Blockchain 2026 — Labs

Course code for the IPv8 labs.

Setup

pip install -r requirements.txt

Each lab uses an IPv8 .pem key file. Labs 2 and 3 reuse the key each member registered in Lab 1.

Lab 2 — Coordinated Group Signing over IPv8

3-person group signs 3 challenge nonces from the server within a 10-second wall-clock budget. Each round must be submitted by a different member.

Files

• assignment2/part1.py — one-time group registration. Sends the 3 member pubkeys (in canonical order) to the server and prints the returned group_id.
• assignment2/part2.py — the timed signing client. Round-robin: member 1 submits round 1, member 2 round 2, member 3 round 3. Each member runs the same script with their own .pem.

Running

Part 1 (one person):

cd assignment2
python part1.py

Wait for Response: success=True, group_id=.... Save the group_id, then Ctrl+C.

Part 2 (all 3 teammates):

Each teammate fills in their own MY_KEY_FILE and pastes the shared GROUP_ID + 3 member pubkeys, then runs:

cd assignment2
python part2.py

Each script discovers the other 2 + the server, does a Ready handshake, then member 1 fires round 1. The chain auto-progresses through all 3 rounds via RoundDone messages.

Notes

• Uses the same .pem from Lab 1.
• Intra-team messages have retransmission tasks to handle UDP packet loss within the 10s budget.
• All 3 members must hardcode the 3 pubkeys in the same canonical order; this order also determines which round each member submits.

Lab 3 — PoW Blockchain over IPv8

3-node Proof-of-Work blockchain. Each member runs one node; nodes mine, propagate, and converge on a single chain. After registration, the server joins the blockchain community, submits a test transaction, and verifies the chain across all 3 nodes.

Files

• assignment3/part1.py — one-time registration. Sends the group_id + the self-chosen blockchain community ID to the server so it knows which community to join.
• assignment3/chain.py — chain primitives: block header packing (84 bytes), block_hash, tx_hash, txs_hash body commitment, PoW search, genesis block, and serialize_txs/deserialize_txs for sending transactions.
• assignment3/node.py — BlockChain class. Owns the blocks list, mempool, mining (prepare_next), validation, append, and fork-switch logic.
• assignment3/community.py — the IPv8 node. Server-facing handlers, block propagation between teammates, and the mining loop.

Running

Part 1 (one person):

cd assignment3
python part1.py

Wait for Response: success=True, message=.... Then Ctrl+C.

Part 2 (all 3 teammates):

Each teammate fills in their own MY_KEY_FILE, then runs:

cd assignment3
python community.py

Each node joins the blockchain community, discovers the others, and starts mining. The server queries the nodes in the background; pass confirmation can be seen when running part1.py again after a good-looking run.

Tests

Unit tests for the chain primitives and single-node mining + validation live in assignment3/tests/. Run them with pytest from a virtualenv:

cd assignment3
python3 -m venv .venv          # needs python3-venv (sudo apt install python3-venv)
source .venv/bin/activate
pip install pytest
pytest tests/

tests/conftest.py puts assignment3/ on sys.path so the tests import chain/node the same way the rest of the code does. Always run via pytest (not python3 tests/test_chain.py directly), otherwise the import path isn't set up.

Notes

• Uses the same .pem from Lab 1.
• Mining difficulty is set high enough (MINING_DIFFICULTY = 24) + a 3s sleep between blocks to keep propagation ahead of new blocks and prevent the 3 chains from diverging.
• Re-run part1.py to reset the server's retry counter (or if the blockchain community ID changes).
• All 3 members must hardcode the 3 pubkeys in the same canonical order.