Hey there! Let's break down exactly what you need to do to get your AES/CBC/PKCS7Padding encryption matching the target example. The key here is that every single parameter has to align perfectly—even a tiny mismatch will throw off your result. Here's a step-by-step breakdown of the critical details you need to nail down:

• Key Size & Value: AES supports 128, 192, or 256-bit keys. You must use the exact same key as the example—check if it's provided as a raw byte array, hex string, or base64-encoded string, and decode it correctly. For example, if the example uses a 256-bit key given as a hex string, don't treat it as a UTF-8 string; convert the hex directly to bytes.
• Initialization Vector (IV): CBC mode requires an IV, and it has to be exactly 16 bytes (the block size for AES) and match the example's IV exactly. Important: The IV doesn't need to be secret, but it must be identical for both encryption and decryption to get matching results. Don't generate a random IV here—use the exact one from the example.
• Input Data Encoding: Make sure your plaintext uses the same character encoding as the example. Is it UTF-8? ASCII? A raw byte array? If the example encrypts "hello world" as UTF-8, using ISO-8859-1 encoding for your input will produce a different ciphertext.
• Output Format: How is the example's encrypted result formatted? Is it a hex string, base64 string, or raw bytes? You need to encode your encrypted bytes the same way to match. For example, if the example shows a base64 string, take your ciphertext bytes and encode them to base64, not hex.
• Padding Scheme: Double-check that you're using PKCS7Padding specifically. While PKCS5Padding is often interchangeable for 8-byte block sizes like AES, it's safer to use the exact padding scheme specified to avoid unexpected differences.

Let's say your example uses these concrete values:

• Key: my256bitkey1234567890abcdef (256-bit, UTF-8 encoded)
• IV: 1234567890abcdef (16 bytes, UTF-8 encoded)
• Plaintext: test data (UTF-8)
• Output: Base64 encoded ciphertext

Here's how you'd implement it to match the example:

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.util.Base64;

public class AESExample {
    public static void main(String[] args) throws Exception {
        // Exact parameters pulled from the example
        String plaintext = "test data";
        String keyStr = "my256bitkey1234567890abcdef";
        String ivStr = "1234567890abcdef";
        
        // Convert key and IV to bytes using the same encoding as the example
        byte[] keyBytes = keyStr.getBytes("UTF-8");
        byte[] ivBytes = ivStr.getBytes("UTF-8");
        
        // Initialize cipher with the exact algorithm specification
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
        SecretKeySpec keySpec = new SecretKeySpec(keyBytes, "AES");
        IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
        cipher.init(Cipher.ENCRYPT_MODE, keySpec, ivSpec);
        
        // Encrypt and encode the result to match the example's output format
        byte[] ciphertextBytes = cipher.doFinal(plaintext.getBytes("UTF-8"));
        String ciphertextBase64 = Base64.getEncoder().encodeToString(ciphertextBytes);
        
        System.out.println("Encrypted result: " + ciphertextBase64);
    }
}

• Key/IV Encoding Mismatch: If the example uses a hex-encoded key, don't decode it as UTF-8—use a hex-to-byte utility (like Hex.decodeHex(keyStr.toCharArray()) from Apache Commons Codec) instead.
• IV Length Issues: AES's IV must be 16 bytes. If your example's IV is shorter or longer, you might be missing a step (like hashing the IV to get 16 bytes, but this is rare—usually the example will provide a 16-byte IV).
• Cipher String Variations: Some libraries use slightly different cipher strings, like AES/CBC/PKCS5Padding (equivalent for AES but not identical in spec) or requiring a provider (e.g., AES/CBC/PKCS7Padding/BC for BouncyCastle). Make sure your cipher string matches what the example uses.

内容的提问来源于stack exchange，提问作者user1318741