How to do ECB mode when dealing with RSA? I dont understand it. The Aadhar authentication doc (http://uidai.gov.in/images/FrontPageUpdates/aadhaar_authentication_api_1_6.pdf Page 33) says that we have to use RSA/ECB/PKCS1Padding but I am not finding any references to mode when dealing with RSA.

  • We generate a AES-256 session key on server and send to client. (We forget the session key)
  • Client encrypts his data block with symmetric AES/ECB/PKCS7Padding (using cryptojs)
  • Client encrypts his session key with 2048-bit Aadhar public key using asymmetric algorithm (RSA/ECB/PKCS1Padding)
  • Client also calculates HMAC of Data Block
  • Client sends us the three fields, the server fills in other data and sends to Aadhar server

So we need to do RSA/ECB/PKCS1Padding in the web client in Javascript. CryptoJS doesnot support RSA so you can use any other library

If somebody can tell me if the Forge library's example

var encrypted = publicKey.encrypt(bytes, 'RSAES-PKCS1-V1_5');

uses ECB or not. There are references to RSA/ECB/OAEPWithSHA-256AndMGF1Padding but I need PKCS#1 padding

Can you suggest me any other library or tell me proper code in Forge?

If I can do this in PHP on server side then also I can send session key and encrypted session key to client and then forget the session key.

I donot understand much cryptography but understand the terms somewhat.

  • I'm not saying that this is THE answer but I think that your framework works for both type of ciphers and thus requires a mode before allowing you to specify a padding scheme. In that case ECB applied to asymetric encryption would mean "do nothing"... Eg. See in Java docs.oracle.com/javase/7/docs/api/javax/crypto/Cipher.html
    – Cerber
    Commented Nov 4, 2015 at 16:39

1 Answer 1


ECB doesn't even make sense in the context of RSA. It's a mode of operation for symmetric ciphers like AES. More info:


PKCS1Padding, however, does apply to RSA. And you're right - that likely means RSAES-PKCS1-V1_5. For the PHP side you can use phpseclib. eg.


$rsa = new Crypt_RSA();
$rsa->loadKey('...'); // public key

$plaintext = '...';

$ciphertext = $rsa->encrypt($plaintext);

$rsa->loadKey('...'); // private key
echo $rsa->decrypt($ciphertext);

URL: http://phpseclib.sourceforge.net/

  • See my comment in the question : I think it's because his frameworks makes it mandatory to specify a mode before the padding type (although it is useless)
    – Cerber
    Commented Nov 4, 2015 at 16:41

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