Checkdigits for US Federal Identifiers

This repo contains illustrative code on how checkdigits could be added to existing US national identifier types. These are types are:

• SSN - Social Security Number
• ITIN -Individual Tax Identification Number
• FEIN - Federal Employer Identification Number

This library uses Luhn with a provenance prefix for each type. See the blog article here: https://transparenthealth.org/upgrading-ssn-checkdigit-proposal.html for more information.

Command Line Usage

Generate a checkdigit

Generate a checkdigit for an FEIN 99-1234567:

python generate_id_luhn.py 991234567 FEIN

Output:

3001009912345673

Generate a checkdigit for an SSN 123-45-6789:

python generate_id_luhn.py 123456789 SSN

Generate a checkdigit for an ITIN 9XX-7X-XXXX:

python generate_id_luhn.py 9XX7XXXX ITIN

Verify a checkdigit

Verify an FEIN with checkdigit 3001009912345673:

python verify_id_luhn.py 3001009912345673 FEIN

Verify an SSN with checkdigit:

python verify_id_luhn.py 1234567891 SSN

How It Works

The prefix is placed in front of the 9 digit number before calculating the checkdigit. Here is some Python code to illustrate:

from luhn import generate

LUHN_PREFIX_SSN = "10000"
LUHN_PREFIX_ITIN = "20000"
LUHN_PREFIX_FEIN = "30000"
value = "%s991234567" % (LUHN_PREFIX_FEIN)
checkdigit = generate(value)
print("%s%s" %(value,checkdigit))

For example, an FEIN with the number 99-1234567 would be generated using the input 30000991234567, resulting in the checkdigit 3, with the resulting ID being 9912345673.