im failing to decrypt the response from the whatsapp flow, and im using php, codeigniter 4 with the phpseclib3 library, and below is my sample code:

private function decryptRequest($body, $privatePem) {     $encryptedAesKey   = base64_decode($body['encrypted_aes_key']);     $encryptedFlowData = base64_decode($body['encrypted_flow_data']);     $initialVector     = base64_decode($body['initial_vector']);     $rsa = RSA::load($privatePem)         ->withPadding(RSA::ENCRYPTION_OAEP)         ->withHash('sha256')         ->withMGFHash('sha256');                          $decryptedAesKey = $rsa->decrypt($encryptedAesKey);              if (!$decryptedAesKey) {         throw new Exception('Decryption of AES key failed.');     }          $aes = new AES('gcm');     $aes->setKey($decryptedAesKey);     $aes->setNonce($initialVector);          $decrypted = $aes->decrypt($encryptedFlowData);     if (!$decrypted) {         throw new Exception('Decryption of flow data failed.');     }          return [         'decryptedBody' => json_decode($decrypted, true),         'aesKeyBuffer' => $decryptedAesKey,         'initialVectorBuffer' => $initialVector,     ]; }

and im getting the Ciphertext representative too long error on this line: $decryptedAesKey = $rsa->decrypt($encryptedAesKey);

I have tried to refer to the docementation here https://developers.facebook.com/docs/whatsapp/cloud-api/reference/whatsapp-business-encryption

Tag:whatsapp-cloud-api, whatsapp-flows

3 comments.

  1. gafi

    I have some questions to help debug:

    Did you use a passphrase while generating the private key? You don't seem to be using it in the code above Did you recently update the public key and you're testing on a phone? If so, the old public key might be cached on the phone. Return HTTP code 421 from the endpoint to refresh the key on the client as mentioned in the docs https://developers.facebook.com/docs/whatsapp/flows/reference/error-codes#endpoint_error_codes Are you able to preview with the endpoint in the Flow Builder? https://developers.facebook.com/docs/whatsapp/flows/introduction/flowbuilderui

    There's a full code example in PHP for decryption here. You seem to be missing a few steps after the one that's currently failing, so please refer to the example https://developers.facebook.com/docs/whatsapp/flows/guides/implementingyourflowendpoint#php-slim-example

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    1. iam_furanki

      1. on the passpharase, yes, i pass it here $rsa = RSA::load($privatePem,'passphrase'); 2. I had to reverify my key and all seems well 3. Are you able to preview with the endpoint in the Flow Builder? , Yes im able to do that

      Reply
    2. gafi

      on #2, if you recently updated the key and it's working on builder but not on phone, then it is likely caching an older key. Can you try on a different phone? if you return http error code 421 from the endpoint, it will force the phone to refresh the key

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