.xltx¶

Excel spans three container families keyed by extension. .xls (and .xlt) is the legacy OLE/CFB compound file carrying a BIFF8 record stream in the Workbook stream, as specified by [MS-XLS]. .xlsx/.xlsm/.xltx are OPC/ZIP packages (OOXML) containing XML parts such as xl/workbook.xml and xl/worksheets/sheetN.xml, as specified by [MS-XLSX] and [ISO/IEC 29500-1:2016]. .xlsb is also an OPC/ZIP package but its parts contain binary BIFF12 "Brt" records rather than XML, as specified by [MS-XLSB] — it shares the OOXML protection model. One wrinkle: an OOXML file that has a document-open password is not a ZIP on disk — the entire OPC package is re-wrapped in an OLE/CFB container holding \EncryptionInfo + \EncryptedPackage streams ([MS-OFFCRYPTO] §2.3.4), preserving the outer extension.

File Extensions¶

Extension	Container	Description	Password Protection Applicable?	Notes
.xls	OLE/CFB	Excel 97-2003 Worksheet (BIFF8)	Yes — XOR/RC4-MD5/RC4-CryptoAPI open, 16-bit sheet/workbook/write verifiers	Primary legacy binary format; `Workbook` stream carries BIFF8 records per [MS-XLS]
.xlt	OLE/CFB	Excel 97-2003 Template	Same as .xls	Uses the same OLE/CFB container and encryption mechanisms as .xls; saved as a template but structurally identical
.xlm	OLE/CFB	Excel 4.0 Macro Sheet	Legacy BIFF, limited encryption support	Pre-BIFF8 macro format; largely superseded by VBA macros in .xls/.xlsm
.xlsx	OPC/ZIP (or OLE/CFB when encrypted)	Excel Workbook	Yes — Standard/Agile open, ISO protection, VelvetSweatshop	Default OOXML format; when an open password is set, the OPC/ZIP is re-wrapped in an OLE/CFB container holding `\EncryptionInfo` + `\EncryptedPackage`
.xlsm	OPC/ZIP (or OLE/CFB when encrypted)	Excel Macro-Enabled Workbook	Same as .xlsx + VBA project lock	Same OPC/ZIP container and encryption as .xlsx; additionally contains `xl/vbaProject.bin` with DPB=/CMG=/GC= VBA project protection
.xltx	OPC/ZIP (or OLE/CFB when encrypted)	Excel Template	Same as .xlsx	Uses the same OPC/ZIP container and encryption as .xlsx; template variant
.xltm	OPC/ZIP (or OLE/CFB when encrypted)	Excel Macro-Enabled Template	Same as .xlsx + VBA project lock	Uses the same OPC/ZIP container and encryption as .xlsx; macro-enabled template with VBA project lock support
.xlsb	OPC/ZIP (or OLE/CFB when encrypted)	Excel Binary Workbook (BIFF12)	Same as .xlsx but protection records are binary Brt* instead of XML	OPC/ZIP package with binary BIFF12 parts per [MS-XLSB]; shares the OOXML protection model but uses BrtSheetProtection/BrtBookProtection/etc. instead of XML elements
.xla	OLE/CFB	Excel 97-2003 Add-in	Same as .xls (can be encrypted)	Legacy add-in format; uses the same OLE/CFB container and encryption mechanisms as .xls
.xlam	OPC/ZIP	Excel Macro-Enabled Add-in	Same as .xlsm	Uses the same OPC/ZIP container and encryption as .xlsm; OOXML add-in with VBA project lock support
.xll	DLL	Excel XLL Add-in (native code)	Not an Office document — no Office password protection	Native-code DLL loaded by Excel; not an Office document container, so no Office encryption or password protection applies
.xlw	Proprietary	Excel Workspace	Window layout only — no workbook data, no encryption	Stores window layout and references to workbooks, but contains no workbook data itself; no encryption or password protection mechanisms

Gate Strength Map¶

graph TD
  subgraph real ["🔴 Real Encryption — content is ciphertext"]
    XLS_XOR["XOR Obfuscation\n.xls only"]
    XLS_RC4M["RC4 + MD5 (40-bit)\n.xls only"]
    XLS_RC4C["RC4 CryptoAPI + SHA-1\n.xls only"]
    XLSX_STD["ECMA-376 Standard\nAES + SHA-1 × 50k\n.xlsx"]
    XLSX_AGILE["ECMA-376 Agile\nSHA-512 + AES-256\n.xlsx (default)"]
  end
  subgraph strip ["🟡 Strippable Verifiers — content is plaintext"]
    XLS_SHEET["Sheet Protection\n16-bit verifier\n.xls"]
    XLS_BOOK["Workbook Protection\n16-bit verifier\n.xls"]
    XLS_WRES["Write Reservation\n16-bit verifier\n.xls"]
    XLS_RANGE["Edit Ranges\n16-bit verifier\n.xls"]
    XLS_REV["Revision Protection\n16-bit verifier\n.xls"]
    XLSX_SHEET["Sheet Protection\nISO hash\n.xlsx/.xlsb"]
    XLSX_BOOK["Workbook Protection\nISO hash\n.xlsx/.xlsb"]
    XLSX_WRES["Write Reservation\nISO hash\n.xlsx/.xlsb"]
    XLSX_RANGE["Edit Ranges\nISO hash\n.xlsx/.xlsb"]
    VBA_LOCK["VBA Project Lock\nSHA-1 verifier"]
  end
  subgraph nonpw ["⚪ Non-Password"]
    SIG["Digital Signature\nPKI integrity"]
  end

Detection Flowchart¶

How to determine which encryption scheme an Excel file uses:

flowchart TD
  START(["Open Excel file"]) --> EXT{"Extension?"}
  EXT -->|".xls / .xlt"| XLS_CHECK["Read Workbook stream\nFind FilePass record 0x002F"]
  EXT -->|".xlsx / .xlsm / .xlsb"| XLSX_CHECK{"Is it a valid ZIP?"}

  XLSX_CHECK -->|"Yes"| PLAIN["No open encryption\nCheck XML protection elements\nin xl/worksheets/*.xml\nand xl/workbook.xml"]
  XLSX_CHECK -->|"No — it's OLE/CFB"| ENC_INFO["Read \\EncryptionInfo stream\nfrom the CFB container"]

  XLS_CHECK --> HAS_FP{"FilePass\nrecord found?"}
  HAS_FP -->|"No"| XLS_PROT["No open encryption\nCheck Password records:\n0x0013, 0x005B, 0x01BC"]
  HAS_FP -->|"Yes"| FP_TYPE{"wEncryptionType?"}
  FP_TYPE -->|"0x0000"| XOR["🔴 XOR Obfuscation\n4-byte XORObfuscation\nkey + verifier"]
  FP_TYPE -->|"0x0001"| RC4_VER{"EncryptionVersionInfo\nvMajor?"}

  RC4_VER -->|"0x0001"| RC4_MD5["🔴 RC4 + MD5\n40-bit effective key\n52-byte header"]
  RC4_VER -->|"0x0002 / 0x0003 / 0x0004"| RC4_CRYPTO["🔴 RC4 CryptoAPI + SHA-1\nKeySize 40–128 bits"]

  ENC_INFO --> OOXML_VER{"vMinor?"}
  OOXML_VER -->|"0x0002"| STANDARD["🔴 ECMA-376 Standard\nAES-ECB + SHA-1 × 50000"]
  OOXML_VER -->|"0x0004"| AGILE["🔴 ECMA-376 Agile\nXML-negotiated algorithms\n(default SHA-512 + AES-256)"]
  OOXML_VER -->|"0x0003"| EXT_ENC["⚪ Extensible / External\nfExternal flag set"]

Container Structure¶

Where each gate's data physically lives:

flowchart LR
  subgraph xls [".xls — OLE/CFB · Workbook Stream"]
    direction TB
    FP["🔴 FilePass 0x002F\nwEncryptionType (u16)\n0x0000→XORObfuscation: key(u16) · verificationBytes(u16)\n0x0001→EncryptionVersionInfo: vMajor · vMinor\n+ Salt(16B) · EncryptedVerifier(16B) · EncryptedVerifierHash"]
    PW["🟡 Password 0x0013\nwPassword (u16)\nSheet substream → sheet protect\nGlobals substream → workbook protect"]
    FS["🟡 FileSharing 0x005B\nwResPass (u16) · stUNUsername\nWriteProtect 0x0086 must coexist"]
    P4R["🟡 Prot4RevPass 0x01BC\nprotPwdRev (u16)"]
    FEAT["🟡 Feat 0x0868 → FeatProtection\nwPassword (u32, 16-bit zero-extended)\nstTitle · fSD · sdContainer"]
    VBA_S["🟡 VBA Storage → PROJECT stream\nDPB= (password hash or cleartext)\nCMG= (protection state)\nGC= (visibility)"]
    SIG_S["⚪ _signatures stream\nDigSigBlob → PKCS#7 SignedData"]
  end
  subgraph xlsx [".xlsx — OPC/ZIP or CFB wrapper"]
    direction TB
    EI["🔴 \\EncryptionInfo stream\nvMajor · vMinor · Reserved\n+ XML or binary header\n\\EncryptedPackage = encrypted OPC ZIP"]
    FSX["🟡 xl/workbook.xml → fileSharing\nalgorithmName · hashValue\nsaltValue · spinCount\nreservationPassword (legacy u16)"]
    WPX["🟡 xl/workbook.xml → workbookProtection\nworkbookAlgorithmName · workbookHashValue\nworkbookSaltValue · workbookSpinCount\nworkbookPassword (legacy u16)\nrevisionsAlgorithmName · revisionsHashValue\nrevisionsSaltValue · revisionsSpinCount\nlockStructure · lockWindows · lockRevision"]
    SPX["🟡 xl/worksheets/sheetN.xml → sheetProtection\nalgorithmName · hashValue\nsaltValue · spinCount\npassword (legacy u16)\nsheet · objects · scenarios · formatCells\ninsertRows · deleteColumns · sort · autoFilter ..."]
    PRX["🟡 xl/worksheets/sheetN.xml → protectedRange\nalgorithmName · hashValue\nsaltValue · spinCount\npassword (legacy u16)\nname · sqref"]
    VBAX["🟡 xl/vbaProject.bin → PROJECT stream\nDPB= · CMG= · GC="]
    SIGX["⚪ _xmlsignatures/sigN.xml\nXML-DSig Signature + XAdES"]
  end

VelvetSweatshop Default Password¶

Spec-confirmed default password — [MS-OFFCRYPTO] §2.4.2.3

Password: VelvetSweatshop (\x56\x65\x6C\x76\x65\x74\x53\x77\x65\x61\x74\x73\x68\x6F\x70)

Trigger: Excel auto-encrypts the workbook stream under this fixed password when a protection record (Password 0x0013, Prot4RevPass 0x01BC, or their .xlsb equivalents) carries a non-zero verifier but no user open password was set

Always try this first on any encrypted Excel file before password-cracking attempts

Applies to: Excel 2007, Excel 2010, Excel 2013 — per [MS-OFFCRYPTO] Appendix A notes \<24>, \<25>

Gate Quick Reference¶

.xls — legacy binary¶

	Gate	Record / Location	Algorithm	Spec
🔴	Open — XOR	`FilePass` 0x002F, `wEncryptionType`=0x0000	XOR obfuscation Method 1	[MS-OFFCRYPTO] §2.3.7
🔴	Open — RC4+MD5	`FilePass` 0x002F, vMajor=1/vMinor=1	RC4-MD5, 40-bit	[MS-OFFCRYPTO] §2.3.6
🔴	Open — RC4 CryptoAPI	`FilePass` 0x002F, vMajor=2–4/vMinor=2	RC4-CryptoAPI-SHA1	[MS-OFFCRYPTO] §2.3.5
🟡	Write reservation	`FileSharing` 0x005B, `wResPass` u16	16-bit verifier ([MS-OFFCRYPTO] §2.3.7.1)	[MS-XLS] §2.4.118
🟡	Protect sheet	`Password` 0x0013 in sheet substream	16-bit verifier ([MS-OFFCRYPTO] §2.3.7.1)	[MS-XLS] §2.4.191, §2.2.9
🟡	Protect workbook	`Password` 0x0013 in Globals substream	16-bit verifier ([MS-OFFCRYPTO] §2.3.7.1)	[MS-XLS] §2.4.191, §2.4.207
🟡	Edit ranges	`FeatProtection` in `Feat` 0x0868	16-bit verifier, zero-extended to 32 bits	[MS-XLS] §2.4.111, §2.5.124
🟡	Revision protect	`Prot4RevPass` 0x01BC, `protPwdRev` u16	16-bit verifier ([MS-OFFCRYPTO] §2.3.7.1)	[MS-XLS] §2.4.205–206
🟡	Object protect	`ObjProtect` 0x0063	No independent password — uses sheet's `Password`	[MS-XLS] §2.4.183
🟡	Scenario protect	`ScenarioProtect` 0x00DD	No independent password — uses sheet's `Password`	[MS-XLS] §2.4.245
🟡	VBA project lock	VBA storage → `PROJECT` stream `DPB=`	VBA password SHA-1	[MS-OVBA] §2.3.1.16, §2.4.4
⚪	Digital signature	`_signatures` / `_xmlsignatures`	PKI — MD5+RSA or xmldsig/XAdES	[MS-OFFCRYPTO] §2.5

.xlsx / .xlsb — OOXML¶

	Gate	Element / Record	Algorithm	Spec
🔴	Open — Standard	`\EncryptionInfo` vMinor=0x0002	ECMA-376 Standard AES-ECB	[MS-OFFCRYPTO] §2.3.4.5–9
🔴	Open — Agile	`\EncryptionInfo` vMinor=0x0004	ECMA-376 Agile AES-CBC	[MS-OFFCRYPTO] §2.3.4.10–15
🟡	Write reservation	`<fileSharing>` / `BrtFileSharingIso`	ISO hash or 16-bit legacy	[MS-OFFCRYPTO] §2.4.2.4
🟡	Protect sheet	`<sheetProtection>` / `BrtSheetProtectionIso`	ISO hash or 16-bit legacy	[MS-OFFCRYPTO] §2.4.2.4
🟡	Protect workbook	`<workbookProtection>` / `BrtBookProtectionIso`	ISO hash or 16-bit legacy	[MS-OFFCRYPTO] §2.4.2.4
🟡	Edit ranges	`<protectedRange>` / `BrtRangeProtectionIso`	ISO hash or 16-bit legacy	[MS-XLSX] §2.6.56
🟡	Revision protect	`<workbookProtection>` `revisions*` attrs	ISO hash	[MS-OE376] §2.1.621
🟡	VBA project lock	`xl/vbaProject.bin` → `PROJECT` stream	VBA password SHA-1	[MS-OVBA] §2.3.1.16, §2.4.4
⚪	Digital signature	`_xmlsignatures/`	xmldsig/XAdES PKI	[MS-OFFCRYPTO] §2.5.2–3

Specification Detail¶

`.xls` — legacy binary (OLE/CFB, BIFF8) — full gate table¶

Gate	Location in file	Algorithm / mechanism	Spec reference
🔴 Open / encrypt — XOR obfuscation	`FilePass` record (record type 47 / 0x002F) in the `Workbook` stream; `wEncryptionType` = 0x0000 selects `XORObfuscation` sub-structure (4 bytes: key + verifier). Record headers (type + size) and certain records (BOF, FilePass, UsrExcl, FileLock, InterfaceHdr, RRDInfo, RRDHead) are never obfuscated; `lbPlyPos` in BoundSheet8 is also exempt.	XOR obfuscation Method 1: password verifier derivation ([MS-OFFCRYPTO] §2.3.7.1), XOR array init ([MS-OFFCRYPTO] §2.3.7.2), XOR data transformation ([MS-OFFCRYPTO] §2.3.7.3). Password is truncated to 15 single-byte ANSI characters. Produces a 16-bit verifier and a 16-byte XOR array. See xor-obfuscation.	[MS-XLS] §2.4.117, §2.2.10; [MS-OFFCRYPTO] §2.3.7
🔴 Open / encrypt — RC4 + MD5 (40-bit)	`FilePass` record with `wEncryptionType` = 0x0001 and `encryptionInfo` first two bytes = 0x0001, signifying EncryptionVersionInfo (vMajor=1, vMinor=1) → 52-byte RC4 encryption header containing Salt (16 bytes), EncryptedVerifier (16 bytes), EncryptedVerifierHash (16 bytes).	RC4 encryption: key derivation uses MD5 hashing, first 5 bytes of H(password) as TruncatedHash, 336-byte IntermediateBuffer ([MS-OFFCRYPTO] §2.3.6.2). Effective key seed is 40 bits despite 128-bit RC4 key. Verification via MD5 of decrypted verifier. See rc4-md5-legacy.	[MS-XLS] §2.4.117, §2.2.10; [MS-OFFCRYPTO] §2.3.6
🔴 Open / encrypt — RC4 CryptoAPI + SHA-1	`FilePass` record with `wEncryptionType` = 0x0001 and `encryptionInfo` first two bytes in {0x0002, 0x0003, 0x0004} → RC4 CryptoAPI encryption header ([MS-OFFCRYPTO] §2.3.5.1): EncryptionVersionInfo, EncryptionHeader (AlgID=0x6801 for RC4, AlgIDHash=0x8004 for SHA-1, KeySize 40–128 bits), EncryptionVerifier.	RC4 CryptoAPI: key derivation is H0 = SHA-1(salt + password), Hfinal = SHA-1(H0 + blockNumber), no iteration ([MS-OFFCRYPTO] §2.3.5.2). Verification via SHA-1 of decrypted verifier. When RC4 CryptoAPI is used, certain streams are stored in the Encryption Stream ([MS-XLS] §2.1.7.6) per [MS-OFFCRYPTO] §2.3.5.4. See rc4-cryptoapi-sha1.	[MS-XLS] §2.4.117, §2.2.10; [MS-OFFCRYPTO] §2.3.5
🟡 Modify / write-reservation	`FileSharing` record (record type 91 / 0x005B) in the Globals substream. `wResPass` (unsigned 16-bit) at data offset +2 holds the password verifier; a value of 0 means no write-reservation password. `stUNUsername` names the user who set the reservation. The `WriteProtect` record (record type 134 / 0x0086) MUST also exist when write protection is active.	16-bit password verifier via CreatePasswordVerifier_Method1 ([MS-OFFCRYPTO] §2.3.7.1). When a write-reservation is set but no user-supplied open password exists, the workbook can be encrypted under the default password (see VelvetSweatshop below). See xor-obfuscation.	[MS-XLS] §2.4.118, §2.4.350; [MS-OFFCRYPTO] §2.4.2.2, §2.3.7.1
🟡 Protect sheet	`Password` record (record type 19 / 0x0013) in the worksheet, chart sheet, macro sheet, or dialog sheet substream. `wPassword` (unsigned 16-bit) holds the verifier. This record MUST exist if and only if the sheet is protected. The `Protect` record (record type 18 / 0x0012) in the same substream specifies the protection state (`fLock` = 0x0001 = protected).	16-bit password verifier via CreatePasswordVerifier_Method1 ([MS-OFFCRYPTO] §2.3.7.1). This is the Password Verifier Algorithm described in [MS-XLS] §2.2.9: Unicode password → ANSI code-page conversion → Method 1 derivation. See xor-obfuscation.	[MS-XLS] §2.4.191, §2.4.207, §2.2.9; [MS-OFFCRYPTO] §2.3.7.1
🟡 Protect workbook (structure / windows)	`Password` record (record type 0x0013) in the Globals substream. `wPassword` = 0x0000 means no password. Separately, the `Protect` record in Globals sets `fLock` and the `WinProtect` record (record type 0x0019) controls whether workbook windows can be resized or moved.	Same 16-bit Password Verifier Algorithm as sheet protection ([MS-XLS] §2.2.9).	[MS-XLS] §2.4.191, §2.4.207, §2.4.347
🟡 Allow-edit-ranges	`Feat` record (record type 2152 / 0x0868) with a `FeatProtection` structure ([MS-XLS] §2.5.124) containing `wPassword` (unsigned 32-bit verifier), `stTitle`, and optional `sdContainer` (Windows security descriptor identifying users who can edit without a password). Linked to cell ranges via the Feat record's `refs` field.	Password verifier is the same Password Verifier Algorithm ([MS-XLS] §2.2.9); the `wPassword` field stores the 16-bit result zero-extended to 32 bits. When `fSD` = 1, the `sdContainer` carries a self-relative security descriptor for ACL-based authorization (users listed in the descriptor can edit without entering a password).	[MS-XLS] §2.4.111, §2.5.124, §2.2.9
🟡 Shared-workbook revision protection	`Prot4Rev` record (record type 0x01AF) with `fRevLock` Boolean (0x0001 = removal of revision logs disallowed). Followed by `Prot4RevPass` record (record type 0x01BC) whose `protPwdRev` (unsigned 16-bit) is the verifier required to change `fRevLock`.	16-bit Password Verifier Algorithm ([MS-XLS] §2.2.9, [MS-OFFCRYPTO] §2.3.7.1).	[MS-XLS] §2.4.205, §2.4.206
🟡 Object protection	`ObjProtect` record (record type 99 / 0x0063) in the sheet substream. `fLockObj` = 0x0001 means objects are protected. This record exists if and only if the sheet is protected and the objects on the sheet are protected.	No independent password — object protection is governed by the sheet's `Password` record (same 16-bit verifier).	[MS-XLS] §2.4.183
🟡 Scenario protection	`ScenarioProtect` record (record type 0x00DD) in the sheet substream. `fScenProtect` = 0x0001 means scenarios are protected.	No independent password — scenario protection is governed by the sheet's `Password` record.	[MS-XLS] §2.4.245
🟡 VBA project lock	Embedded VBA storage (`_VBA_PROJECT_CUR` or `VBA`) → `PROJECT` stream. `ProjectProtectionState` (CMG= line, [MS-OVBA] §2.3.1.15) controls whether the project is "locked for viewing". `ProjectPassword` (DPB= line, [MS-OVBA] §2.3.1.16) stores either a password hash (29-byte Hash Data Structure) or a plaintext password, obfuscated by the Data Encryption algorithm ([MS-OVBA] §2.4.3). When password is a hash, `ProjectId.ProjectCLSID` MUST be `{00000000-0000-0000-0000-000000000000}`.	DPB obfuscation ([MS-OVBA] §2.4.3): three seed bytes + XOR-based encryption. The actual password hash uses SHA-1 via the Hash Data Structure ([MS-OVBA] §2.4.4). See vba-project-password.	[MS-OVBA] §2.3.1.15, §2.3.1.16, §2.4.3, §2.4.4
⚪ Digital signature	`_signatures` stream in root storage (CryptoAPI format, MD5 hash, [MS-OFFCRYPTO] §2.5.1) or `_xmlsignatures` storage (xmldsig/XAdES format, [MS-OFFCRYPTO] §2.5.2–2.5.3). For CryptoAPI sigs, the hash is generated by recursively traversing OLE streams/storages excluding `\0x06DataSpaces`, `_signatures`, and `\0x09DRMContent`; for the Workbook stream, application-specific filtering is applied ([MS-XLS] §2.1.7.15).	CryptoAPI digital signature: MD5 hash of stream data + RSA signing ([MS-OFFCRYPTO] §2.5.1.5). Xmldsig: XML-Signature Syntax and Processing [XMLDSig] with optional XAdES extensions ([MS-OFFCRYPTO] §2.5.2.6).	[MS-OFFCRYPTO] §2.5.1, §2.5.2, §2.5.3

`.xlsx` / `.xlsb` — OOXML (OPC/ZIP, Excel 2007+) — full gate table¶

.xlsb carries the identical gates but as binary Brt* records instead of XML elements — noted per row where applicable.

Gate	Location in file	Algorithm / mechanism	Spec reference
🔴 Open / encrypt — ECMA-376 standard	OLE/CFB wrapper: `\EncryptionInfo` stream (EncryptionVersionInfo vMajor in {0x0002,0x0003,0x0004}, vMinor=0x0002), `\EncryptedPackage` stream. EncryptionHeader: fCryptoAPI=1, fAES=1, AlgID in {0x660E, 0x660F, 0x6610} (AES-128/192/256), AlgIDHash=0x8004 (SHA-1). The entire OPC ZIP is encrypted as a single stream inside `\EncryptedPackage`. Data spaces structures under `\0x06DataSpaces` associate the package with the StrongEncryptionTransform.	Key derivation: H0 = SHA-1(salt + password), then 50,000 iterations Hn = SHA-1(iterator + Hn-1), then Hfinal = SHA-1(Hn + blockKey), followed by HMAC-like X1/X2 derivation to reach cbRequiredKeyLength bits ([MS-OFFCRYPTO] §2.3.4.7). Encryption uses AES-ECB. Verification via SHA-1 of decrypted verifier ([MS-OFFCRYPTO] §2.3.4.9). See ecma376-standard.	[MS-OFFCRYPTO] §2.3.4.5, §2.3.4.7–§2.3.4.9, §2.3.4.4
🔴 Open / encrypt — ECMA-376 agile	OLE/CFB wrapper: `\EncryptionInfo` stream (vMajor=0x0004, vMinor=0x0004, Reserved=0x00000040), followed by XML descriptor. `\EncryptedPackage` encrypted in 4096-byte segments. XML descriptor carries `<keyData>` (cipherAlgorithm, hashAlgorithm, keyBits, saltValue, blockSize), `<dataIntegrity>` (HMAC for corruption detection), and `<keyEncryptors>` with one `<p:encryptedKey>` per PasswordKeyEncryptor (spinCount, saltValue, encryptedVerifierHashInput, encryptedVerifierHashValue, encryptedKeyValue).	Key derivation: H0 = H(salt + password), iterated spinCount times ([MS-OFFCRYPTO] §2.3.4.11); Hfinal = H(Hn + blockKey). IV generation per §2.3.4.12 using KeySalt + blockKey. Cipher algorithm and hash algorithm specified in XML (typically AES-256-CBC + SHA-512 for modern files; defaults are AES-128-CBC + SHA-1). DataIntegrity HMAC validates the entire EncryptedPackage including StreamSize. CertificateKeyEncryptor allows public-key-based decryption alongside password. See ecma376-agile.	[MS-OFFCRYPTO] §2.3.4.10–§2.3.4.15
🟡 Modify / write-reservation	`<fileSharing>` element in `xl/workbook.xml` ([ISO/IEC 29500-1] §3.2.12). Attributes: `reservationPassword` (legacy 16-bit hash) or `algorithmName`/`hashValue`/`saltValue`/`spinCount` (ISO hash). `userName` names the reserving user (max 54 chars). `.xlsb`: `BrtFileSharing` / `BrtFileSharingIso` record.	Legacy: 16-bit verifier identical to [MS-OFFCRYPTO] §2.3.7.1. ISO: iterated hash per [MS-OFFCRYPTO] §2.4.2.4 — H0 = H(salt + password), then Hn = H(Hn-1 + iterator) for spinCount iterations. algorithmName selects the hash function (SHA-1 through SHA-512, WHIRLPOOL, etc.). See iso-protection-hash.	[MS-XLSX] / [ISO/IEC 29500-1] §3.2.12; [MS-OE376] §2.1.607; [MS-OFFCRYPTO] §2.4.2.4
🟡 Protect sheet	`<sheetProtection>` element in `xl/worksheets/sheetN.xml` ([ISO/IEC 29500-1] §3.3.1.81). Boolean attributes control which actions remain permitted: `sheet`, `objects`, `scenarios`, `formatCells`, `formatColumns`, `formatRows`, `insertColumns`, `insertRows`, `insertHyperlinks`, `deleteColumns`, `deleteRows`, `selectLockedCells`, `sort`, `autoFilter`, `pivotTables`, `selectUnlockedCells`. Password stored via `password` (legacy 16-bit) or `algorithmName`/`hashValue`/`saltValue`/`spinCount` (ISO hash). Chart sheet: `<sheetProtection>` in `xl/chartsheets/` ([ISO/IEC 29500-1] §3.3.1.82). `.xlsb`: `BrtSheetProtection` / `BrtSheetProtectionIso`, `BrtCsProtection` / `BrtCsProtectionIso`.	ISO hash per [MS-OFFCRYPTO] §2.4.2.4 (or legacy 16-bit when only `password` attribute present). For dialog sheets, Office requires that `objects` and `scenarios` both be true when protected, with `sheet` always true ([MS-OE376] §2.1.681). See iso-protection-hash.	[MS-XLSX] / [ISO/IEC 29500-1] §3.3.1.81–82; [MS-OE376] §2.1.681–682; [MS-OFFCRYPTO] §2.4.2.4
🟡 Protect workbook (structure / windows)	`<workbookProtection>` element in `xl/workbook.xml` ([ISO/IEC 29500-1] §3.2.29). `lockStructure` prevents adding/deleting/renaming sheets. `lockWindows` prevents resizing/moving workbook windows (note: if all sheets have `windowProtection=false`, `lockWindows` is also saved as false per [MS-OE376] §2.1.621). `workbookPassword` (legacy 16-bit) or `workbookAlgorithmName`/`workbookHashValue`/`workbookSaltValue`/`workbookSpinCount` (ISO hash). `lockRevision` controls whether change history in a shared workbook can be removed, with `revisionsPassword` / `revisionsAlgorithmName` / `revisionsHashValue` / `revisionsSaltValue` / `revisionsSpinCount` as the corresponding verifier. `.xlsb`: `BrtBookProtection` / `BrtBookProtectionIso`.	ISO hash per [MS-OFFCRYPTO] §2.4.2.4. Note: Office uses `workbookPassword` for unlocking structure/windows (not revisions, despite what the standard's attribute name might suggest) — per [MS-OE376] §2.1.621(d). See iso-protection-hash.	[MS-XLSX] / [ISO/IEC 29500-1] §3.2.29; [MS-OE376] §2.1.621; [MS-OFFCRYPTO] §2.4.2.4
🟡 Allow-edit-ranges	`<protectedRange>` elements inside `<protectedRanges>` in `xl/worksheets/sheetN.xml` ([ISO/IEC 29500-1] §3.3.1.69). Each range has `name` (unique within the sheet, starting with a letter), `sqref` (cell references), and password via `password` (legacy 16-bit) or `algorithmName`/`hashValue`/`saltValue`/`spinCount` (ISO hash). `.xlsb`: `BrtRangeProtection` / `BrtRangeProtectionIso`.	ISO hash per [MS-OFFCRYPTO] §2.4.2.4.	[MS-XLSX] / [ISO/IEC 29500-1] §3.3.1.69; [MS-OE376] §2.1.672; [MS-OFFCRYPTO] §2.4.2.4
🟡 Shared-workbook revision protection	`<workbookProtection>` element's `revisionsHashValue`/`revisionsAlgorithmName`/`revisionsSaltValue`/`revisionsSpinCount` attributes in `xl/workbook.xml`. `lockRevision` = true disallows removal of revision logs.	ISO hash per [MS-OFFCRYPTO] §2.4.2.4. Per [MS-OE376] §2.1.621(c), Office uses `lockRevision` to mean "change history in a shared workbook cannot be removed".	[MS-XLSX] / [ISO/IEC 29500-1] §3.2.29; [MS-OE376] §2.1.621
🟡 VBA project lock	`xl/vbaProject.bin` (an embedded OLE/CFB binary part) → `PROJECT` stream. Same `CMG`/`DPB`/`GC` protection state and `ProjectPassword` structure as the `.xls` case.	Same DPB obfuscation and SHA-1 hash as the binary format ([MS-OVBA] §2.3.1.15–16, §2.4.3–4). See vba-project-password.	[MS-OVBA] §2.3.1.15, §2.3.1.16, §2.4.3, §2.4.4
⚪ Digital signature	`_xmlsignatures/` storage within the OPC package, containing XML-Signature streams per [MS-OFFCRYPTO] §2.5.2–2.5.3 and [ECMA-376] Part 2 §12. Each signature stream is a valid xmldsig `<Signature>` with optional XAdES extensions.	XML-Signature Syntax and Processing [XMLDSig]; Manifest covers all package streams except `_xmlsignatures`, `\0x06DataSpaces`, `MsoDataStore`, etc. ([MS-OFFCRYPTO] §2.5.2.4). Optional XAdES-EPES through XAdES-X-L extensions ([MS-OFFCRYPTO] §2.5.2.6).	[MS-OFFCRYPTO] §2.5.2, §2.5.3

Extraction Targets by Gate¶

What Python code needs to extract for each gate — field names, types, locations, and "gate is active" indicators.

🔴 Open / Encrypt — .xls binary¶

Location: Workbook stream (or Book), FilePass record (rt = 0x002F)
Gate active when: FilePass record exists
Extract:
wEncryptionType — u16 LE at body offset 0 → 0x0000 = XOR, 0x0001 = RC4
If XOR (0x0000): XORObfuscation (4 bytes) → key (u16 LE), verificationBytes (u16 LE)
If RC4 (0x0001): read EncryptionVersionInfo → vMajor (u16 LE), vMinor (u16 LE)
- vMajor=1, vMinor=1 → RC4+MD5: Salt (16B at offset 0x04), EncryptedVerifier (16B at 0x14), EncryptedVerifierHash (16B at 0x24)
- vMajor=2–4, vMinor=2 → RC4 CryptoAPI: parse EncryptionHeader (AlgID, AlgIDHash, KeySize) + EncryptionVerifier (SaltSize, Salt 16B, EncryptedVerifier 16B, VerifierHashSize, EncryptedVerifierHash 20B)

🔴 Open / Encrypt — .xlsx/.xlsb OOXML¶

Location: \EncryptionInfo stream in the OLE/CFB wrapper (file is NOT a ZIP when encrypted)
Gate active when: file fails ZIP magic check (not PK\x03\x04) and has OLE/CFB signature (D0 CF 11 E0)
Extract:
Bytes 0–7: vMajor (u16 LE), vMinor (u16 LE), Reserved (u32 LE)
If vMinor=0x0002 (Standard): parse EncryptionHeader + EncryptionVerifier per [MS-OFFCRYPTO] §2.3.4.5
If vMinor=0x0004 (Agile): parse UTF-8 XML from byte 8 onward → extract from <p:encryptedKey>: spinCount, saltSize, blockSize, keyBits, hashSize, cipherAlgorithm, cipherChaining, hashAlgorithm, saltValue (base64), encryptedVerifierHashInput (base64), encryptedVerifierHashValue (base64), encryptedKeyValue (base64)

🟡 Sheet Protection — .xls binary¶

Location: Password record (rt = 0x0013) in the worksheet/chart/macro/dialog substream
Gate active when: Protect record (rt = 0x0012) has fLock = 0x0001 AND Password record exists with wPassword ≠ 0x0000
Extract: wPassword — u16 LE (the 16-bit verifier)

🟡 Sheet Protection — .xlsx OOXML¶

Location: xl/worksheets/sheetN.xml, element <sheetProtection>
Gate active when: sheet="1" attribute is present (or any of the boolean protection attributes)
Extract (ISO): algorithmName (string), hashValue (base64), saltValue (base64), spinCount (decimal)
Extract (legacy): password (4-hex-digit ST_UnsignedShortHex, e.g. "CC40")
Also extract: boolean flags: sheet, objects, scenarios, formatCells, formatColumns, formatRows, insertColumns, insertRows, insertHyperlinks, deleteColumns, deleteRows, selectLockedCells, sort, autoFilter, pivotTables, selectUnlockedCells

🟡 Workbook Protection — .xls binary¶

Location: Password record (rt = 0x0013) in the Globals substream
Gate active when: Protect record in Globals has fLock = 0x0001
Extract: wPassword — u16 LE

🟡 Workbook Protection — .xlsx OOXML¶

Location: xl/workbook.xml, element <workbookProtection>
Gate active when: lockStructure="1" or lockWindows="1" is present
Extract (ISO, structure): workbookAlgorithmName, workbookHashValue (base64), workbookSaltValue (base64), workbookSpinCount
Extract (ISO, revisions): revisionsAlgorithmName, revisionsHashValue (base64), revisionsSaltValue (base64), revisionsSpinCount
Extract (legacy): workbookPassword (4-hex), revisionsPassword (4-hex)
Also extract: lockStructure, lockWindows, lockRevision (booleans)

🟡 Write Reservation — .xls binary¶

Location: FileSharing record (rt = 0x005B) in the Globals substream
Gate active when: WriteProtect record (rt = 0x0086) exists AND wResPass ≠ 0x0000
Extract: wResPass — u16 LE at data offset +2; stUNUsername — XLUnicodeString

🟡 Write Reservation — .xlsx OOXML¶

Location: xl/workbook.xml, element <fileSharing>
Gate active when: <fileSharing> element exists with any password attribute
Extract (ISO): algorithmName, hashValue (base64), saltValue (base64), spinCount
Extract (legacy): reservationPassword (4-hex)
Also extract: userName (string, max 54 chars)

🟡 Edit Ranges — .xls binary¶

Location: Feat record (rt = 0x0868) with FeatProtection structure
Gate active when: wPassword ≠ 0x00000000
Extract: wPassword — u32 LE (16-bit verifier zero-extended); stTitle — range name; fSD — boolean; sdContainer — security descriptor (if fSD=1)

🟡 Edit Ranges — .xlsx OOXML¶

Location: xl/worksheets/sheetN.xml, element <protectedRange> inside <protectedRanges>
Gate active when: <protectedRange> element exists with any password attribute
Extract (ISO): algorithmName, hashValue (base64), saltValue (base64), spinCount
Extract (legacy): password (4-hex)
Also extract: name (string, unique per sheet), sqref (cell reference string)

🟡 Revision Protection — .xls binary¶

Location: Prot4RevPass record (rt = 0x01BC)
Gate active when: Prot4Rev record (rt = 0x01AF) has fRevLock = 0x0001 AND protPwdRev ≠ 0x0000
Extract: protPwdRev — u16 LE

🟡 VBA Project Lock¶

Location (binary): VBA storage → PROJECT stream (INI-style text)
Location (OOXML): xl/vbaProject.bin (embedded OLE/CFB) → PROJECT stream
Gate active when: DPB= line exists with length > the no-password sentinel
Extract: ID= line (CLSID GUID for ProjKey derivation); DPB= hex string (decode with §2.4.3); CMG= hex string (protection state); GC= hex string (visibility)

⚪ Digital Signature¶

Location (binary): _signatures stream or _xmlsignatures storage
Location (OOXML): _xmlsignatures/sigN.xml parts
Gate active when: the stream/storage/part exists
Extract: PKCS#7 SignedData blob (binary) or XML-DSig <Signature> elements (OOXML)

Detailed Notes¶

VelvetSweatshop default password¶

The spec explicitly defines a fixed default encryption password used when a workbook has protection records but no user-supplied open password. [MS-OFFCRYPTO] §2.4.2.3 / Appendix A note <24> states that documents generated by Excel 2007, Excel 2010, and Excel 2013 "can be encrypted as specified in section 2.3 with the following password: \x56\x65\x6C\x76\x65\x74\x53\x77\x65\x61\x74\x73\x68\x6F\x70" — which decodes to the ASCII string VelvetSweatshop. Appendix A note <25> repeats the same for write-protected documents under [MS-OFFCRYPTO] §2.4.2.2. [MS-XLS] §2.2.10 and [MS-XLSB] §2.2.11 cross-reference these conditions. The trigger is: the Password record (0x0013, sheet or workbook), Prot4RevPass (0x01BC), or their .xlsb equivalents (BrtBookProtection, BrtBookProtectionIso) carry a non-zero verifier, but no user open password was set, so the workbook stream is auto-encrypted under this fixed password.

Password Verifier Algorithm (16-bit, BIFF8)¶

[MS-XLS] §2.2.9 describes the Password Verifier Algorithm used by the Password, FileSharing, Prot4RevPass, FeatProtection, and FilePass records. The spec states: "This password verifier is used to prevent accidental editing, and is not designed to be used as a security feature." The derivation is a two-stage process: (1) the Unicode password string is converted to a single-byte ANSI string using the code-page conversion algorithm specified in the revisionsPassword attribute in [ECMA-376] Part 4 §3.2.29; (2) this ANSI string is fed into the XOR obfuscation password verifier derivation method 1 ([MS-OFFCRYPTO] §2.3.7.1), which produces a 16-bit value. Passwords are truncated to 15 characters ([MS-OFFCRYPTO] §4.1.3.4). Multiple passwords can map to the same 16-bit verifier.

ISO Write Protection Method (OOXML)¶

[MS-OFFCRYPTO] §2.4.2.4 specifies the ISO password hashing algorithm used by all OOXML protection elements (sheetProtection, workbookProtection, protectedRange, fileSharing). The algorithm takes: Password (1–255 Unicode characters), AlgorithmName (SHA-1, SHA-256, SHA-384, SHA-512, MD5, MD4, MD2, RIPEMD-128, RIPEMD-160, WHIRLPOOL, or others supported by the OS), Salt (random, up to 65,536 bytes), and SpinCount (0 to 10,000,000). Derivation: H0 = H(salt + password), then Hn = H(Hn-1 + iterator) iterated SpinCount times. The final hash is stored as base64 in hashValue, the salt as base64 in saltValue. [MS-OE376] §2.1.607, §2.1.621, §2.1.672, §2.1.681 all document that Office uses this ISO verifier when the UseIsoPasswordVerifier registry key is set to 1 (HKCU/Software/Microsoft/Office//Common/Security/UseIsoPasswordVerifier).

Legacy vs. ISO protection attribute coexistence¶

The OOXML protection elements support both a legacy password attribute (16-bit hash from CreatePasswordVerifier_Method1) and the ISO algorithmName/hashValue/saltValue/spinCount attribute set. [MS-OE376] §2.1.681 specifies that when hashValue is omitted, the password attribute contains the hash for the workbook. When both are present, the ISO hash takes precedence. For <fileSharing>, [MS-OE376] §2.1.607 states the same dual-attribute model with reservationPassword as the legacy fallback.

Encryption method selection in .xls¶

[MS-XLS] §2.2.10 states that when a .xls file is saved with encryption, it MUST use one of: XOR obfuscation ([MS-OFFCRYPTO] §2.3.7), RC4 encryption ([MS-OFFCRYPTO] §2.3.6), or RC4 CryptoAPI encryption ([MS-OFFCRYPTO] §2.3.5). The FilePass record's wEncryptionType field (0x0000 = XOR, 0x0001 = RC4) and, for RC4, the EncryptionVersionInfo vMajor value (0x0001 = RC4+MD5; 0x0002/0x0003/0x0004 = RC4 CryptoAPI) jointly determine the scheme. [MS-XLS] §2.2.10 also documents which streams are encrypted: the Workbook stream, Pivot Cache Storage, and Revision Stream are always encrypted; VBA storage, OLE stream, Office Toolbars, and signature-related streams are never encrypted. For RC4 CryptoAPI, additional streams are encrypted inside the Encryption Stream per [MS-OFFCRYPTO] §2.3.5.4.

BIFF8 record-level encryption constraints¶

[MS-XLS] §2.2.10 specifies that when obfuscating/encrypting BIFF records, "the record type and record size components MUST NOT be obfuscated or encrypted". Additionally, the following records MUST NOT be encrypted: BOF, FilePass, UsrExcl, FileLock, InterfaceHdr, RRDInfo, RRDHead. The lbPlyPos field of BoundSheet8 is also exempt. For RC4 and RC4 CryptoAPI, record data is encrypted in 1024-byte blocks; the block number resets to zero at the beginning of every BIFF record stream and increments at each 1024-byte boundary.

Protection sub-gates and their scope¶

Several protection sub-gates in .xls all depend on the same 16-bit Password Verifier Algorithm and are subordinate to sheet protection: ObjProtect ([MS-XLS] §2.4.183) protects objects on a sheet (exists if and only if the sheet is protected and objects are protected, fLockObj MUST be 0x0001); ScenarioProtect ([MS-XLS] §2.4.245) protects scenarios (fScenProtect = 0x0001); dialog sheet protection is a subset of sheet protection. None of these carry an independent password — they are governed by the sheet's Password record.

Security considerations from the specs¶

XOR obfuscation — [MS-OFFCRYPTO] §4.1.3.4: "XOR obfuscation is not recommended. Document data can easily be extracted. The document password could be retrievable. Passwords are truncated to 15 characters. It is possible for multiple passwords to map to the same key."
RC4 encryption (40-bit) — [MS-OFFCRYPTO] §4.1.3.3: "considered easily reversible and therefore is not recommended when storing sensitive materials." No iteration, no initial RC4 discard, no corruption detection, 40-bit effective key seed, key-stream reuse potential.
RC4 CryptoAPI encryption — [MS-OFFCRYPTO] §4.1.3.2: "considered insecure, and therefore is not recommended when storing sensitive materials." No iteration, no initial discard, no corruption detection, small key lengths possible (40-bit minimum), key-stream reuse.
ECMA-376 standard encryption — [MS-OFFCRYPTO] §4.1.3.1: "does not support CBC and does not have a provision for detecting corruption." AES-ECB mode.
ECMA-376 agile encryption — [MS-OFFCRYPTO] §4.1.3.1: "required to use CBC and corruption detection, and are not subject to the issues noted for standard encryption." SHA-2 recommended; MD2/MD4/MD5/DES not recommended. Passwords limited to 255 Unicode code points.
Document write protection — [MS-OFFCRYPTO] §4.1.4: "Document write protection is not considered to be a security mechanism, and the write protection can easily be removed by using a binary editor."

VBA project password¶

[MS-OVBA] §2.3.1.16 specifies that a VBA project without a password MUST use 0x00 for the Data parameter with Length = 1 in the DPB encryption. A project with a password SHOULD specify a password hash (29-byte Hash Data Structure per [MS-OVBA] §2.4.4.1) or MAY specify the plaintext password, both obfuscated by the Data Encryption algorithm ([MS-OVBA] §2.4.3). When the password hash form is used, ProjectId.ProjectCLSID MUST be {00000000-0000-0000-0000-000000000000} ([MS-OVBA] §2.3.1.16). The ProjectVisibilityState (GC= line, [MS-OVBA] §2.3.1.17) independently controls whether the project is visible (0xFF) or hidden (0x00); when hidden, ProjectProtectionState.fVBEProtected MUST be TRUE.

BIFF Record Framing (.xls)¶

Every record in a BIFF8 stream is a variable-length sequence of bytes with three components [MS-XLS] §2.1.4:

Component	Size	Type	Description
Record type (`rt`)	2 bytes	u16 LE	Identifies the record type per the Record Enumeration [MS-XLS] §2.3
Record size (`cb`)	2 bytes	u16 LE	Byte count of the record data that follows; MUST be >= 0 and <= 8224
Record data	0..8224 bytes	type-specific	Fields specific to the record type

Maximum record data size is 8224 bytes [MS-XLS] §2.1.4. If a record's logical data exceeds 8224 bytes, the first 8224 bytes are stored in the record's data component and the remainder is split into 8224-byte blocks carried by Continue (0x003C), ContinueFrt (0x0812), ContinueFrt11 (0x0875), or ContinueFrt12 (0x087F) records.
The 4-byte header (record type + record size) is never encrypted or obfuscated, even in encrypted streams [MS-XLS] §2.2.10. This means the sequence and sizes of all records can be read without decryption.
Records exempt from encryption/obfuscation [MS-XLS] §2.2.10: BOF (0x0809), FilePass (0x002F), UsrExcl, FileLock, InterfaceHdr, RRDInfo, RRDHead. Additionally, the lbPlyPos field of BoundSheet8 (0x0085) is exempt (the rest of BoundSheet8 IS encrypted).
Block numbering for RC4/CryptoAPI encryption [MS-XLS] §2.2.10: record data is encrypted in 1024-byte blocks. The block number starts at zero at the beginning of every BIFF record stream and increments by one at each 1024-byte boundary. For unencrypted records and record headers, a buffer of all zeros of the same size is passed into RC4 (the output is discarded) to maintain cipher state synchronization.
Workbook stream naming [MS-XLS] §2.1.7.20: the stream MUST be named "Workbook". The name "Book" was used in BIFF5/BIFF7; BIFF8 mandates "Workbook". Some older implementations and third-party tools may write "Book" as a fallback, but the spec requires "Workbook". A file MUST contain exactly one Workbook Stream, which consists of exactly one Globals Substream (first) followed by one or more sheet substreams (Chart Sheet, Dialog Sheet, Macro Sheet, or Worksheet).

FilePass Record Layout (.xls)¶

Record type: 47 (0x002F) [MS-XLS] §2.4.117

The FilePass record specifies the encryption algorithm and provides the password verification structure. If this record exists, the workbook MUST be encrypted.

Offset	Size	Field	Type	Description
data+0	2	`wEncryptionType`	u16 LE	0x0000 = XOR obfuscation; 0x0001 = RC4 encryption
data+2	variable	`encryptionInfo`	variable	Encryption parameters; structure depends on `wEncryptionType`

When wEncryptionType = 0x0000 (XOR obfuscation): encryptionInfo is an XORObfuscation structure [MS-XLS] §2.5.343:

Offset	Size	Field	Type	Description
data+2	2	`key`	u16 LE	XOR obfuscation key; see [MS-OFFCRYPTO] §2.3.6.2 for derivation
data+4	2	`verificationBytes`	u16 LE	Password verification identifier; compared against the Password Verifier Algorithm output

Total record data for XOR: 6 bytes (wEncryptionType + key + verificationBytes).

When wEncryptionType = 0x0001 (RC4 encryption): encryptionInfo starts with EncryptionVersionInfo [MS-OFFCRYPTO] §2.3.4.5:

Offset	Size	Field	Type	Description
data+2	2	`vMajor`	u16 LE	Major version of encryption method
data+4	2	`vMinor`	u16 LE	Minor version of encryption method

The vMajor value selects the encryption sub-type:

`vMajor`	`vMinor`	Encryption scheme	Subsequent structure
0x0001	0x0001	RC4 + MD5 (40-bit effective key)	RC4 encryption header [MS-OFFCRYPTO] §2.3.6.1: Salt (16 bytes), EncryptedVerifier (16 bytes), EncryptedVerifierHash (16 bytes) = 52 bytes total
0x0002, 0x0003, or 0x0004	0x0002	RC4 CryptoAPI + SHA-1	RC4 CryptoAPI encryption header [MS-OFFCRYPTO] §2.3.5.1: EncryptionHeader (AlgID, AlgIDHash, KeySize 40-128 bits) + EncryptionVerifier (SaltSize, Salt 16B, EncryptedVerifier 16B, VerifierHashSize, EncryptedVerifierHash 20B)

Product behavior [MS-XLS] §2.2.10 notes: - Only Excel 2002 and Office Excel 2003 save files with XOR obfuscation. - Only Excel 2002, Office Excel 2003, Office Excel 2007, and Excel 2010 load/save RC4 CryptoAPI. - Excel 97 through Excel 2003: max password length is 15 characters. Office Excel 2007 and Excel 2010: max 255 characters.

Password Record Layout (.xls)¶

Record type: 19 (0x0013) [MS-XLS] §2.4.191

Offset	Size	Field	Type	Description
data+0	2	`wPassword`	u16 LE	16-bit password verifier. 0x0000 = no password. Derived via the Password Verifier Algorithm [MS-XLS] §2.2.9.

In a sheet substream (worksheet, chart sheet, macro sheet, or dialog sheet): the record protects that individual sheet. The record MUST exist if and only if the sheet is protected, and wPassword MUST NOT be 0x0000 [MS-XLS] §2.4.191.
In the Globals substream: the record protects the workbook structure. This record MUST exist in the Globals substream. wPassword = 0x0000 means no workbook password [MS-XLS] §2.4.191.
VelvetSweatshop trigger [MS-XLS] §2.4.191, product note <100>: when wPassword in the Globals substream is not 0x0000, Excel 97 through Excel 2010 encrypt the entire document. If no user-supplied encryption password is set, the default password "VelvetSweatshop" is used.

FileSharing Record Layout (.xls)¶

Record type: 91 (0x005B) [MS-XLS] §2.4.118

Offset	Size	Field	Type	Description
data+0	2	`fReadOnlyRec`	u16 LE (Boolean)	0x0001 = read-only recommended is selected; 0x0000 = not selected
data+2	2	`wResPass`	u16 LE	Write-reservation password verifier. 0x0000 = no write password. Derived via the Password Verifier Algorithm [MS-XLS] §2.2.9.
data+4	2	`iNoResPass`	u16 LE	Present if and only if `wResPass` = 0x0000. MUST be 0x0000.
data+4	variable	`stUNUsername`	XLUnicodeString	Present if and only if `wResPass` != 0x0000. Name of the user who set the write-reservation password. `cch` MUST be <= 54.

Note: iNoResPass and stUNUsername occupy the same offset but are mutually exclusive depending on wResPass. The WriteProtect record (0x0086) MUST also exist when file-level write protection is active; WriteProtect has no data fields — its mere existence is the signal [MS-XLS] §2.4.350.

Prot4RevPass Record Layout (.xls)¶

Record type: 444 (0x01BC) [MS-XLS] §2.4.206

Offset	Size	Field	Type	Description
data+0	2	`protPwdRev`	u16 LE	Password verifier required to change `Prot4Rev.fRevLock`. 0x0000 = no password. Derived via the Password Verifier Algorithm [MS-XLS] §2.2.9.

MUST be 0x0000 if the preceding Prot4Rev record (0x01AF) has fRevLock = 0x0000.
VelvetSweatshop trigger [MS-XLS] §2.4.206, product note <104>: when protPwdRev != 0x0000, the same default encryption behavior applies — the document is encrypted with "VelvetSweatshop" when no explicit encryption password is set.

Protect / WinProtect / ObjProtect / ScenarioProtect Records¶

All four records use the same simple layout: a single 2-byte Boolean field.

Protect — record type 18 (0x0012) [MS-XLS] §2.4.207:

Offset	Size	Field	Type	Description
data+0	2	`fLock`	u16 LE (Boolean)	0x0000 = not protected; 0x0001 = protected

In the Globals substream: specifies workbook protection state. This record MUST exist.
In a sheet substream: the sheet is protected if and only if this record exists; fLock MUST be 0x0001 when present.

WinProtect — record type 25 (0x0019) [MS-XLS] §2.4.347:

Offset	Size	Field	Type	Description
data+0	2	`fLockWn`	u16 LE (Boolean)	0x0000 = workbook windows can be resized/moved and window state can be changed; 0x0001 = windows cannot be resized/moved and window state cannot be changed

ObjProtect — record type 99 (0x0063) [MS-XLS] §2.4.183:

Offset	Size	Field	Type	Description
data+0	2	`fLockObj`	u16 LE (Boolean)	MUST be 0x0001. Objects on the sheet are protected.

This record exists if and only if the sheet is protected AND the objects on the sheet are protected. No independent password — uses the sheet's Password record.

ScenarioProtect — record type 221 (0x00DD) [MS-XLS] §2.4.245:

Offset	Size	Field	Type	Description
data+0	2	`fScenProtect`	u16 LE (Boolean)	0x0000 = scenarios not protected; 0x0001 = scenarios protected

No independent password — uses the sheet's Password record.

Prot4Rev — record type 431 (0x01AF) [MS-XLS] §2.4.205:

Offset	Size	Field	Type	Description
data+0	2	`fRevLock`	u16 LE (Boolean)	0x0000 = removal of shared workbook revision logs is allowed; 0x0001 = removal is disallowed

ABNF context [MS-XLS] §2.1.7.20: These records appear in a fixed sequence within the Globals substream as the PROTECTION production:

PROTECTION = WinProtect Protect Password Prot4Rev Prot4RevPass

In sheet substreams, the production is [MS-XLS] §2.1.7.20:

PROTECTION = [Protect] [ScenarioProtect] [ObjProtect] [Password]

FeatProtection Structure (.xls)¶

The FeatProtection structure is carried in the rgbFeat field of a Feat record (0x0868) when isf = ISFPROTECTION (0x0002) [MS-XLS] §2.5.124. It specifies password-protected editable ranges on a protected sheet.

Offset	Size	Field	Type	Description
0 (bit 0)	1 bit	`fSD`	bit	1 = structure contains self-relative security descriptor data in `sdContainer`
0 (bits 1-31)	31 bits	reserved	bits	MUST be zero
4	4	`wPassword`	u32 LE	Password verifier for editing referenced ranges. 0x00000000 = empty password. Stores the 16-bit Password Verifier Algorithm result zero-extended to 32 bits [MS-XLS] §2.2.9.
8	variable	`stTitle`	XLUnicodeString	Title for this protection feature (unique per sheet)
variable	variable	`sdContainer`	SDContainer	Security descriptor identifying users who can edit ranges without a password

The SDContainer sub-structure [MS-XLS] §2.5.234:

Offset	Size	Field	Type	Description
0	4	`cbSD`	u32 LE	Size of `sd` field in bytes. MUST be > 20.
4	`cbSD`	`sd`	SECURITY_DESCRIPTOR	Self-relative security descriptor per [MS-DTYP] §2.4.6, containing a DACL that lists SIDs for users/groups who may edit the range without entering a password

The Feat record itself [MS-XLS] §2.4.111:

Offset	Size	Field	Type	Description
0	12	`frtHeader`	FrtHeader	`frtHeader.rt` MUST be 0x0868
12	2	`isf`	u16 LE (SharedFeatureType)	MUST be `ISFPROTECTION` (0x0002) for protection
14	1	`reserved1`	u8	MUST be zero
15	4	`reserved2`	u32 LE	MUST be zero
19	2	`cref`	u16 LE	Number of `Ref8U` elements in `refs`
21	4	`cbFeatData`	u32 LE	MUST be zero when `isf` = `ISFPROTECTION`
25	2	`reserved3`	u16 LE	MUST be zero
27	variable	`refs`	Ref8U[]	Array of cell ranges (count = `cref`)
variable	variable	`rgbFeat`	FeatProtection	Protection data (structure above)

The corresponding FeatHdr record (0x0867) in the Globals substream carries EnhancedProtection in its rgbHdrData when isf = ISFPROTECTION [MS-XLS] §2.5.104. This is a 4-byte bitmask with 15 permission flags:

Bit	Field	Meaning (0 = action prevented, 1 = allowed)
0	`iprotObjects`	Whether linked/embedded objects can be edited
1	`iprotScenarios`	Whether scenarios can be edited
2	`iprotFormatCells`	Whether cells can be formatted
3	`iprotFormatColumns`	Whether columns can be formatted
4	`iprotFormatRows`	Whether rows can be formatted
5	`iprotInsertColumns`	Whether columns can be inserted
6	`iprotInsertRows`	Whether rows can be inserted
7	`iprotInsertHyperlinks`	Whether hyperlinks can be inserted
8	`iprotDeleteColumns`	Whether columns can be deleted
9	`iprotDeleteRows`	Whether rows can be deleted
10	`iprotSelLockedCells`	Whether locked cells can be selected
11	`iprotSort`	Whether cells can be sorted
12	`iprotAutoFilter`	Whether cells can be filtered
13	`iprotPivotTables`	Whether PivotTable reports can be created/modified
14	`iprotSelUnlockedCells`	Whether unlocked cells can be selected
15-31	reserved	MUST be zero

OOXML Protection Elements — XML Examples¶

The base protection elements are defined in [ISO/IEC 29500-1:2016]; [MS-XLSX] extends only protectedRange. [MS-OE376] documents Office-specific behavior for all elements.

<sheetProtection> — worksheet protection [ISO/IEC 29500-1] §3.3.1.81, [MS-OE376] §2.1.681:

<!-- ISO hash (modern) -->
<sheetProtection
    sheet="1"
    objects="1"
    scenarios="1"
    formatCells="0"
    formatColumns="0"
    formatRows="0"
    insertColumns="0"
    insertRows="0"
    insertHyperlinks="0"
    deleteColumns="0"
    deleteRows="0"
    selectLockedCells="0"
    sort="0"
    autoFilter="0"
    pivotTables="0"
    selectUnlockedCells="0"
    algorithmName="SHA-512"
    hashValue="TI4jF..."
    saltValue="rNh+..."
    spinCount="100000"/>

<!-- Legacy 16-bit verifier only -->
<sheetProtection
    sheet="1"
    objects="1"
    scenarios="1"
    password="CC40"/>

Boolean attributes default to false (0) except sheet, objects, and scenarios which default to false but MUST be true when the algorithmName or password attribute is present [MS-OE376] §2.1.681. A value of 1 for formatCells, sort, etc. means that action is allowed despite protection being active.

<workbookProtection> — workbook structure/revision protection [ISO/IEC 29500-1] §3.2.29, [MS-OE376] §2.1.621:

<workbookProtection
    lockStructure="1"
    lockWindows="0"
    lockRevision="1"
    workbookAlgorithmName="SHA-512"
    workbookHashValue="abc123..."
    workbookSaltValue="def456..."
    workbookSpinCount="100000"
    revisionsAlgorithmName="SHA-512"
    revisionsHashValue="789ghi..."
    revisionsSaltValue="jkl012..."
    revisionsSpinCount="100000"/>

<!-- Legacy 16-bit verifiers only -->
<workbookProtection
    lockStructure="1"
    workbookPassword="E7A3"
    revisionsPassword="F1B2"/>

The workbook* attributes protect workbook structure (sheets). The revisions* attributes protect change tracking history in shared workbooks. Per [MS-OE376] §2.1.621(d), Office uses workbookPassword for unlocking structure/windows (not revisions, despite the attribute's name in the standard).

<protectedRange> — editable ranges on a protected sheet [ISO/IEC 29500-1] §3.3.1.69, [MS-XLSX] §2.6.56:

<protectedRanges>
    <!-- ISO hash -->
    <protectedRange
        name="EditableArea"
        sqref="A1:D10 F1:F10"
        algorithmName="SHA-512"
        hashValue="base64encodedHash..."
        saltValue="base64encodedSalt..."
        spinCount="100000"
        securityDescriptor="O:WDG:WDD:(A;;CC;;;S-1-5-21-...)"/>

    <!-- Legacy 16-bit verifier -->
    <protectedRange
        name="LegacyRange"
        sqref="G1:G50"
        password="A1B2"/>
</protectedRanges>

The password and algorithmName attributes are mutually exclusive [MS-XLSX] §2.6.56. If algorithmName is present, then hashValue, saltValue, and spinCount MUST all be present. The securityDescriptor attribute is an SDDL string [MS-DTYP] §2.5.1 listing users who can edit the range without providing a password.

<fileSharing> — write reservation [ISO/IEC 29500-1] §3.2.12, [MS-OE376] §2.1.607:

<!-- ISO hash -->
<fileSharing
    userName="JDoe"
    readOnlyRecommended="1"
    algorithmName="SHA-512"
    hashValue="base64hash..."
    saltValue="base64salt..."
    spinCount="100000"/>

<!-- Legacy 16-bit verifier -->
<fileSharing
    userName="JDoe"
    readOnlyRecommended="1"
    reservationPassword="C8D2"/>

Dual-Hash Caveat¶

[MS-XLSX] §2.6.56 and [MS-XLSB] §2.2.10 document a critical ambiguity in how Office may compute the ISO password hash. Under circumstances specified in [MS-OFFCRYPTO] §1.3.4, the password is first converted to a 16-bit verifier value (via the Password Verifier Algorithm / CreatePasswordVerifier_Method1 in [MS-OFFCRYPTO] §2.3.7.1), then that 16-bit value is reinterpreted as a single Unicode character, and that character is passed to the ISO hash algorithm ([MS-OFFCRYPTO] §2.4.2.4).

There is no way to determine which method was used to generate a stored hash without knowledge of the password. A toolkit MUST compute both hashes and accept a match from either path:

Standard path: full Unicode password string fed directly into H(salt + password), iterated spinCount times.
Legacy-compatible path: Unicode password -> 16-bit verifier (via [MS-OFFCRYPTO] §2.3.7.1) -> reinterpret the 16-bit value as a single UTF-16LE character -> feed that character into H(salt + character), iterated spinCount times.

If either computed hash matches the stored hashValue, the password is valid. This dual-path requirement applies to <sheetProtection>, <workbookProtection>, <protectedRange>, <fileSharing>, and all their .xlsb Brt*Iso equivalents.

VelvetSweatshop Trigger Conditions¶

The default password "VelvetSweatshop" (\x56\x65\x6C\x76\x65\x74\x53\x77\x65\x61\x74\x73\x68\x6F\x70) is used to auto-encrypt the entire document when a protection record carries a non-zero verifier but no user-supplied open password was set. The following table lists every record/field combination that triggers this behavior:

Format	Record / Element	Field	Trigger condition	Spec reference
.xls	Password (0x0013) in Globals substream	`wPassword`	!= 0x0000	[MS-XLS] §2.4.191, product note <100>
.xls	Prot4RevPass (0x01BC)	`protPwdRev`	!= 0x0000	[MS-XLS] §2.4.206, product note <104>
.xlsb	BrtBookProtection (type 534)	`protpwdBook`	!= 0x0000	[MS-XLSB] §2.4.308, product note <25>
.xlsb	BrtBookProtection (type 534)	`protpwdRev`	!= 0x0000	[MS-XLSB] §2.4.308, product note <26>
.xlsb	BrtBookProtectionIso (type 677)	`ipdBookPasswordData.rgbHash`	non-empty (cbLength > 0)	[MS-XLSB] §2.4.309, product note <27>
.xlsb	BrtBookProtectionIso (type 677)	`ipdRevPasswordData.rgbHash`	non-empty (cbLength > 0)	[MS-XLSB] §2.4.309, product note <28>

Applies to: Excel 2007, Excel 2010, Excel 2013 per [MS-OFFCRYPTO] §2.4.2.3, Appendix A notes <24>-<25>.
The encryption method used is ECMA-376 Document Encryption as specified in [MS-OFFCRYPTO] §2.3.4.
Always attempt decryption with "VelvetSweatshop" first on any encrypted Excel file before password-cracking attempts. If decryption succeeds, the file has only strippable protection, not a real user-chosen open password.

.xlsb Binary Record Structures¶

.xlsb files use binary Brt* records instead of XML elements. Each protection gate has a legacy record and an ISO-compatible record; the ISO record MUST be immediately followed by its legacy counterpart with the password field zeroed out and all non-password fields duplicated [MS-XLSB] §2.4.309, §2.4.784, §2.4.343, §2.4.672, §2.4.756, §2.4.757.

BrtBookProtection (type 534, 6 bytes) [MS-XLSB] §2.4.308:

Offset	Size	Field	Type	Description
0	2	`protpwdBook`	u16 LE	16-bit password verifier for structure/window protection. 0x0000 = no password.
2	2	`protpwdRev`	u16 LE	16-bit password verifier for revision protection. 0x0000 = no password.
4	2	`wFlags`	BookProtectionFlags	Bit 0: `fLockStructure`; Bit 1: `fLockWindow`; Bit 2: `fLockRevision`; Bits 3-15: reserved (zero).

BrtBookProtectionIso (type 677, variable) [MS-XLSB] §2.4.309:

Offset	Size	Field	Type	Description
0	4	`dwBookSpinCount`	u32 LE	Iteration count for `ipdBookPasswordData` hash. MUST NOT exceed 10,000,000.
4	4	`dwRevSpinCount`	u32 LE	Iteration count for `ipdRevPasswordData` hash. MUST NOT exceed 10,000,000.
8	2	`wFlags`	BookProtectionFlags	Same value as the trailing BrtBookProtection.wFlags.
10	variable	`ipdBookPasswordData`	IsoPasswordData	Structure/window protection hash. If `rgbHash` is empty, no password for structure (but then `ipdRevPasswordData.rgbHash` MUST be non-empty).
variable	variable	`ipdRevPasswordData`	IsoPasswordData	Revision protection hash. If `rgbHash` is empty, no password for revisions (but then `ipdBookPasswordData.rgbHash` MUST be non-empty).

BrtSheetProtection (type 535, 66 bytes) [MS-XLSB] §2.4.783:

Offset	Size	Field	Type	Description
0	2	`protpwd`	u16 LE	16-bit password verifier. 0x0000 = no password.
2	4	`fLocked`	u32 LE (Boolean)	1 = sheet is protected
6	4	`fObjects`	u32 LE (Boolean)	1 = editing objects allowed (inverted when `fLocked`=1)
10	4	`fScenarios`	u32 LE (Boolean)	1 = editing scenarios allowed (inverted when `fLocked`=1)
14	4	`fFormatCells`	u32 LE (Boolean)	1 = formatting cells allowed
18	4	`fFormatColumns`	u32 LE (Boolean)	1 = formatting columns allowed
22	4	`fFormatRows`	u32 LE (Boolean)	1 = formatting rows allowed
26	4	`fInsertColumns`	u32 LE (Boolean)	1 = inserting columns allowed
30	4	`fInsertRows`	u32 LE (Boolean)	1 = inserting rows allowed
34	4	`fInsertHyperlinks`	u32 LE (Boolean)	1 = inserting hyperlinks allowed
38	4	`fDeleteColumns`	u32 LE (Boolean)	1 = deleting columns allowed
42	4	`fDeleteRows`	u32 LE (Boolean)	1 = deleting rows allowed
46	4	`fSelLockedCells`	u32 LE (Boolean)	1 = selecting locked cells allowed
50	4	`fSort`	u32 LE (Boolean)	1 = sorting allowed
54	4	`fAutoFilter`	u32 LE (Boolean)	1 = AutoFilter allowed
58	4	`fPivotTables`	u32 LE (Boolean)	1 = PivotTable usage allowed
62	4	`fSelUnlockedCells`	u32 LE (Boolean)	1 = selecting unlocked cells allowed

BrtSheetProtectionIso (type 678, 68 bytes fixed + variable IsoPasswordData) [MS-XLSB] §2.4.784:

Offset	Size	Field	Type	Description
0	4	`dwSpinCount`	u32 LE	Iteration count. MUST NOT exceed 10,000,000.
4	64	flags	16 x u32 LE	Same 16 Boolean fields as BrtSheetProtection (`fLocked` through `fSelUnlockedCells`), same values
68	variable	`ipdPasswordData`	IsoPasswordData	Hash data. `rgbHash` MUST NOT be zero-length.

MUST be immediately followed by a BrtSheetProtection record whose protpwd = 0x0000 and whose 16 flag fields match.

BrtCsProtection (type 669, 10 bytes) [MS-XLSB] §2.4.342 — chart sheet protection:

Offset	Size	Field	Type	Description
0	2	`protpwd`	u16 LE	16-bit password verifier. 0x0000 = no password.
2	4	`fLocked`	u32 LE (Boolean)	1 = chart element changes prevented
6	4	`fObjects`	u32 LE (Boolean)	1 = graphic object changes prevented

BrtCsProtectionIso (type 679, 12 bytes fixed + variable IsoPasswordData) [MS-XLSB] §2.4.343:

Offset	Size	Field	Type	Description
0	4	`dwSpinCount`	u32 LE	Iteration count. MUST NOT exceed 10,000,000.
4	4	`fLocked`	u32 LE (Boolean)	Same as BrtCsProtection.fLocked
8	4	`fObjects`	u32 LE (Boolean)	Same as BrtCsProtection.fObjects
12	variable	`ipdPasswordData`	IsoPasswordData	Hash data. `rgbHash` MUST NOT be zero-length.

BrtFileSharing (type 548, variable) [MS-XLSB] §2.4.671:

Offset	Size	Field	Type	Description
0	2	`fReadOnlyRec`	u16 LE (Boolean)	1 = read-only recommended
2	2	`wResPass`	u16 LE	Write-reservation password verifier. 0x0000 = no password.
4	variable	`stUserName`	XLNullableWideString	User who set the write-reservation password. MUST NOT exceed 54 characters.

BrtFileSharingIso (type 676, variable) [MS-XLSB] §2.4.672:

Offset	Size	Field	Type	Description
0	4	`dwSpinCount`	u32 LE	Iteration count. MUST NOT exceed 10,000,000.
4	2	`fReadOnlyRec`	u16 LE (Boolean)	Same as BrtFileSharing.fReadOnlyRec
6	variable	`stUserName`	XLNullableWideString	Same as BrtFileSharing.stUserName. MUST NOT exceed 54 characters.
variable	variable	`ipdPasswordData`	IsoPasswordData	Hash data. `rgbHash` MUST NOT be zero-length.

BrtRangeProtection (type 536, variable) [MS-XLSB] §2.4.754:

Offset	Size	Field	Type	Description
0	2	`protPwd`	u16 LE	16-bit password verifier. 0x0000 = no password.
2	variable	`sqRfX`	UncheckedSqRfX	Cell ranges. `crfx` MUST be > 0 and < 8192.
variable	variable	`RangeProtectionTitleSDRel`	RangeProtectionTitleSDRel	Title (XLWideString, 1-255 chars, unique per sheet) + optional security descriptor (`dwsdRel` u32 LE = size, then SECURITY_DESCRIPTOR per [MS-DTYP] §2.4.6).

BrtRangeProtectionIso (type 680, variable) [MS-XLSB] §2.4.756:

Offset	Size	Field	Type	Description
0	4	`dwSpinCount`	u32 LE	Iteration count. MUST NOT exceed 10,000,000.
4	variable	`sqRfX`	UncheckedSqRfX	Same ranges as trailing BrtRangeProtection.
variable	variable	`RangeProtectionTitleSDRel`	RangeProtectionTitleSDRel	Same title/SD as trailing BrtRangeProtection.
variable	variable	`ipdPasswordData`	IsoPasswordData	Hash data. `rgbHash` MUST NOT be zero-length.

BrtRangeProtection14 (type 1103) and BrtRangeProtectionIso14 (type 1104) are identical to their non-14 counterparts but use an FRTHeader to encode the cell range when crfx >= 8192 [MS-XLSB] §2.4.755, §2.4.757.

IsoPasswordData Sub-Structure¶

IsoPasswordData [MS-XLSB] §2.5.80 is the variable-size structure holding the fields needed to verify a strong password hash:

Offset	Size	Field	Type	Description
0	variable	`rgbHash`	LPByteBuf	Password hash bytes
variable	variable	`rgbSalt`	LPByteBuf	Salt used in hash computation
variable	variable	`szAlgName`	XLNullableWideString	Name of the hash algorithm (e.g. `"SHA-512"`)

Consistency constraints [MS-XLSB] §2.5.80: - If rgbHash is non-empty, szAlgName MUST be non-empty. - If rgbSalt is non-empty, both rgbHash and szAlgName MUST be non-empty. - If szAlgName is non-empty, rgbHash MUST be non-empty.

Typical sizes: for SHA-512, rgbHash = 64 bytes, rgbSalt = 16 bytes, szAlgName = "SHA-512" (7 characters = 14 bytes UTF-16LE). Minimum size (empty/no-password): 12 bytes (three 4-byte zero-length prefixes).

LPByteBuf Encoding¶

LPByteBuf [MS-XLSB] §2.5.91 is a length-prefixed byte array:

Offset	Size	Field	Type	Description
0	4	`cbLength`	u32 LE	Number of bytes in the data array
4	`cbLength`	`rgbData`	byte[]	Raw binary data. Exactly `cbLength` bytes.

Total wire size: 4 + cbLength bytes.

XLNullableWideString Encoding¶

XLNullableWideString [MS-XLSB] §2.5.167 is a length-prefixed Unicode string that can represent NULL:

Offset	Size	Field	Type	Description
0	4	`cchCharacters`	u32 LE	Number of characters. 0xFFFFFFFF = NULL string (no character data follows).
4	`cchCharacters * 2`	`rgchData`	UTF-16LE	Unicode character data. If `cchCharacters` = 0xFFFFFFFF, this array is 0 bytes.

Total wire size: 4 + (cchCharacters * 2) bytes, or 4 bytes if NULL.

The non-nullable variant XLWideString [MS-XLSB] §2.5.169 uses the same layout but cchCharacters MUST be >= 0x00000000 and < 0xFFFFFFFF (NULL is not permitted).

OLE Stream Names¶

Special stream names within OLE/CFB containers for Excel files:

Stream/Storage name	Hex prefix	Purpose	Spec reference
`"Workbook"`	none	BIFF8 workbook stream (MUST be this name, not `"Book"`)	[MS-XLS] §2.1.7.20
`"Book"`	none	Legacy BIFF5/BIFF7 workbook stream; NOT valid for BIFF8 but tolerated by some readers	undocumented fallback
`"\x06DataSpaces"`	0x06	Data spaces storage; required for ECMA-376 encryption and IRM	[MS-OFFCRYPTO] §2.3.4.1, §2.2
`"EncryptionInfo"`	none	Encryption metadata stream within the data spaces framework; carries vMajor/vMinor + encryption header/XML	[MS-OFFCRYPTO] §2.3.4.5, §2.3.4.10
`"EncryptedPackage"`	none	The encrypted OPC ZIP package (for .xlsx/.xlsb with open password); the entire ZIP is encrypted as a single blob	[MS-OFFCRYPTO] §2.3.4.4
`"encryption"`	none	Encryption stream for RC4 CryptoAPI in .xls files; stores encrypted versions of other streams/storages	[MS-XLS] §2.1.7.6; [MS-OFFCRYPTO] §2.3.5.4
`"\x09DRMContent"`	0x09	IRM-protected content stream (DRM)	[MS-XLS] §2.1.7.13; [MS-OFFCRYPTO] §2.2.10
`"\x09DRMViewerContent"`	0x09	IRM viewer content stream	[MS-XLS] §2.1.7.19; [MS-OFFCRYPTO] §2.2.11
`"_signatures"`	none	CryptoAPI digital signature stream (legacy binary format)	[MS-OFFCRYPTO] §2.5.1
`"_xmlsignatures"`	none	XML digital signature storage (OOXML format)	[MS-OFFCRYPTO] §2.5.2
`"_VBA_PROJECT_CUR"` or `"VBA"`	none	VBA macro storage containing the `PROJECT` stream with DPB=/CMG=/GC= protection lines	[MS-OVBA] §2.2.1

Distinguishing encrypted .xlsx from plain .xlsx: an encrypted OOXML file (.xlsx/.xlsb/.xlsm) is NOT a ZIP on disk — it is re-wrapped in an OLE/CFB container. To distinguish: - Plain .xlsx: starts with ZIP magic bytes PK\x03\x04 (0x504B0304). The OPC package is the file itself. - Encrypted .xlsx: starts with OLE/CFB signature \xD0\xCF\x11\xE0\xA1\xB1\x1A\xE1. The CFB container holds \x06DataSpaces, EncryptionInfo, and EncryptedPackage streams. The EncryptedPackage stream, once decrypted, yields the original OPC/ZIP package. The file extension (.xlsx, .xlsb, .xlsm, .xltx) is preserved unchanged despite the container format change [MS-OFFCRYPTO] §2.3.4.