RSA Decryption with phpseclib is failing

Question

I have mobile application that encrypts strings with RSA and sends that encrypted data to PHP web server.

After a search I found that phpseclib is used to decrypt RSA Latest version 2.0.

No matter what I do I receive despite error despite used mode

Am i doing something wrong?

What I have tried:

Private key for decryption:

Encrypted message (base64 encoded):

SMZiVTAMizngWa5Yg2Xp0F3Coy4cIsLB6mru2rLhxnvS2SC\/rm9pgPVLdA\/hp+1TIbzHZqjc2lnP\nkvzh797WlA==\n

PHP sample code:

$rsa = new RSA();
$rsa->setEncryptionMode(RSA::ENCRYPTION_PKCS1);
$rsa->loadKey($privateKey); 
echo $rsa->decrypt(base64_decode($strBase64));

Result:

Notice: Decryption error in C:\xampp\htdocs\webservice\vendor\phpseclib\phpseclib\phpseclib\Crypt\RSA.php on line 2553

Mode:

$rsa->setEncryptionMode(RSA::ENCRYPTION_OAEP);

Result:

Notice: Decryption error in C:\xampp\htdocs\webservice\vendor\phpseclib\phpseclib\phpseclib\Crypt\RSA.php on line 2432

Mode:

$rsa->setEncryptionMode(RSA::ENCRYPTION_NONE);

Result:

string(128) "I�W��B'q����;k��}�1������=��x���*���_��aq�)�D� '�m{��� ��n���C:��t �E����R=�S�y�3$QC�EV.3C�{�.Y�jx�6��!�e�˱]�I ����S�/�'I�|"

I can't test php right now but the private in your question does decrypt the cipher in your question. NO padding is used. The result is a readable ASCII string. — President James K. Polk
– President James K. Polk, Commented Nov 30, 2018 at 14:45
@JamesKPolk - idk how you're doing your decryption but I'm not able to decrypt the OP's ciphertext. I did openssl rsautl -decrypt -in encrypted.txt -out plaintext.txt -raw -inkey priv.pem via the CLI and got a "data greater than mod len" back. This makes sense because the ciphertext is 65 bytes long whereas the modulo for the key is 64 bytes long (512 bits) — neubert
– neubert, Commented Dec 1, 2018 at 18:34
@neubert: I see now that the base64 encrypted message contains several invalid escape "\" characters and an embedded newline. Here is the value after removal of those characters: SMZiVTAMizngWa5Yg2Xp0F3Coy4cIsLB6mru2rLhxnvS2SC/rm9pgPVLdA/hp+1TIbzHZqjc2lnPkvzh797WlA== — President James K. Polk
– President James K. Polk, Commented Dec 1, 2018 at 19:28

neubert · Accepted Answer · 2018-12-01 20:52:45Z

2

As James J Polk observed, your base64 encoded string has some bad characters in it. idk what you're using in PHP as your delimiter but this worked for me:

$strBase64 = 'SMZiVTAMizngWa5Yg2Xp0F3Coy4cIsLB6mru2rLhxnvS2SC\/rm9pgPVLdA\/hp+1TIbzHZqjc2lnP\nkvzh797WlA==\n';
$strBase64 = str_replace(['\/', '\n'], ['/', ''], $strBase64);

If you're using double quotes instead of single quotes do this:

$strBase64 = "SMZiVTAMizngWa5Yg2Xp0F3Coy4cIsLB6mru2rLhxnvS2SC\/rm9pgPVLdA\/hp+1TIbzHZqjc2lnP\nkvzh797WlA==\n";
$strBase64 = str_replace(['\/', "\n"], ['/', ''], $strBase64);

answered Dec 1, 2018 at 20:52

neubert

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Samrat Thapa · Accepted Answer · 2022-11-16 11:34:25Z

0

$rsa = new RSA();
  $rsa->setEncryptionMode(RSA::ENCRYPTION_OAEP);
  $ciphertext = base64_decode($string);
  $rsa->setMGFHash('sha1');
  $rsa->setHash('sha256');
  $rsa->loadKey($pkey); // public key
  $output = $rsa->decrypt($ciphertext);
 return $output;

answered Nov 16, 2022 at 11:34

Samrat Thapa

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