GnuPG message encryption system - encryption

Question

I want to build a message encryption system where users will send message in a encrypted format. I am using GnUPG.I got help from http://www.php.net/manual/en/gnupg.installation.php to install the GnUPG. After install in the server I create the public and private keyring by following code
$GeneratedKey = $gpg->GenKey($name, $comment, $email, $passphrase,$ExpireDate, $KeyType, $KeyLength,$SubkeyType, $SubkeyLength );
function GenKey($RealName, $Comment, $Email, $Passphrase = '', $ExpireDate = 0, $KeyType = 'DSA', $KeyLength = 1024, $SubkeyType = 'ELG-E', $SubkeyLength = 1024)
{
// validates the keytype
if (($KeyType != 'DSA') && ($KeyType != 'RSA')) {
$this->error = 'Invalid Key-Type, the allowed are DSA and RSA';
return false;
}
// validates the subkey
if ((!empty($SubkeyType)) && ($SubkeyType != 'ELG-E')) {
$this->error = 'Invalid Subkey-Type, the allowed is ELG-E';
return false;
}
// validate the expiration date
if (!preg_match('/^(([0-9]+[dwmy]?)|([0-9]{4}-[0-9]{2}-[0-9]{2}))$/', $ExpireDate)) {
$this->error = 'Invalid Expire Date, the allowed values are <iso-date>|(<number>[d|w|m|y])';
return false;
}
// generates the batch configuration script
$batch_script = "Key-Type: $KeyType\n" .
"Key-Length: $KeyLength\n";
if (($KeyType == 'DSA') && ($SubkeyType == 'ELG-E'))
$batch_script .= "Subkey-Type: $SubkeyType\n" .
"Subkey-Length: $SubkeyLength\n";
$batch_script .= "Name-Real: $RealName\n" .
"Name-Comment: $Comment\n" .
"Name-Email: $Email\n" .
"Expire-Date: $ExpireDate\n" .
"Passphrase: $Passphrase\n" .
"%commit\n" .
"%echo done with success\n";
// initialize the output
$contents = '';
// execute the GPG command
if ( $this->_fork_process($this->program_path . ' --homedir ' . $this->home_directory .
' --batch --status-fd 1 --gen-key',
$batch_script, $contents) ) {
$matches = false;
if ( preg_match('/\[GNUPG:\]\sKEY_CREATED\s(\w+)\s(\w+)/', $contents, $matches) )
return $matches[2];
else
return true;
} else
return false;
}
I encrypt by the following code
$gpg = new gnupg();
$gpg->addencryptkey($recipient);
$ciphertext = $gpg->encrypt($plaintext);
Decrypt by the following code
$gpg = new gnupg();
$gpg->adddecryptkey($recipient, $receiver_passphrase);
$plain = $gpg->decrypt($encrypted_text, $plaintext);
BY this I successfully create a folder of a username and generate private and public keyring over there and then send message in a encrypted way and decrypt by the receiver. But my main concern is I don't want to generate user public and private keyring in the server, instead I want to generate public and private keyring in users local computer..
Is it possible to generate public and private key in local computer? Because I don't want user depend on server security. Only receiver will able to decrypt the message.. Not other will able to decrypt..
thanks,

Answer 1

You can create the keys using OpenPGP.js which runs in your client's browser, store the private key somewhere with your client and send nothing but the public one to the server.
// Create new key with RSA encryption (1), 4k length for
// John Doe with password "foobar"
var keys = openpgp.generate_key_pair(1, 4096,
"John Doe john.doe#example.org", "foobar");
keys.privateKeyArmored; // Access private key
keys.publicKeyArmored; // Access public key