STS Association Wiki

Algorithms


Algorithm types

Various algorithm types exist in a STS based system:

  1. ​Algorithms used to create decoder keys from vending keys (DKGA = Decoder Key Generation ALgorithm)
  2. Encryption Algorithms used to create and/or decrypt tokens in the meter and vending system (EA = Encryption Algorithm)

 

​Decoder Key Generation Algorithm (DKGA)

​ A DKGA is an algorithm used by the security module to create a decoder key for a payment meter from various input parameters:

  1. International identification number (IIN)
  2. Decoder reference number (DRN)
  3. Key Type (KT)
  4. Tariff index (TI)
  5. Key revision number (KRN)
  6. Vending key (VK)
  7. Supply group code (SGC)
  8. Base date (DKGA04 only)

DKGA's in use:

Currently, the following DKGA's are specified:
  1. DKGA01 (64 bit DES - not reccomended for use)
  2. DKGA02 (64 bit DES - current use)
  3. DKGA03 (triple DES - not recommended for use)
  4. DKGA04 (HMAC-SHA256 - available for use. Recommended for higher levels of security)

 

​Encryption Algorithm (EA)​

​The followign encryption algorithms are specified by the IEC62055-41 specification:

  1. EA07 - the STA algoithm currently in use. This algorithm uses a 64 bit key.
  2. EA11 - the MISTY1 algorithm. This algorithm uses a 128 bit key and is recommended for higher levels of security.

 

​Real Tables

The STA encryption algorithm (EA=07) uses a set of tables for the encryption and decryption of token data. These tables are available from the STSA for members by visiting the website and applying for a copy of the tables. Sample tables are supplied in the IEC62055-41 specification for test purposes, but cannot be used for final STS compliant systems.

 

References: IEC62055-41, STS600-4-1