AES 256 with PKCS7/PKCS5 padding GST E-Invoice

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I have to decrypt the encrypted SEK using APP key and encode JSON data using decrypted SEK to post for E-invoice Generation and sample code for Java and C# and I have converted in PHP but unfortunately failed to get desired output in PHP OpenSSL is not supported from my point as I am trying from last week

Sample JAVA & C# Code For Encryption and decryption

https://einv-apisandbox.nic.in/sample-code-in-java.html https://einv-apisandbox.nic.in/sample-code-in-c-sharp-dot-net.html

The goal is to decrypt and encrypt data using OpenSSL in PHP

my implementation as of now -

public function encrypt1($data, $secret_key)
  {
    return base64_encode(openssl_encrypt(base64_decode($data), $method='AES-256-ECB', base64_decode($secret_key), OPENSSL_RAW_DATA));
  }


  public function decrypt1($data,$secret_key)
  {
    return base64_encode(openssl_decrypt(base64_decode($data), $method='AES-256-ECB', $secret_key, OPENSSL_RAW_DATA));
  }
php-7 openssl encryption php
1 Answers

The decryption of the session key (SEK) with the AppKey is possible in PHP as follows:

function decryptBySymmetricKey($encSekB64, $appKey) {
    $sek = openssl_decrypt($encSekB64, "aes-256-ecb", $appKey, 0);                  // the SEK
    $sekB64 = base64_encode($sek);                                                  // the Base64 encoded SEK
    return $sekB64;
}

The encryption of data with the SEK is possible in PHP as follows:

function encryptBySymmetricKey($dataB64, $sekB64){
    $data = base64_decode($dataB64);                                                // the data to encrypt
    $sek = base64_decode($sekB64);                                                  // the SEK
    $encDataB64 = openssl_encrypt($data, "aes-256-ecb", $sek, 0);                   // the Base64 encoded ciphertext
    return $encDataB64;
}

Both functions can be tested with the following data:

$appKey = 'fao1PoKaLgd11xMrWTiL2cggAfx9QMwM';                                       // the 32 bytes AppKey
$encSekB64 = 'oRvKfBtmgNTSuk/oXUhiLOjXi45jiWA2oKNxhhQM3UH2o/32YWGLbUjK1/dohPe3';    // the Base64 encoded encrypted SEK 
$dataB64 = 'VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZw==';          // the base64 encoded data
$sekB64 = decryptBySymmetricKey($encSekB64, $appKey);                               // the Base64 encoded SEK   
$encDataB64 = encryptBySymmetricKey($dataB64, $sekB64);                             // the Base64 encoded ciphertext
echo $sekB64 . "\n";                                                                // zVoede7m2nnvMHcWYIfKhrvsilSFEZYiltJmxVQQnAQ=
echo $encDataB64;                                                                   // JS+hxYf64FMHThrhoIejqk3VjGwFw+GTYzUyVKc6GEOLKERVuvaNY91zPdo829r0

Comparison with C# reference code:

The linked C# methods DecryptBySymmetricKey and EncryptBySymmetricKey return with

byte[] appKey = Encoding.UTF8.GetBytes("fao1PoKaLgd11xMrWTiL2cggAfx9QMwM");
string encSekB64 = "oRvKfBtmgNTSuk/oXUhiLOjXi45jiWA2oKNxhhQM3UH2o/32YWGLbUjK1/dohPe3";
string dataB64 = "VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZw==";
string sekB64 = DecryptBySymmetricKey(encSekB64, appKey);
string encDataB64 = EncryptBySymmetricKey(dataB64, sekB64);
Console.WriteLine(sekB64);      // zVoede7m2nnvMHcWYIfKhrvsilSFEZYiltJmxVQQnAQ=
Console.WriteLine(encDataB64);  // JS+hxYf64FMHThrhoIejqk3VjGwFw+GTYzUyVKc6GEOLKERVuvaNY91zPdo829r0

the same values.

user_90140970
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