ChrisThilges

Documentation:
trustbearer-FASC-N-question.html
TIG_SCEPACS_v2.2.pdf
src: index.php.zip

Smart Card Enabled PACS (Physical Access Control Systems):
The Federal Agency Smart Credential Number (FASC-N) is an identifier used as the primary identification string on all government issued credentials. (see sections 6.2-6.3, pages 25-28, of the TIG-SCEPACS for reference). It is felt necessary that the process for assignment of these numbers–while conducted in a decentralized manner–be developed centrally to secure facilities under the control of federal agencies across the country and around the globe.

FASC-N Encoding:
Data on the FASC-N is encoded using a process called Binary Coded Decimal (BCD). It uses 5 bits per character (4 data bits and 1 parity bit) and results in a 16-character set. Encoding the full 40-character FASC-N in BCD digit format results in 200 bits of information. Rather than transmit the data one character at a time, the data can be packed such that each transmitted byte contains 8 meaningful bits (e.g. the full 5 from Character One plus the first 3 from the Character Two). These 200 bits can thus be transmitted in the form of 25 bytes (200 bits divided by 8 bits per byte).
FASC-N figure7 contains details of the BCD 4-Bit Decimal Format with Odd Parity Download Hover

Decimal: [0032-0001-092446-0-1-1112223333112232]
Hexadecimal: D0 43 94 58 21 0C 2C 19 A0 84 6D 83 68 5A 10 82 10 8C E7 39 84 10 8C A3 FC
Binary: 11010 00001 00001 11001 01000 10110 00001 00001 00001 10000 10110 00001 10011 01000 00100 00100 01101 10110 00001 10110 10000 10110 10000 10000 10000 01000 01000 01000 11001 11001 11001 11001 10000 10000 01000 01000 11001 01000 11111 11100

FASC-N Field Definitions
Each 5 bit chunk of the 40 decimal string can be translated into fields specifying agency and user identification codes.

FASC-N figure6 contains detailed FASC-N field definitions: Download Hover