คุณสมบัติ EncryptionPassword

property EncryptionPassword: WideString;

The write path emits a BIFF8 FILEPASS record ($002F) immediately after the workbook BOF and RC4-encrypts every subsequent record body. The wire format is vMajor=1, vMinor=1 ("Office 97/2000 Compatible" encryption). 16-byte Salt and Verifier are generated through Windows CryptGenRandom rather than Pascal Random. Block-key re-derivation at every 1024-byte boundary is preserved so large workbooks, SST CONTINUE chains, and multi-sheet streams encrypt correctly

Encryption applies to BIFF8 (xlExcel97) only — the BIFF5 save path remains plaintext. An empty EncryptionPassword keeps the legacy plaintext output and is the default, so existing applications that never call the setter are unaffected

Security note: BIFF8 RC4 with vMajor=1/vMinor=1 uses a 40-bit key, which is considered broken by 2025 standards. Use this feature for compatibility with Excel's classic password-protection UI, not for confidentiality of sensitive data. For real security, prefer XLSX output with AES

This example saves a password-protected .xls file