The reference implementation (svrooij/ContentPrep Zipper.cs DecryptFileAsync)
reads the first 32 bytes as the stored HMAC, then hashes the *remaining* bytes
— i.e. IV (16 bytes) || ciphertext — to verify integrity. ImpTune was computing
HMAC(mac_key, ciphertext) which omits the IV. Intune's server-side HMAC check
would therefore always fail, manifesting as the same silent symptom as the
Detection.xml bug: empty wizard fields, greyed OK button, no error banner.
The blob layout is unchanged: [HMAC(32)] + [IV(16)] + [ciphertext].
Only the hash input is corrected: iv + ciphertext instead of ciphertext.
The Mac field in Detection.xml is also updated accordingly (it stores the same
HMAC value that is prepended to the blob).
Tests updated: test_hmac_matches now verifies HMAC over blob[32:] (= IV+ciphertext),
which is exactly what the reference decryption algorithm verifies against.
All 114 tests pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Four structural defects in the generated Detection.xml caused Intune's upload
wizard to silently fail metadata parsing (empty form, OK button greyed):
1. Missing ToolVersion="1.8.6.0" XML attribute on ApplicationInfo — the wizard
uses this to validate the package was produced by a compatible tool.
2. Spurious xmlns="http://schemas.microsoft.com/IntuneWin" namespace — changes
element identity for Intune's XML parser (reference emits no namespace).
3. <?xml version="1.0" ?> declaration header — reference uses OmitXmlDeclaration=true.
4. Extra <MacAlgorithm> child element inside EncryptionInfo — not present in
the reference FileEncryptionInfo model (svrooij/ContentPrep verified).
Fix: switched from toprettyxml() to tostring(xml_declaration=False)+indent(),
added ToolVersion attribute, removed xmlns and MacAlgorithm.
Tests updated to assert the corrected reference format; all 114 pass.
Root cause verified against svrooij/ContentPrep Packager.cs + ApplicationInfo.cs
(open-source C# reference implementation of IntuneWinAppUtil.exe).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- AES-256-CBC encryption with PKCS7 padding using pycryptodome
- HMAC-SHA256 of ciphertext prepended to blob (mac_key, 32 bytes)
- Encrypted blob layout: HMAC(32) + IV(16) + ciphertext
- IV is 16 bytes (corrected from STACK.md documentation error of 32 bytes)
- Detection.xml with all 8 EncryptionInfo sub-elements and correct namespace
- Inner ZIP uses DEFLATE compression; outer ZIP uses STORED compression
- All 14 byte-level tests pass including crypto roundtrip verification
kawaandClaude Sonnet 4.6