FAQ Security

2. Security

2.1 What components is Secuvoice based on?

Secusmart’s approach for securing your mobile calls is completely hardware-based: All security critical functions are implemented on the certified hardware. This means that the encryption algorithms, secure key exchange, and key management is tamper proof. Moreover, secret keys never leave the secure hardware environment and are therefore not exposed to interception.    
The trusted hardware is an EAL5+ certified crypto controller from NXP. Together with up to 1GB of flash memory the crypto controller is integrated in the Secusmart Security Card, which looks and feel like a standard microSD card. Flash memory and crypto functions are independent from each other.
The crypto algorithm was developed by the German Federal Office for Information Security (BSI). The package consisting of a NXP crypto controller and the BSI crypto algorithm and will also be deployed for end-to-end encryption services in the mobile radio network for public safety organizations in Germany (BOS-Digital).

2.2 How is the key agreement carried out during call setup?

Prior to symmetric-key encryption of the voice, both call parties need to agree on a shared secret key. Secuvoice uses a variant of the well-established Diffie-Hellman key agreement protocol, which is based on elliptic curve cryptography. Elliptic Curve Diffie-Hellman (ECDH) guarantees both highly secure and ultra fast key exchange over insecure mobile communication channels.

2.3 How much time is required for the key agreement?

The advantage of ECDH as compared to implementations of Diffie-Hellman based on integer factorization cryptography as, for instance, RSA, is that it allows for shorter key lengths and faster computation, while being equally secure.
In practice, key agreement takes only a few moments at a security level comparable to Diffie-Hellman with 2048 bit key-length (based on best known attacks on RSA, DSA, and Diffie-Hellman at 2048 bits).

2.4 What type of encryption is used during the secure call?

To secure voice calls end-to-end, speech is encrypted using AES (Advanced Encryption Standard) with 128bit key-length. Today, AES is regarded as the most secure and computationally fastest algorithm for symmetric-key encryption. It has been analyzed extensively and was adopted as the encryption standard by the U.S. Government.
End-to-end security means that both encryption and decryption of the voice takes place inside the mobile phone (or more precisely inside the crypto controller). The voice traverses the communication network fully encrypted from one end to the other. Your call is therefore end-to-end secure against being overheard both on the air interface and within the fixed line network.

2.5 Why does Secuvoice authenticate the exchanged keys?

To over-come the notorious “man-in-the-middle” attacks on the Diffie-Hellman key agreement protocol, Secuvoice uses an authenticated version of this protocol. Key authentication in Secuvoice is based on the use of certificates as part of a PKI (Public Key Infrastructure).
Secusmart operates a dedicated PKI for Secuvoice and acts as the certificate authority (CA). Each Secusmart Security Card is equipped with a user certificate including a digital signature of the CA, which combines the public key with the cryptographic identity of the user (see user authentication below). The user certificate is securely stored inside the trusted hardware during production of the Secusmart Security Card.
During the key agreement, both parties verify the received signature, thereby validating the public key of the other party. The signature cannot be forged without the secret key created by the CA.
As a result of using the authenticated Diffie-Hellman key agreement, Secuvoice is inherently safe against “man-in-the-middle” attacks. Secuvoice does not need to rely on verbal comparison of hash-codes or similarly odd procedures for key authentication.

2.6 How does Secuvoice ensure the authentication of the other party?

Secuvoice is the world’s first solution that secures mobile voice calls by certificate based user authentication. That is, communication partners are identified by their cryptographic identity, also called “Fingerprint”, which is contained in the user certificate.
User authentication, much like key authentication, means that both parties can verify the signature enclosed in the received user certificate, and thereby authenticate the identity of the other party. Again, the signature cannot be forged without the secret key created by the CA.
With Secuvoice you are no longer vulnerable to caller ID spoofing, since the caller identification is not based on the telephone number, which can be easily forged and is therefore insecure.

2.7 Secuvoice introduces the concept of domain names – what is the purpose of the domain names?

Secuvoice features a Domain Name system for secure telephony, similar to the domain name system used on the Internet. If you are a using Secuvoice for securing mobile voice communication within an organization (e.g. a company), you can register a domain name, which would typically be the name of the organization.
The domain name is part of the certificates of all users who belong to that particular domain and hence an unchangeable part of their cryptographic identity. The domain name enhances user authentication, as each user identifies him/herself unforgeably as a member of a particular organization described by the domain name.

2.8 How does Secusmart guarantee the intactness of the Secusmart Security Card?

Your new Secusmart Security Card will be delivered with an electronic seal called Zero-PIN. Like any other seal it does not prevent others breaking it, i.e., accessing your Secusmart Security Card before you, but it gives proof of its integrity. You can be absolutely sure that your Secusmart Security Card is still pristine or whether someone has tampered with it.
The Zero PIN can be entered only once to unlock the Secusmart Security Card for the first time. Immediately after that you will be asked to enter a new, arbitrary PIN. The PIN is a secret which only you should know, which protects your Secusmart Security Card against misuse and unauthorized access by others.

Important note: Never make the Secusmart Security Card available to any other person as it contains confidential information!