PHP decryption fails on some lines with trim ()

Question

I'm having trouble decrypting values ​​that end in% 3D% 3D. After decryption, I get a return value that is completely inaudible. The encrypted value is passed through the request, but I checked the loop cycle with values ​​from 0 to 200 to eliminate problems with url encoding.

Encryption and Decryption Functions:

function encryptValue($encrypt) { $key = variable_get_local("privateKey", $default = ""); $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND); $passcrypt = trim(mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, trim($encrypt), MCRYPT_MODE_ECB, $iv)); $encode = urlencode(base64_encode($passcrypt)); return $encode; } function decryptValue($decrypt) { $key = variable_get_local("privateKey", $default = ""); $decoded = base64_decode(urldecode($decrypt)); $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND); $decrypted = trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, trim($decoded), MCRYPT_MODE_ECB, $iv)); return $decrypted; } 

I tried to keep the iv value the same for encryption and decryption, but this does not change the result. I also tried removing trim() around trim($decoded) , but didn't change anything.

Below I found out about the problem. Between 0 and 200, encryption will display a value that ends in% 3D% 3D 9 times and causes decryption to fail.

 for($i=0;$i<200;$i++) { echo encryptValue($i) . "<br/>"; echo decryptValue(encryptValue($i)) . "<br/><hr/>"; } 

Thank you for reading.

Answer 1

Your problem is with all trim functions that should not be used. You do not trim the encoded data, since the data will be deleted, it can be vital for the key, as you noticed.

It works as follows:

 function encryptValue($encrypt) { $key = variable_get_local("privateKey", $default = ""); $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND); $passcrypt = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $key, trim($encrypt), MCRYPT_MODE_ECB, $iv); $encode = urlencode(base64_encode($passcrypt)); return $encode; } function decryptValue($decrypt) { $key = variable_get_local("privateKey", $default = ""); $decoded = base64_decode(urldecode($decrypt)); $iv = mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND); $decrypted = mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $key, $decoded, MCRYPT_MODE_ECB, $iv); return $decrypted; } 

Answer 2

Here are some observations in the current script:

• ECB mode is not safe using CBC instead
• MCRYPT_RAND is the same as rand see str_shuffle and randomness use MCRYPT_DEV_URANDOM instead
• For increased security, use HMAC encryption + authentication to prevent the prevention of an Oracle attack. A.
• Also use a trusted library, not Zend\Crypt , and do not create your own sine. You are not a security expert.

Example:

 // Encription Key $encryptionKey = mcrypt_create_iv(16, MCRYPT_DEV_URANDOM); // Stored securely // Signature Key $signatureKey = mcrypt_create_iv(16, MCRYPT_DEV_URANDOM); // Stored securely // Start DataEncryption Object $obj = new DataEncryption($encryptionKey, $signatureKey); $obj->setEncoding(DataEncryption::ENCODE_BASE64); // Test for($i = 0; $i < 200; $i ++) { printf("%s = %s\n", $encode = $obj->encrypt($i), $obj->decrypt($encode)); } 

Output

 eSCknmsoMHY2oo5lpW3NpQhDigs4+Fw8aObeIhK+wPyUImQbvlh/aUrW = 0 qFswb3VO5+Foi4kjVn6s5lpZbiWgdKmfObh37/xjPyqB4ZFfAXNUeYYX = 1 WKG0BCKUxOXWU6S3YJ/dNL46Lcn7lt+ihG4tEoZuORDoJXSjz6Vrcepn = 2 K24QqkGYC86btzGQ5HKKMewVhiEIdKOajpgLx8SMKVKfCwlOJlbRwpaz = 3 0DbJycPZ24FOAhQrhQJmgMsP0p2nFzYUlFVOFlbQ8zhLTXkcdnNOhVfi = 4 l7saQG2BTPAZR2EnYjxfNmTxEBBaAh+n9+8eOCITDGzEVShw9wOxP7Pt = 5 eUhvvHJOFsy6ZaBu40XgU+N5VtuFBesRVx0ryfManIXva5y7J0ShiKcE = 6 TaX+172N60X1UTVmMWYcdcn7YzN7xoAOVEPpaD7r1pE3OtX5Erg4nja8 = 7 0LM3W0pkQ73IsmqAgRiQvqL0/rdkk7YvuwcVwoe1NI+qZo7Jq8gyFIvn = 8 .... 38m8fEoUhoTyPPBukg3KVhrmwVDyVCcnWx/5erAslUDzEP7Bddzj5y8Y = 196 Dwi6t7sX30bxjbVXMKCWEZs0FxTUZM4IPHKR3VD6kygi7op0Q6ARCZJW = 197 TJ/faDaIuE0mDPHmGar1BeIyAnfVD0Z47ZtCcHjz5AZzaQ1YWH8kF1bU = 198 FYh+8Kts4ubVvTT5o0vZYfKC+8ExhpD5pWgHK3EhvGWkcPwKerSIvkK0 = 199 

Used class

 class DataEncryption { private $keyEncryption; private $keySignature; private $ivSize; private $cipher = MCRYPT_RIJNDAEL_128; private $mode = MCRYPT_MODE_CBC; private $signatureLength = 10; private $encoding = 2; // I prefer hex const ENCODE_BASE64 = 1; const ENCODE_HEX = 2; function __construct($encryptionKey = null, $signatureKey = null) { // Set Keys $this->keyEncryption = empty($encryptionKey) ? mcrypt_create_iv(32, MCRYPT_DEV_URANDOM) : $encryptionKey; $this->keySignature = empty($signatureKey) ? mcrypt_create_iv(32, MCRYPT_DEV_URANDOM) : $signatureKey; // Get IV Size $this->ivSize = mcrypt_get_iv_size($this->cipher, $this->mode); } public function getKeys() { return array( "encryption" => $this->keyEncryption, "signature" => $this->keySignature ); } public function setMode($mode) { $this->mode = $mode; } public function setCipher($cipher) { $this->cipher = $cipher; } public function setEncoding($encode) { $this->encoding = $encode; } public function encrypt($data) { // add PKCS7 padding to data $block = mcrypt_get_block_size($this->cipher, $this->mode); $pad = $block - (strlen($data) % $block); $data .= str_repeat(chr($pad), $pad); $iv = $this->rand($this->ivSize); $cipherData = mcrypt_encrypt($this->cipher, $this->keyEncryption, $data, $this->mode, $iv); $finalData = $iv . $cipherData; // protected against padding oracle attacks $finalData = $this->sign($finalData) . $finalData; return $this->encode($finalData); } public function decrypt($data) { $data = $this->decode($data); // Check Integrity if (! $this->check($data)) { return false; } $data = substr($data, $this->signatureLength); // Break Data $iv = substr($data, 0, $this->ivSize); $cipherData = substr($data, $this->ivSize); $data = mcrypt_decrypt($this->cipher, $this->keyEncryption, $cipherData, $this->mode, $iv); // Remove PKCS7 padding $block = mcrypt_get_block_size($this->cipher, $this->mode); $pad = ord($data[($len = strlen($data)) - 1]); // $data = rtrim($data, "\0..\32"); return substr($data, 0, $len - $pad); } public function encode($data) { return $this->encoding === self::ENCODE_BASE64 ? base64_encode($data) : bin2hex($data); } public function decode($data) { return $this->encoding === self::ENCODE_BASE64 ? base64_decode($data) : pack("H*", $data); } public function sign($data) { $hash = hash_hmac('sha256', $data, $this->keySignature, true); return substr($hash, 0, $this->signatureLength); } public function check($data) { $signature = substr($data, 0, $this->signatureLength); $data = substr($data, $this->signatureLength); $hash = hash_hmac('sha256', $data, $this->keySignature, true); // return $signature === substr($hash, 0, $this->signatureLength); return $this->compare($signature, substr($hash, 0, $this->signatureLength)); } public function rand($no) { return mcrypt_create_iv($no, MCRYPT_DEV_URANDOM); } /** * Prevent Timing Attacks * @param string $a * @param string $b * @return boolean */ public function compare($a, $b) { if (strlen($a) !== strlen($b)) { return false; } $result = 0; for($i = 0; $i < strlen($a); $i ++) { $result |= ord($a[$i]) ^ ord($b[$i]); } return $result == 0; } }