Flutter中如何将现有AES/CBC/PKCS7Padding加解密代码转换为AES/CBC/PKCS5Padding实现？

Problem Description #

I currently have this AES encryption/decryption implementation in Flutter using the encrypt package, which uses AES/CBC/PKCS7Padding:

static String encKey = 'oasterw4567ncdsagfhswtoslfiessgv'; 
static final key = encrypt.Key.fromUtf8(encKey); 
static final iv = encrypt.IV.fromLength(16); 
static final encrypter = encrypt.Encrypter( 
  encrypt.AES(key, mode: encrypt.AESMode.cbc, padding: 'PKCS7')); 
static encryptAES(text) { 
  final encrypted = encrypter.encrypt(text, iv: iv); 
  print("Encrypted " + encrypted.base64); 
  decryptAES(encrypted.base64); 
  return encrypted.base64; 
} 
static decryptAES(encText) { 
  String original = encrypter.decrypt(encrypt.Encrypted.from64(encText), iv: iv); 
  print("Decrypt " + original); 
}

Now my client requires switching to AES/CBC/PKCS5Padding. How should I modify this code?

Answer #

Great question! Let's adjust your code and clarify some key points first:

First, a quick note on PKCS5 vs PKCS7 Padding: PKCS5Padding is technically a subset of PKCS7Padding (it only works with 8-byte block sizes), while AES uses a 16-byte block size. However, most modern encryption libraries (including the encrypt package you're using) handle PKCS5Padding correctly for AES by aligning it with the 16-byte block size.

To switch your implementation to AES/CBC/PKCS5Padding, you only need to make one small change to your code: update the padding parameter in the AES constructor from 'PKCS7' to 'PKCS5'.

Here's the modified full code:

static String encKey = 'oasterw4567ncdsagfhswtoslfiessgv'; 
static final key = encrypt.Key.fromUtf8(encKey); 
static final iv = encrypt.IV.fromLength(16); 
static final encrypter = encrypt.Encrypter( 
  // Changed padding from 'PKCS7' to 'PKCS5'
  encrypt.AES(key, mode: encrypt.AESMode.cbc, padding: 'PKCS5')); 
static encryptAES(text) { 
  final encrypted = encrypter.encrypt(text, iv: iv); 
  print("Encrypted " + encrypted.base64); 
  decryptAES(encrypted.base64); 
  return encrypted.base64; 
} 
static decryptAES(encText) { 
  String original = encrypter.decrypt(encrypt.Encrypted.from64(encText), iv: iv); 
  print("Decrypt " + original); 
}

Key Notes to Keep in Mind: #

• Key Length: Your current key is 32 bytes (256 bits), which is valid for AES-256. This doesn't need to change for PKCS5Padding.
• IV Requirement: CBC mode requires the IV to be the same size as the AES block size (16 bytes). Your IV.fromLength(16) is correct and should stay as-is.
• Cross-System Validation: If you're communicating with another system that uses PKCS5Padding, make sure to test end-to-end encryption/decryption to confirm compatibility (e.g., encrypt in Flutter, decrypt in the target system and vice versa).

内容的提问来源于stack exchange，提问作者amit.flutter