How to Properly Convert Byte Array to String and Back in Java for Encryption?

What is the correct way to convert a byte array to a string and back in Java for encryption without data loss?

public byte[] encrypt(String input) throws Exception {
    cipher.init(Cipher.ENCRYPT_MODE, key);
    byte[] inputBytes = input.getBytes("UTF-16");
    return cipher.doFinal(inputBytes);
}

public String decrypt(byte[] encryptionBytes) throws Exception {
    cipher.init(Cipher.DECRYPT_MODE, key);
    byte[] recoveredBytes = cipher.doFinal(encryptionBytes);
    return new String(recoveredBytes, "UTF-16");
}

Converting between byte arrays and strings in Java can present challenges, especially when dealing with encryption and decryption. Differences in encoding can lead to data loss, causing decryption processes to fail. This guide presents effective strategies for managing these conversions, ensuring consistency and correctness in your encryption workflow.

import java.util.Base64;

public byte[] encrypt(String input) throws Exception {
    cipher.init(Cipher.ENCRYPT_MODE, key);
    byte[] inputBytes = input.getBytes("UTF-8");
    return cipher.doFinal(inputBytes);
}

public String decrypt(byte[] encryptionBytes) throws Exception {
    cipher.init(Cipher.DECRYPT_MODE, key);
    byte[] recoveredBytes = cipher.doFinal(encryptionBytes);
    return new String(recoveredBytes, "UTF-8");
}

public String encodeToString(byte[] bytes) {
    return Base64.getEncoder().encodeToString(bytes);
}

public byte[] decodeFromString(String string) {
    return Base64.getDecoder().decode(string);
}

Causes

• The encoding used to convert strings to byte arrays can alter the data if not correctly matched during the reverse conversion.
• Using different character sets can lead to unexpected byte sequences, which will result in failed encryption and decryption processes.
• Java's string handling may introduce extra byte information, especially when working with strings that contain special characters.

Solutions

• Use Base64 encoding to convert byte arrays to strings, ensuring that no data is lost during conversion.
• Maintain consistent encoding (choose between UTF-8, UTF-16 etc.) throughout your encryption and decryption processes.
• Consider using Hex or Binary literals for representation when debugging or logging byte arrays.

Mistake: Inconsistent encoding during conversions (e.g., using 'UTF-16' to encode and 'UTF-8' to decode).

Solution: Always use the same encoding for both operations to ensure data integrity.

Mistake: Attempting to print the byte array directly, leading to unclear output.

Solution: Always convert the byte array to a Base64 string or hex for readable output.

Mistake: Not accounting for padding and formatting during encryption.

Solution: Ensure that the encryption/decryption methods appropriately handle padding as specified by the Cipher configuration.