ISO 7064

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Overview

ISO 7064 specifies a set of check character systems capable of protecting strings against errors which occur when people copy or key data.

The check character systems specified in ISO/IEC 7064:2002 can detect:

• all single substitution errors (the substitution of a single character for another, for example 4234 for 1234);
• all or nearly all single (local) transposition errors (the transposition of two single characters, either adjacent or with * one character between them, for example 12354 or 12543 for 12345);
• all or nearly all shift errors (shifts of the whole string to the left or right);
• a high proportion of double substitution errors (two separate single substitution errors in the same string, for example 7234587 for 1234567);
• a high proportion of all other errors.

Function StrMOD97

The function StrMOD97 can encode and verify a checksum in accordance with ISO 7064, modulo 97-10.

function StrMOD97(s: String): integer;
// Pre-condition: s can only contain digits, otherwise this function will raise an exception.
// See https://wiki.freepascal.org/International_Bank_Account_Number for handling of non digits
const
  modu = 97;
var
  sx: String;
  isx, ic, p: Integer;
begin
   p := Length( s );
   while ( p > 9 ) do
     begin
       sx := Copy( s, 1, 9 );
       Delete( s, 1, 9 );
       isx := StrToInt( sx );
       ic := isx mod modu;
       s := IntToStr( ic ) + s;
       p := Length( s );
     end;
   isx := StrToInt( s );
   if isx >= modu
     then ic := isx mod modu
     else ic := isx;
  result := ic;
end;

See also

• International Bank Account Number an example of usage of the above function handling both digits and non-digits.