| """Rule-based field validators for document fraud detection. |
| |
| Pure standard library. Every validator returns (ok: bool, reason: str). |
| Rules encode publicly documented validity constraints: |
| - SSN structure per SSA randomization (area 001-899 excluding 666, |
| group 01-99, serial 0001-9999; 000/666/9xx areas, 00 groups and |
| 0000 serials have never been issued) |
| - ICAO Doc 9303 TD3 (passport) MRZ check digits, weights 7-3-1 |
| """ |
| import datetime as _dt |
| import re |
|
|
| _SSN_RE = re.compile(r"^(\d{3})-(\d{2})-(\d{4})$") |
|
|
|
|
| def validate_ssn(value): |
| if value is None: |
| return False, "missing" |
| m = _SSN_RE.match(value.strip()) |
| if not m: |
| return False, "malformed" |
| area, group, serial = (int(x) for x in m.groups()) |
| if area == 0 or area == 666 or 900 <= area <= 999: |
| return False, "invalid_area" |
| if group == 0: |
| return False, "invalid_group" |
| if serial == 0: |
| return False, "invalid_serial" |
| return True, "ok" |
|
|
|
|
| _DATE_FORMATS = ("%m/%d/%Y", "%Y-%m-%d", "%d.%m.%Y", "%Y%m%d") |
|
|
|
|
| def parse_date(value): |
| for fmt in _DATE_FORMATS: |
| try: |
| return _dt.datetime.strptime(value.strip(), fmt).date() |
| except (ValueError, AttributeError, TypeError): |
| continue |
| return None |
|
|
|
|
| def validate_date(value, must_be_past=False, reference=None): |
| d = parse_date(value) if isinstance(value, str) else None |
| if d is None: |
| return False, "unparseable" |
| ref = reference or _dt.date.today() |
| if must_be_past and d > ref: |
| return False, "future_date" |
| return True, "ok" |
|
|
|
|
| _NAME_RE = re.compile(r"^[A-Z][A-Z' -]{0,63}$", re.IGNORECASE) |
|
|
|
|
| def validate_name(value): |
| if not value or not value.strip(): |
| return False, "missing" |
| if not _NAME_RE.match(value.strip()): |
| return False, "bad_characters" |
| return True, "ok" |
|
|
|
|
| _MRZ_ALPHABET = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" |
|
|
|
|
| def mrz_check_digit(field): |
| total = 0 |
| for i, ch in enumerate(field): |
| v = 0 if ch == "<" else _MRZ_ALPHABET.index(ch) |
| total += v * (7, 3, 1)[i % 3] |
| return str(total % 10) |
|
|
|
|
| def validate_mrz_line2(line): |
| line = (line or "").strip() |
| if len(line) != 44: |
| return False, "bad_length" |
| if not re.match(r"^[A-Z0-9<]{44}$", line): |
| return False, "bad_characters" |
| sex = line[20] |
| if not (sex == "<" or sex in "MF"): |
| return False, "bad_sex" |
| for part, label in ((line[13:19], "dob"), (line[21:27], "exp")): |
| if not re.match(r"^\d{6}$", part): |
| return False, "bad_" + label + "_format" |
| mm, dd = int(part[2:4]), int(part[4:6]) |
| if not (1 <= mm <= 12 and 1 <= dd <= 31): |
| return False, "bad_" + label + "_value" |
| composite = line[0:10] + line[13:20] + line[21:43] |
| checks = ( |
| (9, line[0:9], "pno"), |
| (19, line[13:19], "dob"), |
| (27, line[21:27], "exp"), |
| (42, line[28:42], "personal"), |
| (43, composite, "composite"), |
| ) |
| for pos, material, name in checks: |
| if line[pos] != mrz_check_digit(material): |
| return False, "check_digit_" + name |
| return True, "ok" |
|
|
|
|
| def parse_date_any(value): |
| return parse_date(value) |
|
|
|
|
| def validate_document(fields, reference=None): |
| findings = [] |
| if "document_number" in fields: |
| ok, why = validate_ssn(fields["document_number"]) |
| if not ok: |
| findings.append("document_number:" + why) |
| if "name" in fields: |
| ok, why = validate_name(fields["name"]) |
| if not ok: |
| findings.append("name:" + why) |
| for key in ("date_of_birth", "issue_date", "expiry_date"): |
| if key in fields: |
| ok, why = validate_date(fields[key], reference=reference) |
| if not ok: |
| findings.append(key + ":" + why) |
| ref = reference or _dt.date.today() |
| dob = parse_date(fields.get("date_of_birth", "")) |
| if dob and dob > ref: |
| findings.append("dob_in_future") |
| if dob and (ref - dob).days > 150 * 365: |
| findings.append("implausible_age") |
| issued = parse_date(fields.get("issue_date", "")) |
| expiry = parse_date(fields.get("expiry_date", "")) |
| if issued and expiry and expiry <= issued: |
| findings.append("expiry_before_issue") |
| if "mrz_line2" in fields: |
| ok, why = validate_mrz_line2(fields["mrz_line2"]) |
| if not ok: |
| findings.append("mrz:" + why) |
| return findings |
