Standard Transfer Specification Association
Standard Transfer Specification Association


In mathematics and computer science, an algorithm is a finite sequence of well-defined, computer-implementable instructions, typically to solve a class of specific problems or to perform a computation (Wikipedia).

To the STSA's knowledge, none of its algorithms have ever been compromised.

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)

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

  1. ​Primary Account Number (PAN), made up of the International identification number (IIN), and the Decoder Reference Number (DRN)
  2. Key Type (KT)
  3. Tariff index (TI)
  4. Key revision number (KRN)
  5. Vending key (VK)
  6. Supply group code (SGC)
  7. Base date (DKGA04 only)

DKGA's in use:

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

​​​Encryption/Decryption Algorithm (EA)

Encryption: An algorithm used to render readable data into un-readable data by making use of public or secret keys.

Decryption: An algorithm used to render un-readable data into readable data by making use of secret keys.


The STS standard supports the following encryption algorithms (EA):






STA 64-bit DES based

Legacy, still in use

02, 04


MISTY – 128-bit key, 64-bit payload

High security algorithm.


Real & Sample Tables

The STA encryption algorithm 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, STS600-4-2