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fairplay-scinfo

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File-format documentation and ImHex patterns for Apple FairPlay's SC_Info files (.supx/.supp/.supf/.v4.supp/.v5.supf/.sinf), including the new v4/v5 formats.

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Documentation and [ImHex](https://imhex.werwolv.net/) pattern files for the Apple
FairPlay protection files that ship in every iOS app bundle's `SC_Info/` directory:
`.supx`, `.supp`, `.supf`, `.v4.supp`, `.v5.supf`, `.sinf`, and `Manifest.plist`.
Together these carry the per-page content keys, the signing certificate, and the
DRM scheme info that let iOS decrypt and validate each Mach-O binary in the app.

## Motivation

This research was inspired by the recent change to the **new FairPlay file
formats**. Apple introduced the `.v4.supp` (`0x04`) and `.v5.supf` (`0x05`)
variants and stops shipping the legacy
`.supp` (`0x01`) / drops the legacy `.supf` (`0x03`) to 0 bytes. We set out to
document both generations and understand exactly what differs between them.

Apps where this shows up include:

- **`com.microsoft.rdc.ios` 11.3.2** - main binary
- **`com.gopro.GoPro` 13.34.1** - `ReelSteady.framework`

In both, the legacy `.supp` is missing and `.supf` is 0 bytes, while the current
`.v4.supp` / `.v5.supf` / `.supx` are present, and the binaries run normally.

## Format overview

A fully populated `SC_Info` contains:

| File | ver byte | role | class | generation |
|------|----------|------|-------|------------|
| `<Name>.supx` | - | tagged index of key fingerprints | x | - |
| `<Name>.supp` | `0x01` | per-page keys + cert + signature | p | old |
| `<Name>.supf` | `0x03` | per-page keys + cert + signature | f | old |
| `<Name>.v4.supp` | `0x04` | per-page keys + cert + signature | p | new |
| `<Name>.v5.supf` | `0x05` | per-page keys + cert + signature | f | new |
| `<Name>.sinf` | - | DRM scheme info (account/rights + AES IV) | - | - |
| `Manifest.plist` | - | `.sinf` source + replication paths | - | - |

- **Two classes, two generations.** `.supp`/`.v4.supp` are the **p-class** and
  `.supf`/`.v5.supf` the **f-class** - two different containers around the same
  per-page keys. This architectural shift is orthogonal to the format generations: the only structural difference is that older variants include a SHA-1 hash, which the newer files omit.
- **Per-page keys.** Each key file holds a table of 32-byte (256-bit) keys, one per
  4 KB page. The f-class covers only the FairPlay-encrypted pages (`npages =
  cryptsize/4096`); the p-class covers every page from offset 0 (header + encrypted),
  so the f-class table is the encrypted-page tail of the p-class table.
- **The 20-byte block** distinguishing the pre-26 files is a SHA-1 of the binary's
  Mach-O **code-signature blob** (the `LC_CODE_SIGNATURE` / `0xfade0cc0` superblob) -
  a content-integrity hash.
- **Cert + signature.** Both classes end with a 708-byte X.509 RSA-1024 FairPlay
  leaf certificate (drawn from a reused pool of 13 signing identities) and a 128-byte RSA-1024 signature
  bound to the file.
- **`.supx`** is a self-describing (TLV) index and a per-app constant. **`.sinf`** is
  an MP4/iTunes atom tree (authored once and replicated per binary) carrying the
  account/rights dictionary and a 16-byte AES IV.
- **Magic.** The version byte is followed by a 3-byte tag, `36 31 32` (`"612"`) for our sample; earlier research by pwn0rz reported `507`.

### Container layouts

**f-class** (`.supf` / `.v5.supf`) - a length-value container:

```
0x00  u8      version            0x03 or 0x05
0x01  3       magic
0x04  KeyPairSegments
        u32   length             total length of nseg + all segments
        u32   nseg               segment count (1 per architecture; >1 for fat)
        Segment[nseg]
          u32      length        length of the fields below
          u32      cpu_type      0x0100000c = ARM64, 0x0000000c = ARM32
          u32      cpu_subtype   0/1 arm64, 2 arm64e, ...
          u8[20]   sha1_hash     SHA-1(Mach-O code signature) - v03 ONLY (omitted in v05)
          u32      npages        number of 4 KB encrypted pages
          u8[*]    key_data      npages × 32 bytes
      CertificateLV   u32 length (708) + DER cert
      SignatureLV     u32 length (128) + RSA-1024 signature
```

**p-class** (`.supp` / `.v4.supp`) - a page-indexed key table:

```
0x00  u8      version            0x01 or 0x04
0x01  3       magic
0x04  u8[20]  sha1_hash          SHA-1(Mach-O code signature) - v01 ONLY (omitted in v04)
0x..  u32     count              total pages = (cryptoff + cryptsize) / 4096
0x..  PageKey page_keys[count]   32 bytes per page, from file offset 0:
                                   [0 .. cryptoff/4096)  header pages (4)
                                   [cryptoff/4096 .. )   encrypted pages == f-class key_data
0x..  CertificateLV              u32 length (708) + DER cert
0x..  u8[128] signature          RSA-1024 signature (raw, no length prefix)
```

### Certificate + signature trailer

The trailer begins at the marker `00 00 02 C4  30 82 02 C0` (certLen 708 + DER
`Certificate SEQUENCE`), present in every key file:

```
certLen       4 B   = 00 00 02 C4 (708)
certificate 708 B   X.509 RSA-1024 leaf cert (from a reused pool of 13)
signature           p-class: 128 B raw RSA-1024
                    f-class: 00 00 00 80 (len) + 128 B RSA-1024
```

### `.sinf` (DRM scheme info)

An MP4/iTunes atom tree - `be u32 size` (incl. the 8-byte header) + 4-char `type` +
payload, nested:

```
sinf
  frma  <4cc>                       original data format
  schm  00000000 "itun" 00000000    scheme = iTunes FairPlay
  schi                              scheme info:
    user / crdt / asdt / key  u32   account id / dates / key index
    iviv  u8[16]                    16-byte AES IV
    righ  { 4cc -> u32 }*           rights dictionary (veID, plat, aver, tran, tool, ...)
    name  cstring                   account name
    priv  u8[*]                     encrypted private data
  sign  u8[*]                       signature
```

### `.supx` index

Self-describing via its length fields:

```
0x00  u32  formatTag      1
0x04  u32  trailerOffset  0x40 -> offset of the trailer below (one-entry TOC)
0x08  u32  entry0.count   1
0x0C  u32  entry0.length  0x10 (16)
0x10  16B  entry0.data    key fingerprint
0x20  u32  entry1.type    2
0x24  u32  entry1.length  0x10 (16)
0x28  16B  entry1.data    key fingerprint
0x38  8B   padding        zero (aligns trailer to 0x40)
0x40  16B  trailer        MAC / integrity digest over the index
```

## Contents

| Path | Description |
|------|-------------|
| [`patterns/supx.hexpat`](patterns/supx.hexpat) | The `.supx` index |
| [`patterns/supp.hexpat`](patterns/supp.hexpat) | p-class key files (`.supp` / `.v4.supp`) |
| [`patterns/supf.hexpat`](patterns/supf.hexpat) | f-class key files (`.supf` / `.v5.supf`) |
| [`patterns/sinf.hexpat`](patterns/sinf.hexpat) | `.sinf` DRM scheme info (MP4 atom tree, incl. the rights dictionary) |

## Using the ImHex patterns

Open a target file in [ImHex](https://imhex.werwolv.net/) and load the matching
pattern (File → Import → Pattern File, or paste it into the pattern editor).

## Sample files

This repository does **not** provide any concrete `SC_Info` files. 
To obtain these, you can use [ipatool](https://github.com/majd/ipatool).

## Related work

Complementary to pwn0rz's FairPlay research, which documents the same family from a
different angle:
https://github.com/pwn0rz/fairplay_research

Prior efforts regarding .sinf modification:
https://github.com/roothide/FairFree

## Scope

This research documents **file formats**. It does **not** circumvent FairPlay: the per-page
keys are wrapped, and the certificate + RSA-1024 signature are bound to a private key
held only by the signer.

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