leo/examples/broken_bank/README.md

# Broken Bank

A "broken" bank written in Leo.

## Summary

This application implements a bank that issues tokens to users and allows users to deposit tokens and accrue interest on their deposits.


### User Flow
1. The bank issues users tokens via the `issue` function.
2. A user deposits tokens via the `deposit` function.
3. Upon a user's request to withdraw, the bank calculates the appropriate amount of compound interest and pays the user the principal and interest via the `withdraw` function.

Note that the program can be easily extended to include addition features such as a `transfer` function, which would allow users to transfer tokens to other users.

## Bugs

You may have already guessed that this program has a few bugs. We list some of them below: 
- `withdraw` can only be invoked by the bank. A malicious bank could lock users' tokens by not invoking `withdraw`.
- `withdraw` fails if the sum of the interest and principal is greater than the user's balance. 
- User's can increase their principal by depositing tokens multiple times, including immediately before withdrawl.
- Integer division rounds down; if the calculated interest is too small, then it will be rounded down to zero.

Can you find any others?

## Language Features and Concepts
- `record` declarations
- `console.assert_eq`
- core functions, e.g. `BHP256::hash`
- record ownership
- loops and bounded iteration
- mappings
- finalize

## Running the Program

Leo provides users with a command line interface for compiling and running Leo programs.
Users may either specify input values via the command line or provide an input file in `inputs/`.

### Configuring Accounts
The `program.json` file contains a private key and address.
This is the account that will be used to sign transactions and is checked for record ownership.
When executing programs as different parties, be sure to set the `private_key` and `address` fields in `program.json` to the appropriate values.


See `./run.sh` for an example of how to run the program as different parties.


The [Aleo SDK](https://github.com/AleoHQ/leo/tree/testnet3) provides a command line interface for generating new accounts.
To generate a new account, run
```
leo account new
```


### Providing inputs via the command line.
1. Run
```bash
leo run <function_name> <input_1> <input_2> ...
```
See `./run.sh` for an example.


### Using an input file.
1. Modify `inputs/auction.in` with the desired inputs.
2. Run
```bash
leo run <function_name>
```
For example,
```bash
leo run issue
leo run deposit
leo run withdraw
```