Electronic Cheque Payment System

Peer-to-Peer / Client-Server Payment Platform (Spring Boot + PostgreSQL)

This project implements a secure, peer-to-peer electronic cheque payment system designed for mobile and web use

The system supports cheque issuance, transfer (QR / Email), clearing, settlement, encryption, digital signatures, and full audit logging

Tech Stack

Backend (Java)

• Spring Boot 3
• Spring Web (REST API)
• Spring Security (JWT authentication)
• Spring Data JPA + Hibernate
• PostgreSQL
• Lombok
• Java Cryptography (AES-GCM, RSA-OAEP, SHA-256)
• Spring AOP (Audit Logging)

Infrastructure

• PostgreSQL (local or cloud)
• Optional: ELK Stack (ElasticSearch + Logstash + Kibana)

System Architecture Overview

 ┌──────────────────┐       ┌───────────────────────┐
 │    Frontend      │ <---> │   Spring Boot API     │
 │   Javascript     │       │  Authentication       │
 └──────────────────┘       │  Cheque Management    │
                            │  Transfer (QR/Email)  │
                            │  Clearing & Settlement│
                            │  Encryption Module    │
                            │  Audit Logging        │
                            └──────────┬────────────┘
                                       │
                            ┌──────────▼───────────┐
                            │     PostgreSQL       │
                            │ Users / Cheques /    │
                            │ Accounts / AuditLogs │
                            └──────────────────────┘

Core Features

1. Authentication & User Management Module

• Register (username, email, real name, phone number)
• Login (JWT)
• Profile management
• Logout
• Validation rules (name <25 chars, phone <15 digits)

2. Cheque Management Module

• Issue cheque (with AES + RSA encryption + signature)
• Query cheque by ID or status
• Update cheque status (CLEARED / VOIDED / EXPIRED / SPLIT)
• Fragment cheque into smaller child cheques
  • Child cheques cannot be split again
  • Split amount total must equal parent cheque amount

3. Cheque Transfer Module

Supports three delivery methods:

• Email Transfer (Spring Mail + SMTP provider, e.g., SendGrid / Outlook)
• QR Code Transfer (Generates Base64 PNG encoded QR containing encrypted cheque payload)

4. Security & Encryption Module

• AES-GCM (Symmetric Encryption)

  • Used to encrypt cheque payloads
  • GCM provides built-in tamper detection and integrity via authenticated encryption
  • Each cheque payload includes : amount, payerRealName, payerUsername, payeeUsername, expiryDate, nonce

• RSA-2048 (Asymmetric Encryption)

  • AES key is encrypted using RSA-OAEP with SHA-256 padding
  • Only the server holding the RSA private key can decrypt the AES key
  • Provides confidentiality even if the cheque is transmitted via Email and QR Code

• Digital Signature (SHA-256 + RSA)

  • Each cheque is signed using the RSA private key : Sign( SHA-256(chequeData) )
  • During clearing, the system performs :
    1. Decrypt AES key → decrypt cheque payload
    2. Re-build the original cheque JSON
    3. Verify signature using RSA public key
  • If either signature or AES integrity tag fails → the cheque is rejected

• JWT Authentication
  Used for login, profile fetching, and access control for cheque APIs

• Password Hashing (BCrypt)
  All passwords hashed using BCrypt with salt and cost factor

• Replay-Attack Protection
  Each cheque contains a unique nonce:

  • Stored inside encrypted cheque payload
  • Saved to database only after settlement
  • Checked during verification

5. Clearing & Settlement Module

• Verify encryption
• Decrypt AES key using RSA private key
• Decrypt cheque data
• Verify signature
• Check expiry date and replay nonce
• Settle → update account balance and mark nonce as used
• Scheduled batch settlement (Spring Scheduler)

6. Audit & Logging Module

• Spring AOP intercepts all controller calls
• Logs success / failure / security events
• Sensitive data (passwords, emails, phone numbers) masked
• Logs stored in DB + Logback file
• Supports ELK integration for visualization

Project Structure (Backend)

src/main/java/com/chequepay
 ├── audit/         # Audit logs, AOP aspects, masking utilities
 ├── config/        # Spring Security, JWT config, CORS, App configs
 ├── controller/    # REST controllers (Auth, Cheque, Transfer, Clearing)
 ├── dto/           # Request & Response DTOs
 ├── entity/        # JPA entities (User, Cheque, Account, AuditLog)
 ├── repository/    # Spring Data JPA Repositories
 ├── service/       # Core business logic (Auth, Cheque, Transfer, Clearing)
 ├── util/          # Crypto utilities (AES, RSA), signatures, nonce, etc.
 └── ChequePayApplication.java

API Examples

User APIs

• POST /auth/register
• POST /auth/login
• GET /auth/profile
• POST /auth/logout
• GET /account/balance

Cheque APIs

• POST /cheques
• GET /cheques/{id}
• PATCH /cheques/{id}/status
• POST /cheques/{id}/split

Transfer APIs

• POST /transfer/email?chequeId={id}
• POST /transfer/qr?chequeId={id}

Clearing APIs

• POST /clearing/verify?chequeId={id}
• POST /clearing/settle?chequeId={id}

Running the Project

1. Configure application.yaml

spring:
  datasource:
    url: jdbc:postgresql://localhost:5432/cheque-pay
    username: postgres
    password: yourpassword

2. Start Backend

mvn spring-boot:run

3. Start Frontend

npm install
npm run dev

Future Enhancements

• Multi-signature cheques
• Blockchain-based cheque lineage
• Push notification on cheque received
• QR offline verification

Purpose of This Project

This system is designed for academic research, demonstrating:

• Secure P2P payment architecture
• Cryptographic cheque verification
• Anti-tampering & anti-replay mechanisms
• Digital settlement workflow
• Best-practice logging & system observability