How to solve php aes cbc decryption garbled code

In PHP, it is very common to use AES CBC mode for encryption and decryption. However, when using AES CBC mode to decrypt, you may encounter garbled characters. This problem is very common, but easy to solve. In this article, I will introduce how to normally decrypt AES CBC encrypted data through PHP and avoid garbled characters.

1. Problem description

In PHP, we can use openssl_encrypt and openssl_decrypt functions to perform encryption and decryption operations respectively. For example, the following code uses AES CBC mode to encrypt data:

$key = '1234567890123456';
$data = 'hello world';
$iv = '1234567890123456';

$encrypted = openssl_encrypt($data, 'AES-128-CBC', $key, OPENSSL_RAW_DATA, $iv);

where $key is the key, $data is the data to be encrypted, and $iv is the initial vector. After encryption, the $encrypted variable will get the encrypted data. Now, we need to decrypt it:

$key = '1234567890123456';
$encrypted = 'soLPpFUpwJdVEaYpuu6zRg==';
$iv = '1234567890123456';

$decrypted = openssl_decrypt($encrypted, 'AES-128-CBC', $key, OPENSSL_RAW_DATA, $iv);
echo $decrypted;

However, after running the above code, you may get the following output:

纭洏鍥?J    鍗虫槑涓?

This is a piece of gibberish, not the original data "hello world ". This is because the decryption function has strict limits on the length of the input parameters, so if the length of the data to be decrypted is incorrect, garbled characters will occur.

2. Solution

In order to solve this problem, we need to understand some basic knowledge of AES CBC mode.

In AES CBC mode, both encryption and decryption require an initialization vector (Initialization Vector, IV). This initial vector needs to use the same value during encryption and decryption, otherwise it will cause data errors during decryption.

The length of the initialization vector must be equal to the block size required by the encryption algorithm. For example, when using 128-bit AES CBC mode, the initialization vector must be 16 bytes long (128 bits / 8 bits). If this requirement is not met, garbled characters or other problems will occur during decryption.

Therefore, we need to check whether the length of the input parameter meets the requirements. When the length is illegal, padding operation is required. Padding can be done before decryption to ensure that the length of the input data is the same as that used when encrypting.

In view of the above problems and solutions, we can modify the original code to adapt to the requirements of AES CBC mode, as shown below:

$key = '1234567890123456';
$encrypted = 'soLPpFUpwJdVEaYpuu6zRg==';
$iv = '1234567890123456';

// 检查初始向量长度是否正确
if (strlen($iv) != 16) {
    echo 'Error: IV length is not valid!';
    exit;
}

// 检查输入参数长度是否正确
$decrypted = openssl_decrypt($encrypted, 'AES-128-CBC', $key, OPENSSL_RAW_DATA, $iv);
if ($decrypted === false) {
    // 进行填充操作
    $padded_data = $encrypted . str_repeat(chr(16), 16 - (strlen($encrypted) % 16));
    $decrypted = openssl_decrypt($padded_data, 'AES-128-CBC', $key, OPENSSL_RAW_DATA, $iv);
}

echo $decrypted;

In the above code, first check whether the initial vector length is correct. If it is incorrect, an error is output and the program exits. Next, the input data length before decryption is checked. If the length is incorrect, padding is performed to ensure that the data length meets the requirements.

In this way, garbled characters can be avoided during decryption.

3. Summary

When using AES CBC mode for encryption and decryption, if the length of the input parameter is incorrect, decryption may fail and garbled characters may appear. To avoid this problem, we need to check the length of the input parameters and perform necessary padding.

The above is my solution to the problem of decrypting garbled characters in PHP AES CBC mode. Hope it helps.

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