Clean-room import of Excel 97-2003 workbooks from the public [MS-CFB] and
[MS-XLS] specifications: compound-file streams (FAT, mini FAT, directory
tree), the BIFF8 Workbook stream with Continue records, shared strings,
all cell records, formulas decoded from Ptg tokens (shared and array
formulas, 3-D refs, names, add-in/newer functions by name) with cached
results, number formats, the 1904 date system, merges, column widths, row
heights, defined names and print areas/titles. Encrypted (FILEPASS) and
BIFF5 files are refused with a clear message; everything else is skipped
with a warning. .xls opens as a new unsaved workbook (Save As .xlsx).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Every legacy .xls/.doc is a CFB/OLE2 file, so the signature alone isn't encryption. Walk the
compound file's directory (bounds-checked, bounded loops; raw UTF-16 scan when the structure
is unreadable) and report Encrypted only for an EncryptedPackage/EncryptionInfo stream;
other compound files are LegacyBinary with a "save as .xlsx" message. Tests build CFB bytes
in code.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
