System requirements

Functional:

User Registration and Authentication:

• The system must support secure voter registration.
• Voters should authenticate using multi-factor authentication (MFA) before casting a vote.

Voter Eligibility Verification:

• Verify the voter’s eligibility based on pre-defined criteria such as age, citizenship, and residency.

Ballot Creation and Distribution:

• Admins should be able to create, distribute, and manage different types of ballots (e.g., local, state, national elections).

Vote Casting:

• Voters must be able to cast their votes securely and anonymously.
• The system should prevent multiple votes by the same voter for the same election.

Vote Storage:

• Votes must be securely stored with encryption to ensure they are tamper-proof.

Vote Tabulation:

• The system should automatically count and tabulate votes.
• Provide real-time vote counting and results display.

Auditability and Transparency:

• Provide a mechanism for independent audits without compromising voter anonymity.
• A verifiable trail of the entire voting process should be maintained.

Notification System:

• Notify voters about their registration status, upcoming elections, and successful vote casting.

Role Management:

• Admins should have different levels of access and permissions, such as creating ballots, monitoring results, and managing voter databases.

System Resilience:

• The system should support fault tolerance, load balancing, and disaster recovery to handle high traffic during peak voting periods.

Non-Functional:

Security:

• Implement encryption for data in transit and at rest.
• Utilize secure protocols (e.g., HTTPS, TLS) for all communications.
• Ensure robust protection against common cyber-attacks like DDoS, SQL injection, and phishing.

Scalability:

• The system must scale to accommodate up to 100 million voters for national elections.
• Support horizontal scaling with load balancing across multiple servers and regions.

Performance:

• The system should handle a high number of concurrent users (voters) with minimal latency.
• Ensure that vote casting and tabulation operations are executed within a few seconds.

Reliability:

• The system should have an uptime of at least 99.99% during election periods.
• Implement redundancy for all critical components to avoid single points of failure.

Privacy:

• Ensure that voter information and voting choices are kept confidential.
• Adhere to relevant privacy laws and regulations.

Compliance:

• The system must comply with all relevant electoral laws and regulations.
• Implement logging and monitoring to track compliance.

Usability:

• The voting system should be intuitive and user-friendly, accommodating voters of all technical skill levels.
• Provide accessibility features for voters with disabilities.

Auditability:

• Maintain detailed logs of all transactions and actions within the system for auditing purposes.
• Ensure that audit logs are immutable and can only be accessed by authorized personnel.

Capacity estimation

Assumptions

• Voter Turnout:
• Local Elections: 10,000 to 50,000 voters.
• Statewide Elections: 1 million to 5 million voters.
• National Elections: 10 million to 100 million voters.
• Peak Traffic:
• Assume peak traffic occurs in the last 2 hours of the voting period, with up to 50% of voters casting their votes during this time.
• Vote Storage:
• Each vote, including metadata (time, ballot type, voter ID), is approximately 1 KB.
• Concurrency:
• The system should handle up to 1 million concurrent users at peak times.

Capacity Requirements

Database Storage:

• Local Elections: 50,000 votes * 1 KB/vote = 50 MB.
• Statewide Elections: 5 million votes * 1 KB/vote = 5 GB.
• National Elections: 100 million votes * 1 KB/vote = 100 GB.

Considering historical data, logs, and redundancy, allocate at least 2x storage capacity.

Network Bandwidth:

• Local Elections: 50,000 votes in 2 hours (3600 seconds), ~14 votes/second.
• Statewide Elections: 5 million votes in 2 hours, ~694 votes/second.
• National Elections: 100 million votes in 2 hours, ~13,889 votes/second.

Assume average bandwidth of 1 KB per vote transmission.

• Local: 14 KB/s
• Statewide: 694 KB/s
• National: 13.89 MB/s

Server Capacity:

• Estimate the number of servers based on peak traffic and desired response time.
• Local Elections: 2-4 servers for redundancy.
• Statewide Elections: 10-20 servers with load balancing.
• National Elections: 100-200 servers distributed across regions.

Caching:

• Utilize caching for static content and results to reduce database load and latency.
• Implement a distributed cache for high availability and scalability.

API design

User Registration API

Authentication API

Ballot Retrieval API

Vote Casting API

Audit Log Retrieval API

Database design

Data Model Overview

To manage the voting system's data efficiently, the following key entities are identified:

1. Voters: Stores information about registered voters.
2. Elections: Defines different types of elections (local, state, national) and the associated metadata.
3. Ballots: Contains information about individual ballots associated with an election.
4. Candidates: Lists the candidates participating in an election.
5. Votes: Stores the votes cast by voters, ensuring the integrity and secrecy of the votes.
6. Audit Logs: Tracks actions within the system for audit and compliance purposes.

Database Considerations

1. Data Integrity: Foreign keys are used to enforce relationships between tables, ensuring that data remains consistent across the system.
2. Security: Sensitive data such as passwords and votes are stored encrypted, adhering to best security practices.
3. Performance: Indexes should be added on frequently queried fields such as voter_id, election_id, and candidate_id to improve query performance.

High-level design

Key Components

User Interface (UI) Layer:

• Web Application: A responsive web interface for voters and administrators. Voters can register, authenticate, retrieve ballots, and cast votes. Administrators can manage elections, monitor results, and perform audits.
• Mobile Application: A mobile app offering similar functionality to the web application for voters, ensuring accessibility across devices.

API Gateway:

• A centralized gateway that routes requests from the UI layer to appropriate backend services. It handles authentication, rate limiting, and request logging.

Authentication Service:

• Manages voter registration, login, and multi-factor authentication. Ensures secure access to the system.

Election Management Service:

• Responsible for creating and managing elections, including defining ballots, candidates, and election rules. Interfaces with the Ballot Distribution Service.

Ballot Distribution Service:

• Handles the distribution of ballots to eligible voters and ensures that each voter receives the correct ballot.

Voting Service:

• Manages the vote-casting process, ensuring that votes are securely stored and tabulated. This service ensures that each voter can cast only one vote per election and that votes are recorded anonymously.

Vote Storage & Tabulation Service:

• Stores encrypted votes and performs vote tabulation. It aggregates results in real-time and provides updates to authorized users.

Audit & Monitoring Service:

• Provides tools for auditing the election process, including access to audit logs and system monitoring dashboards. Ensures transparency and accountability.

Database Layer:

• A distributed, secure database that stores all data related to voters, elections, ballots, votes, and audit logs. Ensures high availability and data consistency.

Security Layer:

• Encompasses encryption, secure communication protocols, and intrusion detection systems to protect the system against threats and ensure voter privacy.

Load Balancer:

• Distributes incoming traffic across multiple instances of the application and services to ensure reliability and performance during peak voting periods.

Cache Layer:

• Uses a distributed cache to store frequently accessed data, such as election results, to reduce database load and improve response times.

Disaster Recovery & Backup:

• Implements backup strategies and disaster recovery plans to ensure data integrity and availability in case of failures.

Design Considerations

1. Modularity: Each service is designed as an independent module, allowing for easier maintenance, testing, and scaling.
2. Scalability: The system supports horizontal scaling at every layer, from the API Gateway to the Database Layer, to accommodate varying levels of voter turnout.
3. Security: The Security Layer is integrated across the system, ensuring end-to-end encryption, secure data storage, and robust authentication mechanisms.
4. Resilience: Load balancers, distributed databases, and disaster recovery plans are in place to ensure system availability during high-traffic periods and unforeseen failures.

Request flows

This flow illustrates how a new voter registers in the system.

Step-by-Step Process:

Voter Submits Registration Form:

• The voter fills out the registration form on the web or mobile application and submits it.

API Gateway Receives Request:

• The API Gateway routes the registration request to the Authentication Service.

Authentication Service Validates Data:

• The Authentication Service validates the registration data (e.g., ensuring the voter ID is unique, verifying the format of the email, etc.).

Authentication Service Creates Voter Record:

• Upon successful validation, the Authentication Service creates a new voter record in the Voters table within the database.

Confirmation Sent to Voter:

• The Authentication Service returns a success response to the API Gateway, which then relays this response to the voter via the web/mobile application.

Vote Casting Flow

This flow describes how a voter casts their vote securely.

Step-by-Step Process:

Voter Logs In:

• The voter logs into the system using their credentials and MFA, which is authenticated by the Authentication Service.

Voter Requests Ballot:

• The voter requests their ballot. The request is routed through the API Gateway to the Ballot Distribution Service.

Ballot Distribution Service Fetches Ballot:

• The Ballot Distribution Service retrieves the correct ballot for the voter from the database.

Voter Receives and Casts Ballot:

• The voter selects their preferred candidate and submits the vote.

Voting Service Records Vote:

• The Voting Service validates and encrypts the vote, then stores it in the Votes table in the database.

Confirmation Sent to Voter:

• The Voting Service sends a confirmation response through the API Gateway back to the voter.

Vote Tabulation Flow

This flow explains how the system tabulates votes and provides results to authorized users.

Step-by-Step Process:

Admin Logs In:

• The admin logs in to the system using their credentials, authenticated by the Authentication Service.

Admin Requests Vote Tabulation:

• The admin requests the current tabulation of votes for a specific election.

Vote Tabulation Service Processes Request:

• The Vote Storage & Tabulation Service retrieves and aggregates votes from the database.

Tabulated Results Sent to Admin:

• The aggregated results are sent back to the admin through the API Gateway.

Design Considerations

1. Consistency: The flow ensures that all operations are executed in a consistent order, maintaining data integrity.
2. Security: Each request flow is secured by authentication and encryption to protect voter privacy and system integrity.
3. Performance: The system is designed to handle high volumes of concurrent requests efficiently, with caching and load balancing mechanisms to reduce latency.

Detailed component design

Voting Service

Overview

The Voting Service is responsible for securely handling the vote-casting process. It ensures that each vote is valid, encrypted, and stored correctly, preventing multiple votes from the same voter for the same election. This service plays a crucial role in maintaining the integrity and secrecy of the voting process.

Internal Architecture

• Input Validation Module:
• Validates the incoming vote request, ensuring that the voter is eligible and that the vote has not already been cast for the given ballot.
• Encryption Module:
• Encrypts the vote using a strong encryption algorithm (e.g., AES-256). The encryption ensures that the vote content remains confidential even within the system's database.
• Vote Recording Module:
• Records the encrypted vote into the database. This module also ensures idempotency, meaning that if the same request is submitted multiple times, only one vote is recorded.
• Audit Logging Module:
• Logs the vote-casting action into the Audit Logs table, capturing relevant details without compromising voter anonymity.

Scalability Considerations

• Stateless Design:
• The Voting Service is stateless, meaning it does not retain any session information. This design choice allows it to scale horizontally, handling a large number of concurrent vote submissions by simply adding more instances behind the load balancer.
• Database Sharding:
• To handle millions of votes, the Vote table can be partitioned by election ID, allowing the system to distribute the storage and querying load across multiple database shards.
• Queue-based Processing:
• In high-traffic situations, votes can be temporarily queued in a distributed message queue (e.g., Apache Kafka) and processed asynchronously by the Voting Service. This ensures that the system can handle spikes in voting activity without overwhelming the database.

Algorithms and Data Structures

• Encryption:
• AES-256 encryption is used for securing vote data. Each vote is encrypted with a unique key derived from the election ID and voter ID, ensuring that even if one key is compromised, only that particular vote is at risk.
• Idempotency Key:
• A unique idempotency key is generated for each vote submission based on the voter ID, election ID, and a timestamp. This key is used to ensure that duplicate requests do not result in multiple votes being recorded.

Vote Storage & Tabulation Service

Overview

The Vote Storage & Tabulation Service is responsible for securely storing votes and efficiently tabulating the results. It plays a critical role in ensuring that the final election results are accurate, transparent, and available in real-time.

Internal Architecture

• Vote Storage Module:
• Manages the secure storage of encrypted votes. It interacts with the database to store votes in a way that maintains their confidentiality and integrity.
• Tabulation Engine:
• Aggregates the votes for each candidate within an election. This engine must handle large-scale data aggregation efficiently, ensuring that results are accurate and up-to-date.
• Cache Layer:
• Implements a caching mechanism (e.g., Redis) to store intermediate tabulation results. This allows the system to provide real-time updates to authorized users without re-computing results from scratch.
• Audit Trail Module:
• Records all tabulation activities to the Audit Logs, ensuring that the process is fully transparent and can be audited post-election.

Scalability Considerations

• Distributed Tabulation:
• For large elections, the tabulation process can be distributed across multiple nodes, each handling a portion of the total votes. This reduces the load on individual servers and speeds up the overall process.
• Incremental Updates:
• Instead of recalculating the entire tabulation each time a new vote is cast, the system updates the results incrementally. This reduces the computational load and improves the responsiveness of the results interface.
• Database Replication:
• The Vote table is replicated across multiple database instances to ensure high availability and fault tolerance. This also allows read-heavy operations like tabulation to be spread across different replicas.

Algorithms and Data Structures

• MapReduce for Distributed Tabulation:
• For national elections, a MapReduce approach is used to distribute the tabulation across multiple servers. Each server aggregates votes for a subset of candidates, and the results are then combined to produce the final tally.
• Merkle Trees for Auditability:
• Merkle Trees are used to create a verifiable chain of vote data. This data structure allows auditors to verify that the vote data has not been tampered with, without revealing the content of individual votes.

Design Considerations

Security:

• Both components emphasize end-to-end encryption, secure data storage, and robust authentication to protect against tampering and ensure voter privacy.

Performance:

• The use of caching, distributed processing, and incremental updates ensures that the system can handle large-scale elections efficiently, providing real-time results without sacrificing accuracy.

Auditability:

• Detailed audit logs and the use of verifiable data structures like Merkle Trees ensure that the voting process can be independently verified without compromising the secrecy of individual votes.

Trade offs/Tech choices

Centralized vs. Decentralized Architecture

• Decision: The system uses a centralized architecture with a distributed database layer and services.
• Trade-Off:
• Pros: Centralized architecture allows for easier management, monitoring, and enforcement of security policies. It also simplifies the implementation of complex business logic and auditability features.
• Cons: A decentralized architecture (e.g., using blockchain) could enhance transparency and reduce the risk of tampering by distributing trust across multiple nodes. However, blockchain systems often come with high costs in terms of performance and scalability, particularly for national-scale elections with millions of voters.
• Rationale: The decision to use a centralized system was driven by the need for high performance, scalability, and the ability to enforce strict security and audit requirements. The added complexity and potential performance issues of a decentralized system outweighed its benefits for this application.

2. Encryption Methodologies

• Decision: Use AES-256 encryption for securing votes and voter data.
• Trade-Off:
• Pros: AES-256 is widely recognized for its strength and efficiency, providing robust encryption while still being fast enough for real-time systems. It ensures that vote data remains confidential even in case of database breaches.
• Cons: Strong encryption increases computational overhead, especially when encrypting/decrypting large amounts of data. Additionally, key management becomes more complex.
• Rationale: The priority in the voting system is security, particularly the confidentiality and integrity of votes. The computational cost is justified by the critical need to protect vote data from tampering or unauthorized access.

3. Real-Time Tabulation vs. Batch Processing

• Decision: Use real-time tabulation with incremental updates.
• Trade-Off:
• Pros: Real-time tabulation provides instant feedback on election progress, allowing administrators to monitor the results as they come in. This improves transparency and can reduce the time required to announce final results.
• Cons: Real-time processing can be more resource-intensive and complex, especially under high load, compared to batch processing, which could be scheduled during off-peak hours.
• Rationale: The need for timely and accurate results outweighs the additional resource requirements. Elections, particularly large ones, are high-stakes events where delays in result reporting could lead to mistrust or unrest.

4. Caching vs. Direct Database Access for Tabulation

• Decision: Use a caching layer (e.g., Redis) for storing intermediate tabulation results.
• Trade-Off:
• Pros: Caching reduces the load on the database, especially during periods of high traffic when multiple users may be querying results. It also speeds up the retrieval of tabulation data, providing near-instant access to election results.
• Cons: Caches introduce complexity in ensuring that data is up-to-date and consistent with the database. If not managed correctly, stale or inconsistent data could lead to inaccurate tabulation results being presented.
• Rationale: The performance benefits of caching, particularly for read-heavy operations like vote tabulation, were deemed critical for ensuring a responsive system. By carefully managing cache invalidation and ensuring consistency, the risks of stale data can be mitigated.

Failure Scenarios/Bottlenecks

1. High Traffic Overload

Scenario:

• During peak voting periods, especially in national elections, the system may experience a sudden surge in traffic. If the system is not equipped to handle this load, it could result in slow response times or even system crashes.

Mitigation:

• Load Balancing: Implement dynamic load balancing across multiple servers to distribute traffic evenly.
• Auto-Scaling: Use cloud-based auto-scaling to add more server instances automatically when traffic exceeds a certain threshold.
• Rate Limiting: Apply rate limiting on the API Gateway to prevent any single user or a group of users from overwhelming the system.

2. Database Bottleneck

Scenario:

• The database may become a bottleneck, especially during the vote tabulation process, when many read and write operations occur simultaneously. This can lead to slow query performance or database unavailability.

Mitigation:

• Database Sharding: Distribute the database across multiple shards to spread the load. Sharding by election ID can ensure that no single shard is overwhelmed.
• Read Replicas: Use read replicas to offload read operations from the primary database. This is especially useful during vote tabulation when many users may be querying results.
• Caching: Implement a caching layer (e.g., Redis) for frequently accessed data, such as election results, to reduce the load on the database.

3. Data Corruption or Loss

Scenario:

• In the event of a system crash, power failure, or software bug, there is a risk of data corruption or loss. This could compromise the integrity of the election data, leading to incorrect results or loss of voter records.

Mitigation:

• Regular Backups: Implement automated backups at regular intervals. Store backups in multiple geographic locations to prevent data loss due to a regional disaster.
• Database Transactions: Use ACID-compliant transactions to ensure data consistency and integrity. This ensures that vote casting and other critical operations are either fully completed or not executed at all.
• Data Replication: Use real-time data replication across multiple database instances to ensure that data is always available and up-to-date.

4. Failure of Authentication Service

Scenario:

• If the Authentication Service fails, voters may be unable to log in and cast their votes, effectively preventing them from participating in the election.

Mitigation:

• Redundant Services: Deploy redundant instances of the Authentication Service across different availability zones to ensure it remains operational even if one instance fails.
• Graceful Degradation: Implement a fallback mechanism that allows voters to authenticate using alternative methods (e.g., email-based login links) if the primary service is unavailable.
• Service Health Monitoring: Continuously monitor the health of the Authentication Service. Use automated failover to switch to a backup instance if the primary instance fails.