Here’s What’s Next for Bitcoin Wallet GreenAddress After Being Acquired by Blockstream

Blockstream

announced the acquisition of Bitcoin wallet provider
GreenAddress

on Wednesday. In
a post

on the company’s official blog, Blockstream President
Adam Back

noted, “GreenAddress has a demonstrated track record of delivering
an industry-leading product that prioritizes security, privacy and
convenience.”

GreenAddress has been quick to implement new Bitcoin features,
such as
fee
estimation

and

replace-by-fee

, into its own wallet. Also, GreenAddress developer
Lawrence
Nahum

is a
supporter

of the
Bitcoin Core scalability roadmap

and says he’s excited about the improvements that are coming to
Bitcoin in the near future.

Bitcoin Magazine

reached out to Nahum to get the details on what GreenAddress will
be working on now that it is under the Blockstream umbrella of
Bitcoin products and services.

Implementing CHECKSEQUENCEVERIFY

Nahum was quick to bring up the upcoming implementation of
OP_CHECKSEQUENCYVERIFY

(
CSV

) to improve the refund process on their 2-of-2

multisignature addresses

.

One of the key features of GreenAddress is the ability to
complete what are essentially instant Bitcoin transactions. This
works by putting user funds in a 2-of-2 multisig address where the
two parties are the user and GreenAddress. If someone trusts
GreenAddress to not
double spend

a transaction, then he or she can trust this user’s GreenAddress
wallet to do the same.

A refund transaction is also pre-signed and held by the user to
prevent funds being locked up in an address that requires a
signature from GreenAddress to send a transaction. Currently, a
pre-signed

nLocktime

refund transaction is emailed to the user when a transaction is
received on a 2-of-2 address (including

change

transactions). This transaction becomes valid after a predetermined
amount of time.

With CSV, the refund process can be handled directly on the
blockchain. The gist of it is that a 2-of-2 multisignature address
will be controlled only by the user after a certain amount of time
has passed.

CSV also will get rid of a window of trust that is involved with
the current nLocktime process. This window of trust involves the
problem of an nLocktime transaction ID not being set in stone until
it is confirmed on the blockchain; this issue is known as
transaction malleability

.

Nahum noted that he wants to wait until
MAST

(Merkalized Abstract Syntax Tree) is available before implementing
CSV due to reasons related to user privacy.

“Once MAST is into play, you only see the 2-of-2,” he explained.
“You don’t see the [refund transaction] unless it is used, which
means you only reveal the nLocktime when you do recovery with
MAST.”

In other words, MAST would enable the same level of privacy for
these addresses as they enjoy today with the added benefit of
CSV.

Building a Bitcoin and Sidechains Wallet Library

In addition to working on its own wallet, the GreenAddress team
will also be working on a library that any developer will be able
to use.

“The library will help us deliver better and consistently to all
platforms without rewriting a lot of code for each platform,” said
Nahum.

The library is in C but it will have bindings to other major
languages such as Java and Python. Other C libraries, such as

libsecp256k1

, will also be reused in this new library from the GreenAddress
team.

“With the library, we do not want to reinvent the wheel,” added
Nahum. “But we do want C to support all platforms, so we are
reusing where applicable.”

Nahum explained that C was chosen as the language for the
library because it can work everywhere and it’s also easy to
interface with other popular languages. As an example provided by
Nahum,
bitcoinj

can be used on iOS with some frameworks, but running it on a
hardware wallet would be difficult.

According to Nahum, support for various features enabled in
Blockstream’s
Elements
Alpha

sidechain also will be supported in the library.

“So far, we have support for some of the features of Elements
Alpha and we want to complete support, plus add support for
features that will be released in the future (at least the ones
that are applicable to the wallet),” said Nahum. “We already added
support for
Confidential Transactions

in GreenAddress before
Scaling Bitcoin Hong Kong

as we were experimenting with the tech.”

“But our support was very proof-of-concept,” he said. “A lot
more work is needed to make our support more robust.”

“Our goal with the library is to make it easier for us and other
developers to build powerful, secure, and fast multi-platform
wallets for Bitcoin that support
sidechains

. I think this is good for the library as it makes it more modular
and it allows people to innovate more. It will also be a way to get
an early peek at features that could eventually come to
Bitcoin.”

Nahum would like the C library to work with Bitcoin mainnet, the
testnet and sidechains.

The Long-Term Vision for GreenAddress

Long term, the plan for GreenAddress is to provide its users
with a user-friendly, convenient wallet while also learning as
little about them as possible.

“Our ideal place is where we don’t know which transactions are
involved, yet we can validate the things users wants us to validate
such as
two-factor authentication

or spending limits,” explained Nahum. “The less data we have the
better.”

Nahum also shared his excitement for new improvements, such as
Schnorr signatures

, that should be added to Bitcoin in the near future.

“Schnorr is going to be great,” he said. “Finally,
multi-signature and single-signature transactions will cost the
same in fees and will look the same from outside. Plus, the
transaction will be smaller.

“With some of these improvements, we can not only improve
privacy and security but also ease-of-use, as there will be less
for users to keep track of (i.e. no nLocktime files) while having
better privacy and atomic security,” Nahum concluded.

While the Bitcoin Core wallet still has better privacy features,
GreenAddress offers unique protection against malware via
two-factor authentication.
GreenBits

, another wallet from the GreenAddress team, also allows users to
avoid trusting a third party by allowing them to connect to their
own
full
nodes

.

mm

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