Bitcoin Core is the client software directly descended from the original Bitcoin software client first released by Satoshi Nakamoto. Bitcoin Core consists of both "full-node" software which can fully validate the blockchain, as well as a Bitcoin wallet.  The official open source project that maintains and releases the software can be found here [archive] (.onion [archive]). The project also maintains related software such as cryptographic libraries on GitHub.
Bitcoin Wallet Recommendation
It is impossible to provide a blanket recommendation regarding which Bitcoin wallet to use. This is an individual decision that depends upon:
- technical skill
- personal risk assignment
- financial value in Bitcoin
- available time
- various other factors
Other bitcoin wallets like Electrum may have better usability, but they also come with their own issues; see Electrum Warnings for example. Despite Bitcoin Core limitations it should be seriously considered for security reasons because it is the official Bitcoin client, particularly if transacting with Bitcoin accounts of significant financial value. Relative strengths include:
- developed by the Bitcoin Core development team
- most peer reviewed
- most conservative, security-focused development
- reproducible builds 
- full validating node
- transactions are validated against the complete blockchain - this lowers the probability of servers 'lying' to the client (the client has a higher probability of seeing its true Bitcoin balance)
- higher privacy
- all blocks are downloaded - the locally running node will not tell servers which wallet addresses belong to the node
Unfortunately, it takes a very long time to download and verify the blockchain. A large amount of disk space is also required, which may or may not be more manageable by using Bitcoin pruning mode.
Bitcoin Core Usability
Compared to Electrum, some things are more difficult in Bitcoin Core such as:
- Simple backups - unfortunately Bitcoin Core does not support mnemonic phrase backup.
- Wallet configuration - it is not easy to set up a split offline wallet (cold storage) and online watch only wallet.
Bitcoin Core Setup
Perform these steps inside Whonix-Workstation ™ (Qubes-Whonix ™:
anon-whonix App Qube).
Enable Stream Isolation
Add a bitcoin-qt Start Menu Entry
Perform the following steps to create a
bitcoin-qt start menu entry; this procedure is optional.
Perform these steps to automatically start
bitcoin-qt; this step is optional.
Start from Command Line
bitcoin-qt (part of Bitcoin Core) from the command line, run.
Creating a Watch-Only Wallet
- Import address.
address with the actual address to be watched.
After installing a Bitcoin client, please consider making a donation to Whonix ™ to help keep it running for many years to come.
Donate Bitcoin (BTC) to Whonix ™.
- https://bitcoincore.org/en/about [archive]
https://bitcoinbinary.org/ [archive]- a repository of Reproducible Build Proofs for Bitcoin Projects.
- Non-Endorsement: these links have not been audited by Whonix ™, but are worthy of further investigation:
- Minor changes in the output such as new uids (email addresses) or newer expiration dates are inconsequential.
To avoid the following confusing output.
sha256sum --check --ignore-missing SHA256SUMS.asc bitcoin-0.21.1-x86_64-linux-gnu.tar.gz: OK sha256sum: WARNING: 20 lines are improperly formatted
- Because then Bitcoin Core cannot connect using transparent proxying anyhow.
- Perhaps as part of the ElectrumX instructions.