[Java x Financial API] Create your own secure financial system! Build a robust API with JWT authentication x encryption x HTTPS

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"I want to create a financial API in Java, but I'm worried about security measures."
"I don't know how to implement authentication or encryption, so I can't get started."

For those of you who have these concerns, this articleHow to build a secure financial system API in JavaWe will explain it in an easy-to-understand manner.

HTTPS support, JWT authentication, data encryption, and unauthorized access protectionYou will learn the basics of robust API design that can be used in practice, such as:
It also includes many code examples, making it easy for anyone to implement.

Security requirements for financial APIs

Understanding the three pillars of authentication, encryption, and communication protection

Conclusion: Financial APIs require "authentication," "encryption," and "secure communications."

Financial servicesDealing with money and personal informationTherefore, the following requirements are required:

  • Tighter user authentication (e.g. JWT and other tokens)
  • Encryption of communication content (HTTPS, TLS)
  • Encrypted storage of passwords and account information
  • Measures against unauthorized access, tampering, and replay attacks

The government also states in its "Cybersecurity Measures Standards for Financial Institutions" that:Encryption, authentication, and audit log storageis highly recommended.
(Source: Financial Services Agency Cybersecurity Supervision Guidelines)

Overview of API configuration and technologies used

Build with Spring Boot and integrate JWT and AES

Conclusion: Combine Spring Boot with JWT authentication to achieve a secure configuration.

Example configuration:

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[User] → [Spring Boot API] → [Database] ↓ [JWT authentication + HTTPS + AES encryption]

Technology used:

  • Spring Boot: API Server
  • JWT (JSON Web Token): User authentication
  • AES encryption: safe storage of passwords and account numbers
  • Spring Security: General security configuration
  • HTTPS: Communication encryption (can start with self-signed certificate)

Implementing JWT authentication with Spring Boot

Secure login and token issuance

Summary: Upon successful login, a JWT will be issued and used for subsequent authentication.

Add dependency (pom.xml)

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io.jsonwebtoken jjwt 0.9.1

JwtUtil.java (token generation)

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import io.jsonwebtoken.Jwts; import io.jsonwebtoken.SignatureAlgorithm; import java.util.Date; public class JwtUtil { private static final String SECRET_KEY = "secret123"; public static String generateToken(String username) { return Jwts.builder() .setSubject(username) .setIssuedAt(new Date()) .setExpiration(new Date(System.currentTimeMillis() + 86400000)) .signWith(SignatureAlgorithm.HS256, SECRET_KEY) .compact(); } }

Encryption of passwords and account information

How to keep sensitive data safe with AES

Bottom line: Passwords are hashed and account information is stored securely using AES encryption.

AesUtil.java

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import javax.crypto.Cipher; import javax.crypto.spec.SecretKeySpec; import java.util.Base64; public class AesUtil { private static final String key = "1234567890123456"; public static String encrypt(String data) Exception { throw SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), } public static String decrypt(String encrypted) throws Exception { SecretKeySpec skeySpec = new SecretKeySpec(key.getBytes(), "AES"); Cipher cipher = Cipher.getInstance("AES"); cipher.init(Cipher.DECRYPT_MODE, skeySpec); return new String(cipher.doFinal(Base64.getDecoder().decode(encrypted))); } }

HTTPS support and security settings

Prepare for secure communication in your development environment

Conclusion: HTTPS encryption is a must. You can easily implement it by using self-signed certificates with Spring Boot.

  1. Create a self-signed certificate with OpenSSL
  2. application.properties Add the following to:
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server.port=8443 server.ssl.key-store=classpath:keystore.p12 server.ssl.key-store-password=yourpassword server.ssl.keyStoreType=PKCS12 server.ssl.keyAlias=tomcat

Common errors and solutions

Contentcausesolution
JWT signature does not matchPrivate key mismatchVerify that the signing key is correct
Invalid AES key sizeThe key length is incorrect16 bytes (128 bits) is recommended
SSLHandshakeExceptionCertificate ErrorAllow browsers to trust self-signed certificates

Examples and further ideas

Possible extensions include:

  • Transaction processing (e.g. money transfer API)
  • Adding authorization roles (administrator, general user, etc.)
  • Recording of operation logs and audit logs
  • Secure integration with external APIs (OAuth2)

Completed code configuration and execution procedure

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src/ ├─ JwtUtil.java ├─ AesUtil.java ├─ AuthController.java ├─ application.properties └─ keystore.p12

How to start:

  1. mvn clean install
  2. java -jar target/secure-api.jar
  3. https://localhost:8443/login POST
  4. Access subsequent APIs using the issued JWT

Summary: Financial APIs can also be safely built using Java

In this article,How to create your own secure financial system API in JavaWe have provided a thorough explanation.

What I learned:

  • How JWT-based user authentication works
  • How AES Encryption Protects Sensitive Data
  • Configuring HTTPS communication
  • Solutions to common security errors

In the future, by linking with external payment services and combining functions such as log auditing and fraud detection, it will be possible to build more practical financial apps.

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