CODEWITHSUNDEEP
javaphpandroidopensslrsa
ashutosh
ashutosh

Reputation: 649

Android KeyPairGenerator + php openssl_public_encrypt

I have a client (android device) that generates a public+private key pair. It sends the public key to a server and the server should encrypt some data using the public key and return it so the client can decrypt it using the private key later. My php code logs a warning stating that the public key I am providing it is invalid.

On the device side, I generate the key pair as follows -

KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(256);
KeyPair kp = kpg.generateKeyPair();
PublicKey publicKey = kp.getPublic();

I then base64 encode and POST it -

String urlParameters = "productID=" + productID + "&publicKey="
                + URLEncoder.encode(Base64.encodeToString(publicKey.getEncoded(),
                        Base64.DEFAULT)); // without the URLEncoder, the + signs
                                          // are turned into spaces

On the server side, I extract the publicKey from the POST parameters and try to use it for encoding some data -

$publicKey = $_POST['publicKey'];
$encryptedData = '';
$productData = 'test test test';
openssl_public_encrypt($productData, $encryptedData, $publicKey);

This ends up erroring out with the following in the log -

PHP Warning:  openssl_public_encrypt(): key parameter is not a valid public key

I have also tried adding prefix and suffix to the public key before using it for encryption but that did not help either -

$publicKey = "-----BEGIN PUBLIC KEY-----\r\n" . $publicKey . "\r\n-----END PUBLIC KEY-----";

Have broken my head over this for a while and none of the suggestions I came across online seem to help. Any thoughts would be most helpful!

Upvotes: 1

Views: 1215

Answers (1)

ashutosh
ashutosh

Reputation: 649

Managed to solve the issue finally by making 2 changes -

  1. Had to use the Base64.NO_WRAP flag instead of Base64.DEFAULT on the Java side.
  2. Added the prefix/suffix in php after chunk splitting - $publicKey = "-----BEGIN PUBLIC KEY-----\r\n" . chunk_split($publicKey) . "-----END PUBLIC KEY-----";

Upvotes: 1

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