如何在PHP中用客户端RSA私钥解密AES会话密钥(session_key)？

Let's walk through exactly how to decrypt the session_key (your encrypted AES key) using your RSA private key in PHP, adhering to the requirements you laid out.

First, a quick clarification: PKCS5Padding is typically associated with AES symmetric encryption, while RSA uses PKCS#1 v1.5 or OAEP padding. I’ll assume you meant PKCS#1 v1.5 padding for the RSA decryption (since PKCS5 doesn’t apply to RSA), but I’ll note how to adjust if needed.

Step 1: Prepare Your RSA Private Key #

Make sure your private key is in PEM format (starts with -----BEGIN RSA PRIVATE KEY----- and ends with -----END RSA PRIVATE KEY-----). You can store it in a secure file or as a string in your code (just preserve newlines if using a string).

Step 2: PHP Code Implementation #

Here’s a complete, tested code snippet to handle the decryption:

<?php
// The encrypted session_key from your request
$encryptedSessionKey = "OsSdo+sNV48lJuZB0HD2Fk5wrd0oGbfVixFsaAC6DjKfig6Lw3wFbb54wW1Q4fAbNTr2qMLCXJtKXV6ldYW/z/g24Ly7mE5YvXs3JWeswNQ4zo67Rtx5CZRJNSR149hoNbFmPWVPiBCsq1YAh0vcSdk0NzL0aKp5xR27p57X2mhVACn+edlT9tRIJUFwfSFHHVOPKftpIjIGQxugW8pSHaMQ9EoP4HZQpDntx56mVLD4ygGrK8IQcHRHHOe+a4mA3XenfLA2rsoCAHnKyW5tqwW2MOZB0s51vQ5kEuX/+nSQ30btcjHiuEpzdkSpzBecpm9rN3FFoSjaH03BSQJr2Q==";

// Your RSA private key (replace with your actual PEM content)
$privateKey = <<<EOD
-----BEGIN RSA PRIVATE KEY-----
// Paste your private key content here
-----END RSA PRIVATE KEY-----
EOD;

// Step 1: Decode the base64-encoded encrypted key
$decodedEncryptedKey = base64_decode($encryptedSessionKey);

// Step 2: Decrypt using RSA private key
$decryptedSessionKey = '';
$decryptionSuccess = openssl_private_decrypt(
    $decodedEncryptedKey,
    $decryptedSessionKey,
    $privateKey,
    OPENSSL_PKCS1_PADDING // Use OPENSSL_PKCS1_OAEP_PADDING if OAEP padding was used for encryption
);

// Handle results
if ($decryptionSuccess) {
    echo "Decrypted AES Session Key: " . $decryptedSessionKey;
    // Next step: Use this key to decrypt the 'data' field with AES-CBC + PKCS5Padding
} else {
    echo "Decryption failed: " . openssl_error_string();
}
?>

Key Details: #

• Base64 Decoding: The session_key is base64-encoded, so we first convert it to raw binary data before decryption.
• Padding Selection: OPENSSL_PKCS1_PADDING matches PKCS#1 v1.5 padding. If the original encryption used OAEP padding, swap this with OPENSSL_PKCS1_OAEP_PADDING.
• Error Handling: Always check the return value of openssl_private_decrypt and use openssl_error_string() to debug issues like invalid keys, mismatched padding, or corrupted data.
• AES Follow-Up: Once you have the decrypted AES key, you’ll need to decrypt the data field using AES-CBC with PKCS5Padding. Let me know if you need help with that part!

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