Adding taptree_of_horror example.

Adding bitcoin_hashes as dev dependency.

Cargo.toml

@@ -66,6 +66,11 @@ required-features = ["std", "base64"]
 name = "big"
 required-features = ["std", "base64", "compiler"]
 
+[[example]]
+name = "taptree_of_horror"
+path = "examples/taptree_of_horror/taptree_of_horror.rs"
+required-features = ["compiler"]
+
 [workspace]
 members = ["fuzz"]
 exclude = ["embedded", "bitcoind-tests"]

examples/taptree_of_horror/README.md

@@ -0,0 +1,20 @@
+# Taptree of Horror Example
+
+### Running this example:
+- `cargo run --example taptree_of_horror --features "compiler"`
+
+### Originally based on the TABConf 6, CTB.
+The challenge can be found here:
+- https://tabctb.com/six
+- https://tabctb.com/six/thebeginning/thetree/grim/iacceptyourterms.html
+
+### This example demonstrates:
+- Providing multiple extended private key (xpriv) descriptors for sample personas.
+- Creating a policy using logical 'and/or' conditions with preimages and signatures and timelocks.
+- Structuring a Taproot tree (taptree) with an internal key into logical branches and leaves based on the policy.
+- Implementing nine complex tapleaves within the taptree.
+- Building a spending transaction that signs and satisfies one of the tapleaves using signatures, preimages and a timelock.
+
+### Helpful Graphic to visualize using Excalidraw
+![taptree_of_horror](./taptree_of_horror.png)
+

examples/taptree_of_horror/helper_fns.rs

@@ -0,0 +1,59 @@
+use std::str::FromStr;
+
+use bitcoin::bip32::{DerivationPath, Xpriv};
+use bitcoin::hashes::{ripemd160, sha256, Hash};
+use miniscript::descriptor::DescriptorSecretKey;
+use miniscript::ToPublicKey;
+use secp256k1::Secp256k1;
+
+use crate::KEYS_PER_PERSONA;
+
+pub fn produce_grim_hash(secret: &str) -> (sha256::Hash, ripemd160::Hash) {
+    let mut hash_holder = sha256::Hash::hash(secret.as_bytes());
+    for _i in 0..5 {
+        hash_holder = sha256::Hash::hash(hash_holder.as_byte_array());
+        //println!("{} hash: {}", i, hash_holder);
+    }
+
+    let ripemd_160_final = ripemd160::Hash::hash(hash_holder.as_byte_array());
+    (hash_holder, ripemd_160_final)
+}
+
+pub fn produce_kelly_hash(secret: &str) -> (sha256::Hash, sha256::Hash) {
+    let prepreimage = secret.as_bytes();
+    let preimage_256_hash = sha256::Hash::hash(prepreimage);
+    let result256_final = sha256::Hash::hash(&preimage_256_hash.to_byte_array());
+    (preimage_256_hash, result256_final)
+}
+
+pub fn produce_key_pairs(
+    desc: DescriptorSecretKey,
+    secp: &Secp256k1<secp256k1::All>,
+    derivation_without_index: &str,
+    _alias: &str,
+) -> (Vec<bitcoin::PublicKey>, Vec<Xpriv>) {
+    let mut pks = Vec::new();
+    let mut prvs = Vec::new();
+
+    let xprv = match &desc {
+        DescriptorSecretKey::XPrv(xpriv) => xpriv,
+        _ => panic!("not an xpriv"),
+    };
+
+    for i in 0..KEYS_PER_PERSONA {
+        let pk = desc
+            .to_public(secp)
+            .unwrap()
+            .at_derivation_index(i.try_into().unwrap())
+            .unwrap()
+            .to_public_key();
+
+        let derivation_with_index = format!("{}/{}", derivation_without_index, i);
+        let derivation_path = DerivationPath::from_str(&derivation_with_index).unwrap();
+        let derived_xpriv: Xpriv = xprv.xkey.derive_priv(secp, &derivation_path).unwrap();
+
+        pks.push(pk);
+        prvs.push(derived_xpriv);
+    }
+    (pks, prvs)
+}