code: function(recipient, privKey) {
        if(msg.encryptedContent.key === undefined && recipient !== undefined &&
          privKey !== undefined) {
          switch(recipient.encryptedContent.algorithm) {
            case forge.pki.oids.rsaEncryption:
            case forge.pki.oids.desCBC:
              var key = privKey.decrypt(recipient.encryptedContent.content);
              msg.encryptedContent.key = forge.util.createBuffer(key);
              break;
  
            default:
              throw new Error('Unsupported asymmetric cipher, ' +
                'OID ' + recipient.encryptedContent.algorithm);
          }
        }
  
        _decryptContent(msg);
      }
docs: Decrypt enveloped content
  
  @param recipient The recipient object related to the private key
  @param privKey The (RSA) private key object