Bitcoin is a peer-to-peer network that uses public key cryptography and proof-of-work to securely record transactions in a distributed ledger called the blockchain without the need for a central authority. Users can send bitcoins to each other by digitally signing transaction messages that get broadcast to the network and recorded in the blockchain after validation by nodes in the network. The blockchain prevents double spending by ensuring that inputs are not spent more than once through a consensus mechanism involving proof-of-work.

1. What is Bitcoin?
Currency
Network

2. Bitcoins don’t exist
The Blockchain does

3. What is Bitcoin?
P2P network
Public Key cryptography
Proof of Work (hashing)

4. Alice Bob
Tim
“I give 1 BTC to Bob”
“I give you 1 BTC”
“She gave you 1 BTC”

5. Input A
Input B
Output A
Output B
Output C
0.5 BTC
1.0 BTC
0.7 BTC
0.4 BTC
0.4 BTC

6. inputs: [],
outputs: []
( )Alice signs
Alice broadcasts the Transaction (TX)
Other nodes check if the TX is valid

7. Quantity is not a solution
It needs to be hard to scale
for a single person
= Calculating power.

8. The problem must
- have a dynamic difficulty
- be checked by nodes in a
fraction of seconds

9. SHA256!
(or every hashing functions)
Find x so sha256(x).startsWith(0)
Find x so sha256(x).startsWith(00000)
Find x so sha256(x + block).startsWith(00000)

10. Input A DATA
Fee
0.0001 BTC
0.0001 BTC
Everything can be exchanged/stored

11. Multisig
Alice
Bob
Tim3a92..

12. Sidechains

13. Turing-complete
blockchains
IF this THEN something BELONGS TO someone
If Bob receives 1 BTC from Alice
Alice owns Bob’s computer
If Alice receives 1 BTC from Bob && today - tx.date > 30
Bob owns Alice’s computer

14. Potential for open data
Bank
Dev

15. Thanks
@LouisonDumont