Send the Signed and Encrypted key to your partner

The data can then be sent to your partner using any mechanism you like. Since the data is encrypted and signed it is a very secure package and since you will only use the symmetric passphrase once its physical security is not an issue either. The recommended method would be to use a web service running over https (SOAP). The SOAP message should include the encrypted payload and optionally could include the signed and encrypted symmetric passphrase and your public certificate as attachments similar to my example below.

MIME-Version: 1.0
Content-Type: Multipart/Related; boundary=MIME_boundary; type=text/xml;
        start="<securemsg>"
Content-Description: This is the optional message description.

--MIME_boundary
Content-Type: text/xml; charset=UTF-8
Content-Transfer-Encoding: 8bit
Content-ID: <securemsg>

<?xml version='1.0' ?>
<SOAP-ENV:Envelope
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
<SOAP-ENV:Body>
..
<theSignedData href="myPriv.xml.ase128"/>
<thePublicCert href="cln-pubcert.pem"/>
<theSymmetricKey href="passphrase.sig.enc"/>
..
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>
--MIME_boundary
Content-Type: application/encoded-data
Content-Transfer-Encoding: base64
Content-ID: <myPriv.xml.ase128>

...base64 AES encoded xml data
--MIME_boundary
Content-Type: application/public-certificate
Content-Transfer-Encoding: base64
Content-ID: <cln-pubcert.pem>

...PEM version of public certificate
--MIME_boundary
Content-Type: application/symmetric-key
Content-Transfer-Encoding: base64
Content-ID: <passphrase.sig.enc>

...PEM version of Signed and Encrypted symmetric passphrase
 --MIME_boundary
        

If you are not planning to reuse the passphrase for subsequent transmissions then it is safer to remove it then to leave it on your system.

			$ rm passphrase-$$ passphrase-$$.sig passphrase-$$.sig.enc passphrase.sig.enc