Siemens Version: 1.2 User Manual

2. Security Services 

 

 

•  Exchange of addresses of the internal networks between security modules 

•  Signalizing that a packet was rejected because it was not received via an 

IPsec tunnel. 

The learning is always initiated if a node wants to communicate with another node 

and devices located in the same subnet actively scan by ICMP messages. The 

exchange of information about found nodes is sent encrypted over the network. 

There are several certificates and keys used by the security module as described 

in the following: 

•  Firmware: In order to authenticate a new firmware for the updating process it 

is digitally signed with RSA. The private key is handled by Siemens only, the 

public key for signature verification is stored in the flash memory of each 

device. Additionally, the firmware to load is symmetrically encrypted with 

3DES. The corresponding key is also stored in the flash memory. All devices 

use the same key. If the secret 3DES key is compromised, then the device 

must be sent to Siemens where the module is supplied with a new 3DES 

key. 

•  SSL/configuration: For the communication with SSL for configuration 

purposes a server certificate with corresponding private key is issued for 

each security module. If this key is compromised or the secret key is lost, 

the administrator needs to issue a new certificate. 

•  VPN: There are network certificates issued for each VPN. The 

corresponding private key is stored on the configuration PC. Every security 

module that belongs to the VPN holds a certificate which is signed by the 

secret key of the network certificate. A security module has thus a certificate 

with private key for every VPN it belongs to. Using this certificate it 

authenticates to other security modules establishing a secure 

communication tunnel. If a key is compromised, a new certificate must be 

issued with the configuration tool. 

•  Configuration: The configuration data on the removable media is encrypted 

with AES where a global symmetric key is used. If this key is compromised, 

a new global key needs to be deployed by a firmware update. 

 

19-Aug-05 escrypt 

GmbH 

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