Mast and Schnorr Signatures
Bitcoin’s development effort for the past few years has been focused on a few key concepts, privacy, scalability and efficiency. One of the first improvements was Segregated witness which is ushering in the rest, Lightning Network followed but was an effort in a different direction as it took transactions off-chain rather than optimizing the on-chain process. Some of the upcoming technologies aimed at optimizing this process are Schnorr Signatures and Merkelized Abstract Syntax Trees or MAST for short.
A BIP proposal for 'cancellable' transactions

Alejandro Ranchal Pedrosa and Tucci-Piergiovanni proposed a new BIP to extend OP_CSV1 and/or OP_CLTV2 to allow and interpret negative values.

The discussion that followed concluded that the BIP would be breaking a fundamental rule which is that valid transactions remain valid. This could lead to loss of funds when several transactions are made invalid.

Witness Serialization in PSBT Non-witness UTXOs

Pieter Wuille made some comments regarding the serialization of non-witness UTXOs in the recenlty proposed BIP174:

BIP174 currently specifies that non-witness UTXOs (the transactions being spent by non-witness inputs) should be serialized in network format.

I believe there are two issues with this.

PSBT (BIP 174) - Partially Signed Bitcoin Transactions

Multisig transactions 1 have been a great use case of Bitcoin for the past few years, they require unsigned or partially signed transactions to be passed between multiple parties to “co-sign” them. However, there is currently no unified format for how multiple parties may share these transactions between multiple signers, it depends on the particular implementation for each wallet making it hard to do among parties using different Bitcoin wallets.

A draft BIP (174), which was proposed last year by Andrew Chow, was recently a subject of interest among Bitcoin developers. It aims to create a standard extensible format that different clients can implement making Partially Signed Bitcoin Transactions (PSBT) easier to pass around users to sign and combine their signatures.

An Introduction to Segregated Witness ( Segwit )

If you’ve been around the cryptocurrency space in the last year or so, you had to notice the insane fees on Bitcoin around December and January. Bitcoin’s adoption has been growing along its price and so the amount of transactions done per day has been going up. There was a point where a day’s worth of transaction costs in USD reached 22 Million dollars. For perspective, it currently averages at 200 thousand dollars, that’s about 99% less.

Now while Bitcoin’s price and the cryptocurrency bear market had a toll on that, last year we saw a massive effort by the Bitcoin community to drive up the number of transactions per second the blockchain could handle. To achieve this goal two strategies were proposed, one of them was Bitcoin Core’s effort introducing SegWit, short for Segregated Witness, which was activated by a user activated soft fork (UASF), and the other was Bitcoin Cash’s user activated hard fork . To further explain this we need to touch on simple basic Bitcoin blockchain technical details.