Descriptor Checksum Inconsistency #23539

<!-- Describe the issue -->

Issue:

The Checksum generated by getdescriptorinfo is not accepted when I use it in importdescriptors. The two RPC calls calculate a different checksum for the same descriptor.

<!--- What behavior did you expect? -->

I ran the following commands on MacOS with bitcoind v0.21.1 installed. Since my descriptor lacked a checksum, I used getdescriptorinfo to generate one, as I read here: https://github.com/bitcoin/bitcoin/blob/master/doc/descriptors.md#checksums

The checksum for a descriptor without one can be computed using the getdescriptorinfo RPC.

I expected the checksum generated by getdescriptorinfo to be accepted by importdescriptors. It was not.

<!--- What was the actual behavior (provide screenshots if the issue is GUI-related)? -->

The actual behavior is below. I am redacting the actual descriptors/hashes for personal privacy.

$ bitcoin-cli --version
Bitcoin Core RPC client version v0.21.1
# getdescriptorinfo generates a checksum beginning with 3a.
$ bitcoin-cli getdescriptorinfo "<DESCRIPTOR>"
{
  "descriptor": "<DESCRIPTOR>#3a...",
  "checksum": "3a...",
  "isrange": false,
  "issolvable": true,
  "hasprivatekeys": false
}
# importdescriptors rejects the checksum generated by getdescriptorinfo and calculates its own different one
$ bitcoin-cli -rpcwallet=my_wallet importdescriptors '[{ "desc": "<DESCRIPTOR>#3a...", "timestamp": "now" }]'
[
  {
    "success": false,
    "error": {
      "code": -5,
      "message": "Provided checksum '3a...' does not match computed checksum '6z...'"
    }
  }
]
# importdescriptors properly accepts the checksum provided by itself.
$ bitcoin-cli -rpcwallet=my_wallet importdescriptors '[{ "desc": "<DESCRIPTOR>#6z...", "timestamp": "now" }]' 
[
  {
    "success": true
  }
]
# Using checksum expected by importdescriptors throws an error when used in getdescriptorinfo cmd
$ bitcoin-cli getdescriptorinfo "<DESCRIPTOR>#6z..."
error code: -5
error message:
Provided checksum '6z40f68x' does not match computed checksum '3av8evsc'

System information

<!-- What version of Bitcoin Core are you using, where did you get it (website, self-compiled, etc)? -->

Bitcoin Core info: Bitcoin Core RPC client version v0.21.1 Downloaded from Bitcoin.org binary. Not compiled from source.

<!-- What type of machine are you observing the error on (OS/CPU and disk type)? -->

Machine/OS: MacOS Catalina 10.15.6 Memory 16GB

Are you sure the checksum in the "descriptor" field and the one in the "checksum" field are the same?

They can differ, because the echoed-back descriptor in the "descriptor" field is normalized (and e.g. lacks private keys), and the checksum there is computed over the echoed-back form. The "checksum" field is supposed to be for exactly your input descriptor as you provided it.

If that's not it, I fear we'll need a more concrete example to reproduce.

Yes, I just double checked this now. I am using a descriptor of the form wpkh([fp/a'/b']xpub.../c) where a,b,c are single digit ints. The output of getdescriptorinfo is exactly the same as my input.

This shouldn't be possible since they use the exact same code.

Can you share exactly the descriptors that you used (or generate descriptors that exhibit the same issue that you are willing to share)?

I just generated a new xpub and added a random fingerpint. I ran the same commands and saw the same behavior.

~ $ bitcoin-cli getdescriptorinfo "wpkh([a2bd0d5d/1'/0']xpub68hdHBdprdRvzD54QhhWYDqVVj7uxg1gK78MkkxVCD6687dJ19rqGt5dhBV1czH8n6Jhb2PPzVFwcy3fnMCPtFBmwLcDWLcP1Nxbfad1MmN/2)"
{
  "descriptor": "wpkh([a2bd0d5d/1'/0']xpub68hdHBdprdRvzD54QhhWYDqVVj7uxg1gK78MkkxVCD6687dJ19rqGt5dhBV1czH8n6Jhb2PPzVFwcy3fnMCPtFBmwLcDWLcP1Nxbfad1MmN/2)#fhgkwdud",
  "checksum": "fhgkwdud",
  "isrange": false,
  "issolvable": true,
  "hasprivatekeys": false
}
~ $ bitcoin-cli -rpcwallet=hot_wallet_1 importdescriptors '[{ "desc": "wpkh([a2bd0d5d/1'/0']xpub68hdHBdprdRvzD54QhhWYDqVVj7uxg1gK78MkkxVCD6687dJ19rqGt5dhBV1czH8n6Jhb2PPzVFwcy3fnMCPtFBmwLcDWLcP1Nxbfad1MmN/2)#fhgkwdud", "timestamp": "now" }]'
[
  {
    "success": false,
    "error": {
      "code": -5,
      "message": "Provided checksum 'fhgkwdud' does not match computed checksum 'mg62v6fs'"
    }
  }
]
~ $ bitcoin-cli -rpcwallet=hot_wallet_1 importdescriptors '[{ "desc": "wpkh([a2bd0d5d/1'/0']xpub68hdHBdprdRvzD54QhhWYDqVVj7uxg1gK78MkkxVCD6687dJ19rqGt5dhBV1czH8n6Jhb2PPzVFwcy3fnMCPtFBmwLcDWLcP1Nxbfad1MmN/2)#mg62v6fs", "timestamp": "now" }]'
[
  {
    "success": true
  }
]

Your issue is that bash is eating the ' characters in the second command.

Yep, that's it. Sorry for the waste of time. If its helpful, the example provided in the bitcoin-cli help uses single quotes, which threw me off. perhaps these should be changed up.

no worries