create composer installer

composer.json

@@ -0,0 +1,25 @@
+{
+    "name": "paytm/paytmchecksum",
+    "description": "This is for paytm checksum creation and verification in PHP",
+    "keywords": [  "Paytm", "Checksum", "Paytm PHP", "Paytm checksum", "Paytm signature", "Signature", "Paytm payment"],
+    "type": "library",
+    "authors": [
+    {
+      "name": "Soumya Vats",
+      "role": "Developer"
+    }
+   ],
+     "homepage": "https://developer.paytm.com/docs/checksum/#php",
+    "require": {
+        "ext-json": "*",
+        "php": ">=5.6.0",
+        "ext-curl": "*",
+        "ext-openssl": "*",
+        "netresearch/jsonmapper": "^1.4",
+        "monolog/monolog": "^1.24"
+    },
+ "autoload": {
+        "psr-4": {"paytm\\paytmchecksum\\": "paytmchecksum/"}
+    },
+    "license": "MIT"
+}

paytmchecksum/PaytmChecksum.php

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+<?php
+/**
+ * Paytm uses checksum signature to ensure that API requests and responses shared between your 
+ * application and Paytm over network have not been tampered with. We use SHA256 hashing and 
+ * AES128 encryption algorithm to ensure the safety of transaction data.
+ *
+ * @author     Lalit Kumar
+ * @version    2.0
+ * @link       https://developer.paytm.com/docs/checksum/#php
+ */
+
+namespace paytm\paytmchecksum;
+
+class PaytmChecksum{
+
+	private static $iv = "@@@@&&&&####$$$$";
+
+	static public function encrypt($input, $key) {
+		$key = html_entity_decode($key);
+
+		if(function_exists('openssl_encrypt')){
+			$data = openssl_encrypt ( $input , "AES-128-CBC" , $key, 0, self::$iv );
+		} else {
+			$size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, 'cbc');
+			$input = self::pkcs5Pad($input, $size);
+			$td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', 'cbc', '');
+			mcrypt_generic_init($td, $key, self::$iv);
+			$data = mcrypt_generic($td, $input);
+			mcrypt_generic_deinit($td);
+			mcrypt_module_close($td);
+			$data = base64_encode($data);
+		}
+		return $data;
+	}
+
+	static public function decrypt($encrypted, $key) {
+		$key = html_entity_decode($key);
+
+		if(function_exists('openssl_decrypt')){
+			$data = openssl_decrypt ( $encrypted , "AES-128-CBC" , $key, 0, self::$iv );
+		} else {
+			$encrypted = base64_decode($encrypted);
+			$td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', 'cbc', '');
+			mcrypt_generic_init($td, $key, self::$iv);
+			$data = mdecrypt_generic($td, $encrypted);
+			mcrypt_generic_deinit($td);
+			mcrypt_module_close($td);
+			$data = self::pkcs5Unpad($data);
+			$data = rtrim($data);
+		}
+		return $data;
+	}
+
+	static public function generateSignature($params, $key) {
+		if(!is_array($params) && !is_string($params)){
+			throw new Exception("string or array expected, ".gettype($params)." given");			
+		}
+		if(is_array($params)){
+			$params = self::getStringByParams($params);			
+		}
+		return self::generateSignatureByString($params, $key);
+	}
+
+	static public function verifySignature($params, $key, $checksum){
+		if(!is_array($params) && !is_string($params)){
+			throw new Exception("string or array expected, ".gettype($params)." given");
+		}
+		if(isset($params['CHECKSUMHASH'])){
+			unset($params['CHECKSUMHASH']);
+		}
+		if(is_array($params)){
+			$params = self::getStringByParams($params);
+		}		
+		return self::verifySignatureByString($params, $key, $checksum);
+	}
+
+	static private function generateSignatureByString($params, $key){
+		$salt = self::generateRandomString(4);
+		return self::calculateChecksum($params, $key, $salt);
+	}
+
+	static private function verifySignatureByString($params, $key, $checksum){
+		$paytm_hash = self::decrypt($checksum, $key);
+		$salt = substr($paytm_hash, -4);
+		return $paytm_hash == self::calculateHash($params, $salt) ? true : false;
+	}
+
+	static private function generateRandomString($length) {
+		$random = "";
+		srand((double) microtime() * 1000000);
+
+		$data = "9876543210ZYXWVUTSRQPONMLKJIHGFEDCBAabcdefghijklmnopqrstuvwxyz!@#$&_";	
+
+		for ($i = 0; $i < $length; $i++) {
+			$random .= substr($data, (rand() % (strlen($data))), 1);
+		}
+
+		return $random;
+	}
+
+	static private function getStringByParams($params) {
+		ksort($params);		
+		$params = array_map(function ($value){
+			return ($value !== null && strtolower($value) !== "null") ? $value : "";
+	  	}, $params);
+		return implode("|", $params);
+	}
+
+	static private function calculateHash($params, $salt){
+		$finalString = $params . "|" . $salt;
+		$hash = hash("sha256", $finalString);
+		return $hash . $salt;
+	}
+
+	static private function calculateChecksum($params, $key, $salt){
+		$hashString = self::calculateHash($params, $salt);
+		return self::encrypt($hashString, $key);
+	}
+
+	static private function pkcs5Pad($text, $blocksize) {
+		$pad = $blocksize - (strlen($text) % $blocksize);
+		return $text . str_repeat(chr($pad), $pad);
+	}
+
+	static private function pkcs5Unpad($text) {
+		$pad = ord($text{strlen($text) - 1});
+		if ($pad > strlen($text))
+			return false;
+		return substr($text, 0, -1 * $pad);
+	}
+}