Disclaimer

This is an alpha build and is currently under active development. Please be advised of the following:

• This code currently is not audited by an external security auditor, use it at your own risk
• The code has not been subjected to thorough review by engineers at the Electric Coin Company
• We are actively changing the codebase and adding features where/when needed

🔒 Security Warnings

The Lightwalletd Server is experimental and a work in progress. Use it at your own risk.

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Overview

lightwalletd is a backend service that provides a bandwidth-efficient interface to the Zcash blockchain. Currently, lightwalletd supports the Sapling protocol version as its primary concern. The intended purpose of lightwalletd is to support the development of mobile-friendly shielded light wallets.

lightwalletd is a backend service that provides a bandwidth-efficient interface to the Zcash blockchain for mobile and other wallets, such as Zecwallet.

Lightwalletd has not yet undergone audits or been subject to rigorous testing. It lacks some affordances necessary for production-level reliability. We do not recommend using it to handle customer funds at this time (October 2019).

To view status of CI pipeline

To view detailed Codecov report

Documentation for lightwalletd clients (the gRPC interface) is in docs/rtd/index.html. The current version of this file corresponds to the two .proto files; if you change these files, please regenerate the documentation by running make doc, which requires docker to be installed.

Local/Developer docker-compose Usage

docs/docker-compose-setup.md

Local/Developer Usage

Zcashd

You must start a local instance of zcashd, and its .zcash/zcash.conf file must include the following entries:

txindex=1
insightexplorer=1
experimentalfeatures=1

It's necessary to run zcashd --reindex one time for these options to take effect. This typically takes several hours, and requires more space in the .zcash data directory.

Lightwalletd uses the following zcashd RPCs:

• getblockchaininfo
• getblock
• getrawtransaction
• getaddresstxids
• sendrawtransaction

Lightwalletd

First, install Go version 1.11 or later. You can see your current version by running go version.

To build the server, run make.

This will build the server binary, where you can use the below commands to configure how it runs.

To run SERVER

Assuming you used make to build SERVER:

./server --no-tls-very-insecure=true --conf-file /home/zcash/.zcash/zcash.conf --log-file /logs/server.log --bind-addr 127.0.0.1:18232

Production Usage

Run a local instance of zcashd (see above). Ensure Go version 1.11 or later is installed.

x509 Certificates You will need to supply an x509 certificate that connecting clients will have good reason to trust (hint: do not use a self-signed one, our SDK will reject those unless you distribute them to the client out-of-band). We suggest that you be sure to buy a reputable one from a supplier that uses a modern hashing algorithm (NOT md5 or sha1) and that uses Certificate Transparency (OID 1.3.6.1.4.1.11129.2.4.2 will be present in the certificate).

To check a given certificate's (cert.pem) hashing algorithm:

openssl x509 -text -in certificate.crt | grep "Signature Algorithm"

To check if a given certificate (cert.pem) contains a Certificate Transparency OID:

echo "1.3.6.1.4.1.11129.2.4.2 certTransparency Certificate Transparency" > oid.txt
openssl asn1parse -in cert.pem -oid ./oid.txt | grep 'Certificate Transparency'

To use Let's Encrypt to generate a free certificate for your frontend, one method is to:

1. Install certbot
2. Open port 80 to your host
3. Point some forward dns to that host (some.forward.dns.com)
4. Run

certbot certonly --standalone --preferred-challenges http -d some.forward.dns.com

5. Pass the resulting certificate and key to frontend using the -tls-cert and -tls-key options.

To run production SERVER

Example using server binary built from Makefile:

./server --tls-cert cert.pem --tls-key key.pem --conf-file /home/zcash/.zcash/zcash.conf --log-file /logs/server.log --bind-addr 127.0.0.1:18232

Block cache

Lightwalletd caches all blocks from Sapling activation up to the most recent block, which takes about an hour the first time you run lightwalletd. During this syncing, lightwalletd is fully available; the only effect of being in download mode is that block fetches are slower.

After syncing, lightwalletd will start almost immediately, because the blocks are cached in local files (by default, within /var/lib/lightwalletd/db; you can specify a different location using the --data-dir command-line option).

Lightwalletd checks the consistency of these files at startup and during operation, as might be caused by an unclean shutdown, and if it detects corruption, it will recreate the cache by re-downloading all blocks from zcashd requiring an hour again, but this should occur extremely rarely.

If lightwalletd detects corruption in these cache files, it will log a message containing the string CORRUPTION and also indicate the nature of the corruption.

Pull Requests

We welcome pull requests! We like to keep our Go code neatly formatted in a standard way, which the standard tool gofmt can do. Please consider adding the following to the file .git/hooks/pre-commit in your clone:

#!/bin/sh

modified_go_files=$(git diff --cached --name-only -- '*.go')
if test "$modified_go_files"
then
    need_formatting=$(gofmt -l $modified_go_files)
    if test "$need_formatting"
    then
        echo files need formatting:
        echo gofmt -w $need_formatting
        exit 1
    fi
fi

You'll also need to make this file executable:

$ chmod +x .git/hooks/pre-commit

Doing this will prevent commits that break the standard formatting. Simply run the gofmt command as indicated and rerun the git add and git commit commands.