class SmartId::Utils::VerificationCodeCalculator

Public Class Methods

calculate(digest) click to toggle source

The Verification Code (VC) is computed as:

integer(SHA256(hash)) mod 10000

where we take SHA256 result, extract 2 rightmost bytes from it, interpret them as a big-endian unsigned short and take the last 4 digits in decimal for display.

SHA256 is always used here, no matter what was the algorithm used to calculate hash.

# File lib/smart_id/utils/verification_code_calculator.rb, line 14
def self.calculate(digest)
  rightmost_bytes = digest[-2..-1]
  int = rightmost_bytes.unpack('n*')[0]
  paddable_string = (int % 10000).to_s.chars.last(4).join
  pad = 4 - paddable_string.length
  
  "0" * pad + paddable_string
end