500000 }

   which contains a list of Bitcoin addresses to be credited.

2. An unsigned transaction is created, and then transferred to the cold machine.

3. On the cold machine, the transaction is signed (requiring the operator to enter the passphrase for the user keypair's private key).

4. The signed transaction is then transferred to the networked machine and submitted to the BitGo server.

On the Networked Machine

% bin/online-create-transaction \
    --wallet wallet-779826ce-a74f-4d61-907a-0d238db9808f.json \
    --payments payments-batch1.json 
prompt: Application access-token: ...

wrote unsigned-batch1.json

This file is then transferred to the cold machine, e.g.,

{
  "transactionHex": "...",
  "unspents": [ ... ],
  "fee": 33953,
  "changeAddresses": [
    {
      "address": "3JDpx9s3Pit6BnNBQ467dJFPNjHGRAwQu9",
      "amount": 982616
    }
  ],
  "walletId": "33bKSJbCoXWuue89bYhqFvSyHZ1MzvZJt8",
  "walletKeychains": [ ... ],
  "feeRate": 51600,
  "estimatedSize": 658,
  "travelInfos": [],
  "authenticate": {
    "username": ""
  }
}

On the Cold Machine

% bin/offline-sign-transaction \
    --unsignedTx unsigned-batch1.json
prompt: User Keychain passphrase: ******

wrote signed-batch1.json

This file is then transferred to the networked machine, e.g.,

{
  "tx": "...",
  "walletId": "33bKSJbCoXWuue89bYhqFvSyHZ1MzvZJt8",
  "authenticate": {
    "username": ""
  }
}

On the Networked Machine

% bin/online-submit-transaction \
    --signedTx signed-batch1.json
prompt: Application access-token: ...

wrote submit-batch1.json

The resulting file may be archived, e.g.,

{
  "status": "accepted",
  "tx": "...",
  "hash": "e5a18cb5718844122cc1b23d898e0a03942f34b1cb90e8d8958e77e3c7b4c61c",
  "instant": false,
  "walletId": "33bKSJbCoXWuue89bYhqFvSyHZ1MzvZJt8",
  "message": "batch1"
}

The payments, unsigned transaction, and signed transaction files should be archived for auditing purposes.

Passphrase Recovery

M of the N trusted actors place their recovery files on the cold machine and run

% bin/offline-recover-passphrases *.json

This outputs the passphrases used to encrypt the private keys for the keypair(s). The recovery files should then be "securely" deleted from the third machine.