Bank Management System

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   / \|_   _|  \/  |
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 / ___ \| | | |  | |
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Bank Management System

A terminal-based ATM application written in C

A fully-featured, multi-user banking terminal application with a rich TUI, salted password hashing, embedded SQLite persistence, real-time inter-user notifications via POSIX named FIFOs, and a thread-safe asynchronous notification engine.

Features

Category	Details
Authentication	User registration & login with salted SHA-256 password hashing
Account Management	Create, view, update, and delete bank accounts
Transactions	Deposits and withdrawals with overdraft protection
Ownership Transfer	Transfer any account to another registered user
Real-time Notifications	Recipient is notified instantly when an account is transferred to them
Multi-account Support	Each user can hold unlimited accounts across all types
Interest Projections	Live interest calculations displayed per account type
Input Validation	All user input is validated client-side with contextual error messages
Persistent Storage	All data survives restarts via an embedded SQLite3 database
Rich TUI	Full-colour ncurses interface with modal dialogs, scrollable menus, and live status bars

Screenshots

┌──────────────────────────────────────────────────────────────┐
│                    BANK MANAGEMENT SYSTEM                     │  ← Header bar
├──────────────────────────────────────────────────────────────┤
│                                                              │
│        _  _____ __  __                                       │
│       / \|_   _|  \/  |                                      │
│      / _ \ | | | |\/| |       ATM ASCII logo                 │
│     / ___ \| | | |  | |                                      │
│    /_/   \_|_| |_|  |_|                                      │
│                                                              │
│          B A N K   M A N A G E M E N T   S Y S T E M        │
│                                                              │
│   ┌─────────────── WELCOME ──────────────────┐              │
│   │  > Login                                 │              │
│   │    Register                              │              │
│   │    Exit                                  │              │
│   └──────────────────────────────────────────┘              │
├──────────────────────────────────────────────────────────────┤
│  Up/Down or 1-3 to navigate   ENTER to select               │  ← Footer bar
└──────────────────────────────────────────────────────────────┘

┌──────────────────────┐   ┌─────────────── OVERVIEW ──────────┐
│  ── MAIN MENU ──     │   │                                   │
│  > 1  Create Account │   │  Welcome back,                    │
│    2  Update Account │   │    Alice                          │
│    3  Check Details  │   │  ─────────────────────────────    │
│    4  View All       │   │  Accounts     : 3                 │
│    5  Transaction    │   │  Total Balance: $12,450.00        │
│    6  Remove Account │   │  ─────────────────────────────    │
│    7  Transfer       │   │  Monday, 23 Feb 2026              │
│    8  Exit           │   │  14:32                            │
└──────────────────────┘   └───────────────────────────────────┘

Architecture

The application is structured into four horizontal layers with clean separation of concerns:

┌─────────────────────────────────────────────────────┐
│               PRESENTATION LAYER                    │
│   tui.c · main_menu.c · init_menu.c · ui_helper.c  │
├─────────────────────────────────────────────────────┤
│              BUSINESS LOGIC LAYER                   │
│                    system.c                         │
├────────────────────────┬────────────────────────────┤
│   AUTHENTICATION       │      VALIDATION            │
│   auth.c · init_menu.c │   validators.c             │
│                        │   get_valid_*.c            │
├────────────────────────┴────────────────────────────┤
│               PERSISTENCE LAYER                     │
│         database.c · database_oper.c                │
├─────────────────────────────────────────────────────┤
│                UTILITIES LAYER                      │
│  hashing_utils.c · ipc_utils.c · string_utils.c    │
│  file_utils.c · terminal_utils.c                   │
└─────────────────────────────────────────────────────┘

Startup Sequence

main()
 ├── initialize_database("./data/atm.db")   # Create tables if absent
 ├── tui_init()                             # Start ncurses
 ├── initMenu(&u)                           # Login / Register screen
 │    └── getUserById()                     # Hydrate struct User from DB
 ├── pthread_create(notificationListener)  # Spawn FIFO listener thread
 └── mainMenu(u)                            # Enter main event loop
      └── [user selects operation]
           └── system.c function → DB → modal → success()

Project Structure

.
├── main.c                      # Entry point — initialisation & thread management
├── header.h                    # Shared struct definitions (User, Record, Date)
├── auth.c / auth.h             # Authentication helpers (getPassword, isUsernameTaken)
├── init_menu.c                 # Active login & registration TUI screen
├── main_menu.c                 # Main navigation menu with account overview panel
├── system.c                    # All six banking operations
├── ui_helper.c                 # success() and stayOrReturn() flow helpers
│
├── ui/
│   ├── tui.c                   # Full ncurses TUI engine (modals, input, layout)
│   └── tui.h                   # TUI public API
│
├── utils/
│   ├── hashing_utils.c / .h    # Salt generation, SHA-256 hashing, verification
│   ├── ipc_utils.c / .h        # POSIX FIFO creation, notification send/receive
│   ├── string_utils.c / .h     # String helpers (toLower)
│   ├── file_utils.c / .h       # Legacy flat-file record I/O
│   └── terminal_utils.c / .h   # getch() implementation (non-ncurses contexts)
│
├── validation/
│   ├── validators.c / .h       # Pure I/O-free validator functions
│   ├── get_valid_account.c     # Account number & type input loop
│   ├── get_valid_amount.c      # Monetary amount input loop
│   ├── get_valid_country.c     # Country lookup with ISO code support
│   ├── get_valid_date.c        # Date input with today-as-default
│   └── get_valid_phone.c       # Phone number input loop
│
├── database/
│   ├── database.c / .h         # Schema initialisation (CREATE TABLE IF NOT EXISTS)
│   └── database_oper.c         # Connection open/close helpers
│
└── data/
    ├── atm.db                  # SQLite database (auto-created on first run)
    └── countries.txt           # Country name / ISO code lookup table

Prerequisites

Linux (Ubuntu / Debian)

sudo apt update
sudo apt install -y \
    build-essential \
    libsqlite3-dev \
    libncurses-dev \
    libssl-dev

pthread is included with glibc — no separate package is needed.

macOS (Homebrew)

brew install sqlite ncurses openssl

# Make headers discoverable by the compiler
export CFLAGS="-I$(brew --prefix)/include"
export LDFLAGS="-L$(brew --prefix)/lib"

Arch Linux

sudo pacman -S base-devel sqlite ncurses openssl

Building

Using Make (recommended)

# Clone the repository
git clone https://github.com/<your-username>/bank-management-system.git
cd bank-management-system

# Create the data directory
mkdir -p data

# Build
make

# Binary is placed at ./atm

Manual GCC Command

gcc -Wall -Wextra -g -std=c11 \
    main.c auth.c system.c init_menu.c main_menu.c ui_helper.c \
    ui/tui.c \
    utils/hashing_utils.c utils/ipc_utils.c utils/terminal_utils.c \
    utils/string_utils.c utils/file_utils.c \
    validation/validators.c validation/get_valid_account.c \
    validation/get_valid_amount.c validation/get_valid_country.c \
    validation/get_valid_date.c validation/get_valid_phone.c \
    database/database.c database/database_oper.c \
    -o atm \
    -lsqlite3 -lncurses -lmenu -lpthread -lssl -lcrypto

Clean Build

make clean      # Remove object files and binary
make clean all  # Full rebuild from scratch

Running

Important: Always launch the binary from the project root directory. The application resolves ./data/atm.db and data/countries.txt relative to your working directory.

# From the project root:
./atm

The database (data/atm.db) is created automatically on the first run. No manual setup is required.

Usage Guide

First Run — Register an Account

At the welcome screen, select Register
Enter a username (letters a-z / A-Z only)
Enter a password (8–12 alphanumeric characters, confirmed by re-entry)
Select Login and enter your credentials

Creating a Bank Account

From the main menu, choose Create New Account
Fill in all fields in sequence:
- Account Number — a positive integer unique to your profile
- Date — MM/DD/YYYY, or press Enter to use today's date
- Country — full name, 2-letter ISO (US) or 3-letter ISO (DEU)
- Phone — 8 to 10 digits
- Initial Deposit — positive amount, up to 2 decimal places
- Account Type — select from the type menu (see Account Types)

Making a Transaction

Select Make a Transaction
Pick an account from the scrollable list
Choose Deposit or Withdrawal
Enter the amount

Fixed-term accounts (fixed01, fixed02, fixed03) are locked for the full term — transactions are blocked until maturity.

Transferring Account Ownership

Select Transfer Ownership
Pick the account you want to transfer
Enter the recipient's username
Confirm the transfer

The recipient will see a real-time notification modal the next time their tui_getch() loop polls — within 300 ms if they are actively using the application.

Navigation

Key	Action
`↑` / `↓` or `j` / `k`	Move selection
`Enter`	Confirm selection
`1`–`9`	Jump directly to item
`Esc` or `q`	Cancel / go back
`Y` / `N`	Yes / No in confirm dialogs
`←` / `→`	Toggle Yes/No in confirm dialogs

Security Model

Password Storage

Passwords are never stored in plain text. The storage format is:

<salt_hex>$<hash_hex>

Component	Detail
Salt	16 bytes of cryptographically random data via `RAND_bytes()` (OpenSSL CSPRNG)
Hash	SHA-256 of `password ‖ salt` using the OpenSSL EVP API
Encoding	Both components stored as lowercase hexadecimal strings
Separator	`$` character — the salt is always the first 32 hex chars

SQL Injection Prevention

Every database query uses parameterised statements (sqlite3_prepare_v2 + sqlite3_bind_*). There is no string concatenation into SQL anywhere in the codebase, making SQL injection architecturally impossible.

Input Masking

Password fields in the TUI render each character as * via the password flag in tui_input(). The raw password string is never written to any log file or the database.

Database Schema

CREATE TABLE users (
    id       INTEGER PRIMARY KEY AUTOINCREMENT,
    name     TEXT    NOT NULL,
    password TEXT    NOT NULL   -- format: salt_hex$hash_hex
);

CREATE TABLE accounts (
    id            INTEGER PRIMARY KEY AUTOINCREMENT,
    user_id       INTEGER NOT NULL,          -- FK → users.id
    account_id    INTEGER NOT NULL,          -- user-chosen number
    creation_date TEXT    NOT NULL,          -- ISO 8601: YYYY-MM-DD
    country       TEXT,
    phone         TEXT,
    balance       REAL    DEFAULT 0.0,
    account_type  TEXT,                      -- see account types below
    FOREIGN KEY (user_id) REFERENCES users(id)
);

The schema is initialised with CREATE TABLE IF NOT EXISTS on every startup, making the first-run setup fully automatic and subsequent runs a no-op.

Account Types & Interest

Type	Rate	Term	Interest Calculation
`savings`	7% / year	Rolling	`balance × 0.07 ÷ 12` paid monthly on the deposit day
`current`	0%	N/A	No interest
`fixed01`	4% / year	1 year	`balance × 0.04 × 1` paid at maturity
`fixed02`	5% / year	2 years	`balance × 0.05 × 2` paid at maturity
`fixed03`	8% / year	3 years	`balance × 0.08 × 3` paid at maturity

Interest projections are displayed live in the Check Account Details screen. Fixed-term accounts block all deposits and withdrawals for the duration of the term.

IPC Notification System

The application implements a real-time inter-user notification system using POSIX named FIFOs.

How It Works

Sender (transferOwnership)          Recipient (logged-in session)
─────────────────────────           ──────────────────────────────
notifyUser("alice", msg)            notificationListener thread
  └── open(/tmp/atm_fifo_alice,       └── read() polls every 1s
          O_WRONLY|O_NONBLOCK)            └── tui_set_notification(msg)
      └── write(msg)                          └── mutex write to
                                                  g_pending_notif[]

                                    Main thread (tui_getch)
                                      └── wtimeout(win, 300ms)
                                          └── polls g_pending_notif
                                              └── tui_modal_notification()
                                                  shows modal, waits
                                                  for keypress, flushes
                                                  input both sides

Thread Safety

The notification thread never calls any ncurses function. It only writes to a pthread_mutex_t-protected global string buffer. The main thread polls this buffer every 300 ms via wtimeout() — the only correct approach, since ncurses is single-threaded by design.

The previous approach of calling ungetch(KEY_F(12)) from a background thread was removed: ungetch is not thread-safe and caused corrupted input or dropped notifications.

FIFO Locations

/tmp/atm_fifo_<username_lowercase>

FIFOs are created on login and persist across sessions. The writer uses O_NONBLOCK so a transfer to an offline user never stalls the sender.

Module Reference

File	Exports	Description
`main.c`	`main()`	Subsystem init, thread lifecycle
`auth.c`	`getPassword()`, `isUsernameTaken()`	DB-backed credential helpers
`init_menu.c`	`initMenu()`, `getUserById()`	ncurses login/register screens
`main_menu.c`	`mainMenu()`	Navigation event loop with overview panel
`system.c`	`createNewAcc()` … `transferOwnership()`	All banking operations
`ui_helper.c`	`success()`, `stayOrReturn()`	Post-operation flow control
`ui/tui.c`	Full TUI API	ncurses engine: modals, input, layout, notifications
`utils/hashing_utils.c`	`generateSalt()`, `hashPassword()`, `verifyPassword()`	OpenSSL EVP password security
`utils/ipc_utils.c`	`createUserPipe()`, `notifyUser()`, `notificationListener()`	POSIX FIFO IPC
`validation/validators.c`	`val_*()` functions	Pure, I/O-free input validators
`database/database.c`	`initialize_database()`	Idempotent schema initialisation

Contributing

Contributions are welcome. Please follow the conventions already established in the codebase.

Code Style

Naming: snake_case for local variables, camelCase for public functions, _camelCase for static private functions, ALL_CAPS for macros
Headers: every .c file that exposes a public API has a matching .h with an include guard
Validators: new validators go in validation/validators.c / .h and must follow the int val_*(const char *input, ..., char err_out[VALIDATOR_ERR_BUF]) contract — no I/O, no side effects
Database: all queries must use parameterised statements — no string concatenation into SQL

Pull Request Process

Fork the repository and create a feature branch: git checkout -b feature/my-feature
Build with make clean all and confirm zero warnings under -Wall -Wextra
Run under valgrind --leak-check=full ./atm and confirm no memory errors
Open a pull request with a clear description of what changed and why

License

This project is licensed under the MIT License.

MIT License

Copyright (c) 2026

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Built with C · ncurses · SQLite3 · OpenSSL · pthreads

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data		data
src		src
Makefile		Makefile
README.md		README.md
atm		atm
audit_report.pdf		audit_report.pdf
audit_report.pdf:Zone.Identifier		audit_report.pdf:Zone.Identifier
c_programming_guide.pdf		c_programming_guide.pdf
c_programming_guide.pdf:Zone.Identifier		c_programming_guide.pdf:Zone.Identifier

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Bank Management System

Table of Contents

Features

Screenshots

Architecture

Startup Sequence

Project Structure

Prerequisites

Linux (Ubuntu / Debian)

macOS (Homebrew)

Arch Linux

Building

Using Make (recommended)

Manual GCC Command

Clean Build

Running

Usage Guide

First Run — Register an Account

Creating a Bank Account

Making a Transaction

Transferring Account Ownership

Navigation

Security Model

Password Storage

SQL Injection Prevention

Input Masking

Database Schema

Account Types & Interest

IPC Notification System

How It Works

Thread Safety

FIFO Locations

Module Reference

Contributing

Code Style

Pull Request Process

License

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