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User Trailers

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User trailers, except for the CHK trailer, are optional and when present, occur in the following order:

Trailer code Name
MAC Message Authentication Code
PAC Proprietary Authentication Code
CHK Checksum
TNG Training
PDE Possible Duplicate Emission

  • Message Authentication Code (MAC) Trailer. Allows authentication by the receiving user. The MAC trailer is followed by an authentication result. This trailer is mandatory for most user-to-user message categories within the FIN application.

    When the FIN Copy Service is used, a PAC trailer (if present) follows the MAC trailer. The following code is an example of a MAC trailer:

    {MAC:<authentication-result>}  
where <authentication-result> = 8!h

  • Proprietary Authentication Code (PAC) Trailer. The PAC trailer is used within the FIN Copy service only when using the double authentication option. Block 5 of FIN user-to-user messages include the PAC trailer immediately after the MAC trailer, if present. This result is calculated on the extracted fields of Block 4 of the message, the value of field 115, if present, and the <authentication-result> of the MAC trailer for Copy Services with double authentication.

    As a result, the end-of-block indicator (CrLf-) is included in the PAC calculation and the fields are defined as follows:

    • The first four characters are CrLf:

    • The field and the delimiter are present, that is, 32A:, 20:, and so on.

    • All subfields and their delimiters are present.

      The following code is an example of the PAC trailer format:

    {PAC:[<authentication-result>]}  
where <authentication-result> is mandatory on input messages only and  
<authentication-result> = 8!h

  • CHK (Checksum) Trailer (mandatory for all FIN messages)

    The CHK trailer is mandatory for all FIN messages and is computed based upon the receiver's address (12 characters with the ninth character replaced by X plus the text block). This trailer allows the system and the CBT to check that messages are not corrupted due to a system malfunction or an undetected transmission error.

    The following code is an example of the CHK trailer format:

    {CHK:<checksum-result>}  
where <checksum-result> = 12!h

See Also

Working with Schemas