The FASC-N (Federal Agency Smart Credential Number) is a unique identifier used in the U.S. federal government's Personal Identity Verification (PIV) system. It is a critical component of the PIV credential, as defined in federal standards like FIPS 201 and related documents.

The FASC-N is comprised of a total of 40 characters encoded as BCD (Binary Coded Decimal) digits. It consists of 32 numeric characters of meaningful data. In addition, it contains a single numeric character called the Longitudinal Redundancy Check (LRC) that serves as a means by which a reader can mathematically validate its reading of the preceding data. In keeping with the accepted practices for magnetic stripe reading, the FASC-N shall include 7 additional characters that tell a magnetic stripe reader where meaningful data begins and ends as well as where blocks of data within the string of numbers are separated. 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.

Key Features of the FASC-N:

• Unique Identifier: The FASC-N uniquely identifies a PIV credential holder across the federal government, ensuring no duplication of identities.
• Structure: The FASC-N is a 25-field, fixed-length numeric string, divided into several segments. These segments encode specific pieces of information, such as:

	Field Name Length	Length (BCD Digits)	Field Description
Uniquely Identifies Card	Agency Code	4	Identifies the government agency issuing the credential
	System Code	4	Identifies the system the card is enrolled in and is unique for each site
	Credential Number	6	Encoded by the issuing agency. For a given system no duplicate numbers are active.
	Credential Series (Series Code)	1	This field is used to reflect major changes or upgrades to the system or credential type.
	Individual Credential Issue	1	Extends the Credential Number. Initially encoded as 1. It will be incremented if a card is replaced due to loss or damage.
Uniquely Identifies Card Holder	Person Identifier	10	Numeric Code used by the identity source to uniquely identify the token carrier (e.g. DoD EDI PN ID…TWIC Credential No….NASA UUPIC).
	Organization Category	1	Type of Organization (1-Federal Government, 2-State Government, 3-Commercial Enterprise, 4- Foregin Government) the individual is affiliated with.
	Organization Identifier	4	The Identifier that identifies the organization (OC=1-NIST Agency, OC=2-State Code, OC=3-Company Code, OC=4-Numeric Country Code) the individual is affiliated. with.
	Person/Organization Association Category	1	Indicates the affiliation type (1= Emp, 2=Civil, 3=Ex Staff, 4=Uniform Svc, 5=Contractor, 6=Organizational Affiliate, 7= Organizational Beneficiary) the individual has with the Organization.

• Standardization: It follows a standardized format specified in NIST SP 800-73, ensuring consistency across government agencies.
• Use in Authentication:
• The FASC-N is embedded within the PIV card's chip as part of the Cardholder Unique Identifier (CHUID) or within the X.509 certificate on the card.
• It is used during physical and logical access authentication processes.
• Derived Credentials: In systems supporting derived PIV credentials (e.g., Derived FIDO2 Credentials), the FASC-N may be used as part of the linkage to the original PIV card.
• Security Considerations: While the FASC-N facilitates identification and authentication, it is sensitive information. Its exposure or misuse could lead to security risks, such as impersonation.