This README provides an in-depth exploration of data security and cryptography in the fintech sector. We'll cover encryption techniques, secure key management, compliance with security standards, and provide Java examples for practical implementations.

• Advanced Encryption Standard (AES) is used for encrypting transaction data and personal information. It is preferred for its speed and security, making it ideal for securing large volumes of data.

• RSA (Rivest–Shamir–Adleman) is utilized for secure data transmission over untrusted networks and for digital signatures. It uses a pair of keys (public and private) to ensure that data can be encrypted by anyone with the public key but decrypted only by the holder of the private key.

Here's a simple scenario where a fintech application needs to securely transmit credit card information:

1. Data Encryption: The client application uses the server's public key to encrypt the credit card information.
2. Data Transmission: The encrypted data is sent over the internet to the server.
3. Data Decryption: The server uses its private key to decrypt the information upon receipt.

Efficient key management is crucial for maintaining the security of cryptographic keys. This includes:

• Hardware Security Modules (HSMs): Used to manage and safeguard encryption keys. HSMs provide a physically secure environment for cryptographic operations.
• Key Rotation Policies: Regular changing of keys to minimize the risk of compromise. Data is re-encrypted with new keys as part of this policy.

• AES: Recommended with a key size of 256 bits as per PCI DSS standards for payment data protection.
• RSA: Keys should be at least 2048 bits long to safeguard against modern computational threats.

Below is a Java example demonstrating the use of RSA for key wrapping and AES for data encryption:

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PublicKey;

public class EncryptionExample {
    public static void main(String[] args) throws Exception {
        // Generate RSA keys
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        KeyPair keyPair = keyPairGenerator.generateKeyPair();

        // Generate AES key
        KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
        keyGenerator.init(256);
        SecretKey aesKey = keyGenerator.generateKey();

        // Encrypt AES key with RSA public key
        Cipher rsaCipher = Cipher.getInstance("RSA");
        rsaCipher.init(Cipher.WRAP_MODE, keyPair.getPublic());
        byte[] wrappedAesKey = rsaCipher.wrap(aesKey);

        // Assume this wrapped key would be securely transmitted to the server
        // Server would use private key to unwrap the AES key
        rsaCipher.init(Cipher.UNWRAP_MODE, keyPair.getPrivate());
        SecretKey unwrappedAesKey = (SecretKey) rsaCipher.unwrap(wrappedAesKey, "AES", Cipher.SECRET_KEY);

        // Use AES key for data encryption/decryption
        Cipher aesCipher = Cipher.getInstance("AES");
        aesCipher.init(Cipher.ENCRYPT_MODE, unwrappedAesKey);
        // Encryption and decryption of data can now be performed using aesCipher
    }
}

In this example, RSA is used to securely transmit an AES key, which is then used for encrypting data. This showcases a practical application of combining asymmetric and symmetric encryption to achieve security in data transmission.