nric.py

# https://en.wikipedia.org/wiki/National_Registration_Identity_Card
# http://www.ngiam.net/NRIC/
# http://www.ngiam.net/NRIC/NRIC_numbers.pdf

import random

weights = [2, 7, 6, 5, 4, 3, 2]
local_alphas = 'JZIHGFEDCBA'
foreign_alphas = 'XWUTRQPNMLK'

alt_weights = [9, 4, 5, 6, 7, 8, 9]
alt_local_alphas = 'JABCDEFGHIZ'


def checksum_alpha(digits, init_alpha='S'):
    # sanity check
    assert len(digits) == 7
    # dot product
    checksum = sum(weight * int(digit) for weight, digit in zip(weights, digits))
    # offset based on initial letter
    if init_alpha.lower() in 'sf':
        checksum += 0
    elif init_alpha.lower() in 'tg':
        checksum += 4
    else:
        pass
    # return from appropriate alphabet
    if init_alpha.lower() in 'st':
        return local_alphas[checksum % 11]
    elif init_alpha.lower() in 'fg':
        return foreign_alphas[checksum % 11]
    else:
        return None


def validate(ic):
    # cleanup
    ic = ic.strip()
    # catch malformed input
    try:
        return ic[8] == checksum_alpha(ic[1:8], ic[0])
    except:
        return None


def generate(year=None, local=None):
    # randomize unknown year
    if year is None:
        year = random.choice(range(1901, 2020))
    else:
        assert 1799 < year < 2100
    # randomize unknown local/foreign
    if local is None:
        local = bool(random.getrandbits(1))
    # first two digits
    if local:
        if year > 1967:
            digits = str(year)[-2:]
        else:
            # in reality there's probably some distribution over the other digits too
            digits = random.choice('01') + str(random.randint(0, 9))
    else:
        # much is unknown about fins, this seems incorrect
        if year > 2008:
            digits = random.choice('45678901') + str(random.randint(0, 9))
        else:
            digits = random.choice('23') + str(random.randint(0, 9))
    # now append more digits
    digits += str(random.randint(0, 99999)).rjust(5, '0')
    # find first alphabet
    init_alpha = '------------------sst' if local else '------------------ffg'
    init_alpha = init_alpha[year // 100]
    # last alphabet and capitalize
    final_alpha = checksum_alpha(digits, init_alpha)
    out = init_alpha + str(digits) + final_alpha
    return out.upper()

if __name__ == '__main__':
    print validate('S0000001I')  # Yusof bin Ishak
    print validate('S0000002G')  # Lee Kuan Yew
    print validate('S0000003E')  # Kwa Geok Choo
    print checksum_alpha('9876543', init_alpha='S')
    print checksum_alpha('3456789', init_alpha='G')
    print generate(2019, True)