Add pda text

README.md

@@ -2,7 +2,7 @@
 
 <br>
 
-### Our development resources, aiming to onboarding engineers to Solana development. From geeks to geeks.
+### Our development resources aim to onboard engineers to Solana development. From geeks to geeks.
 
 <br>
 

chapters/04_program_derived_addresses.md

@@ -2,3 +2,107 @@
 
 
 <br>
+
+### tl; dr
+
+<br>
+
+
+* PDAs are addresses with special properties. They are not public keys (so they don't have an associated public key).
+
+* PDAs provide a mechanism to build hashmap-like structures on-chain, allowing programs to sign instructions.
+
+* PDAs simplify the programming model and make programs more secure. 
+
+
+<br>
+
+----
+
+### PDA Creation
+
+<br>
+
+* PDA are created by hashing a number of seeds the user can choose with the `program_id`.
+
+* Seeds can be anything: pubkey, strings, an array of numbers, etc.
+
+* There is a 50% chance that this hash can result in a public key, so a bump has to be searched:
+
+<br>
+
+
+```rust
+// pseudo code
+fn find_pda(seeds, program_id) {
+  for bump in 0..256 {
+    let potential_pda = hash(seeds, bump, program_id);
+    if is_pubkey(potential_pda) {
+      continue;
+    }
+    return (potential_pda, bump);
+  }
+  panic!("Could not find pda after 256 tries.");
+}
+```
+
+<br>
+
+* The first bump that results in a PDA is called a "canonical bump," and they are the recommended one for usage.
+
+<br>
+
+---
+
+### Hashmap-like Structures with PDAs
+
+<br>
+
+* PDAs are hashed from a bump, a program_id, and several seeds. These seeds can be used to build hashmap-like structures on-chain.
+
+* With PDA, you can create structs that encode the information about a relationship between the user and some data account, so that PDA serves as the address:
+
+<br>
+
+```rust
+pub struct UserStats {
+  level: u16,
+  name: String,
+  bump: u8
+}
+```
+
+<br>
+
+
+----
+
+### CPI Signing with PDAs
+
+<br>
+
+
+* In some cases, it's possible to reduce the number of accounts needed by making a PDA storing state also sign a CPI instead of defining a separate PDA for that.
+
+* This means that programs can be given control over assets, which they then manage according to the rules defined in the code.
+
+<br>
+
+---
+
+### Demos
+
+<br>
+
+* Learn how PDA works on Anchor through [demo 3](https://github.com/urani-labs/solana-dev-onboarding-rs/tree/main/demos/03_anchor_pda).
+
+<br>
+
+---
+
+### References
+
+<br>
+
+* [Anchor Docs on PDA](https://www.anchor-lang.com/docs/pdas)
+