Sample BAT: CLAUS version 1

CLAUS is, cryptographically, a very simple form of the Diffie-Hellman secret-sharing system: it exponentiates modulo a fixed 1024-bit prime. CLAUS doesn't contain many lines of code: it relies on the popular OpenSSL cryptographic library to generate keys and to compute shared secrets. Other BAT implementors may find CLAUS useful as an illustration of the ease of writing BATs.

CLAUS++ is a similar BAT written in C++ rather than C.

Core files

     #define SECRETKEY_BYTES 256
     #define PUBLICKEY_BYTES 128
     #define SHAREDSECRET_BYTES 128

Another file, claus-1/keypair.c, defines a keypair() function that generates a secret key and a public key:

     int keypair(
       unsigned char sk[SECRETKEY_BYTES],unsigned long long *sklen,
       unsigned char pk[PUBLICKEY_BYTES],unsigned long long *pklen
     )
     {
       ...
     }

Another file, claus-1/sharedsecret.c, defines a sharedsecret() function that generates a shared secret:

     int sharedsecret(
       unsigned char s[SHAREDSECRET_BYTES],unsigned long long *slen,
       const unsigned char sk[SECRETKEY_BYTES],const unsigned long long sklen,
       const unsigned char pk[PUBLICKEY_BYTES],const unsigned long long pklen
     )
     {
       ...
     }

There's no special naming convention for the .c files and .h files other than sizes.h. All of the C functions could have been defined in one file or spread among any number of files. All of these files are automatically compiled together by the eBATS benchmarking tools.

Add-on files

• The copyrightclaims function returns 0 to indicate that there are no known copyright claims against distribution of CLAUS.
• The patentclaims function returns 0 to indicate that there are no known patent claims against use of CLAUS.
• The multiplekeycdhchance function reports the effectiveness of the best e-euro s-second k-key attack known, namely computing 1024-bit multiplicative-group discrete logarithms:

       double multiplekeycdhchance(double e,double s,double k)
       {
         return dlchance(1024,e,s,k);
       }
  

  The underlying dlchance function is part of eBATS and didn't require any work by the CLAUS programmer.
• The simplified cdhchance function reports the effectiveness of the best e-euro s-second single-key attack known.
• The fakekeyattacks function returns 0 to indicate that providing fake public keys does not save time in attacks.

One last file, claus-1/documentation.pdf, contains references and other comments for cryptographers:

... CLAUS uses a very simple form of the Diffie-Hellman secret-sharing system. Each secret key a is used to generate a public key 2^a mod p ... Beware that the speed and security of CLAUS can be improved in many ways. ...

Version