SMBIOS Identity Generation

What SMBIOS Identity Is

SMBIOS (System Management BIOS) provides hardware identity data that macOS reads during boot to determine what machine it is running on. macOS uses this data to:

• Select the correct kernel configuration and hardware drivers
• Validate hardware for Apple services (iMessage, FaceTime, iCloud)
• Apply model-specific power management and thermal profiles

In a VM, SMBIOS data must be injected via QEMU arguments so macOS sees a plausible Apple hardware identity. Without valid SMBIOS, macOS boots in a degraded state or refuses to activate services.

Identity Generation Flow

Generated Identity Fields

Field	Format	Purpose
Serial	12 chars	Apple hardware serial number
MLB	17 chars	Main Logic Board serial (with checksum)
UUID	Standard UUID v4	Unique machine identifier
ROM	6-byte hex	Derived from MAC address
Model	e.g. MacPro7,1	SMBIOS product name

All fields are represented in the SmbiosIdentity dataclass:

@dataclass
class SmbiosIdentity:
    serial: str
    mlb: str
    uuid: str
    rom: str
    model: str
    mac: str = ""

Serial Number Generation

Apple serial numbers follow a 12-character format encoding manufacturing metadata:

{country:3}{year:1}{week:1}{line:3}{model_code:4}

Segment	Length	Source
Country code	3	Manufacturing location (C02, C07, CK2)
Year char	1	Encoded from year via _YEAR_CHARS lookup table
Week char	1	Encoded from manufacturing week (1-52) using base-34
Line code	3	Production line number (0-3399) encoded as 3 base-34 digits
Model code	4	Hardware model identifier (e.g. P7QM for MacPro7,1)

Base-34 Alphabet

Apple uses a 34-character alphabet that excludes I and O to avoid ambiguity:

0123456789ABCDEFGHJKLMNPQRSTUVWXYZ

Year and Week Encoding

Year characters cycle every 10 years from 2010 using the lookup table CDFGHJKLMN. Weeks 1-26 use the base year character; weeks 27-52 advance the year character by one position. The week position within the half-year is encoded as a base-34 digit.

Production Line Encoding

The production line number (0-3399) is encoded as three base-34 digits using standard positional encoding:

d1 = line // (34 * 34)
d2 = (line // 34) % 34
d3 = line % 34

MLB Generation

The Main Logic Board serial is a 17-character string with a built-in checksum:

{country:3}{year_dec:1}{week_dec:2}{block1:3}{block2:2}{board:4}{block3:2}

Segment	Source
Country	Same manufacturing location as serial
Year/Week	Decimal-encoded manufacturing date
Block1	Random from pool (200, 600, 403, 404, etc.)
Block2	Random from pool (Q0-QZ in base-34)
Board	Board code for the model (e.g. K3F7 for MacPro7,1)
Block3	Computed analytically to satisfy mod-34 checksum

Mod-34 Checksum

The checksum uses an alternating weight scheme (3/1) across all characters:

def _verify_mlb_checksum(mlb: str) -> bool:
    checksum = 0
    for i, ch in enumerate(mlb):
        j = BASE34.index(ch)
        weight = 3 if ((i & 1) == (len(mlb) & 1)) else 1
        checksum += weight * j
    return checksum % 34 == 0

The final two characters (block3) are computed so the total weighted sum is divisible by 34. This matches the format Apple uses for genuine MLB serials.

ROM Derivation

The ROM field is a 6-byte value derived from the VM's MAC address by stripping the colon separators:

MAC: AA:BB:CC:DD:EE:FF -> ROM: AABBCCDDEEFF

This ties the SMBIOS identity to the VM's network interface, which macOS uses for hardware binding in Apple services.

Pure Python Implementation

The entire SMBIOS generation is implemented in Python using only standard library modules (secrets, string, uuid). There is no dependency on the external GenSMBIOS binary or any macOS-specific tools. All randomness uses secrets for cryptographic quality.

Platform Data

Model-specific manufacturing data is stored in APPLE_PLATFORM_DATA:

Model	Country Codes	Year Range	Board Code
MacPro7,1	C02, C07, CK2	2019-2023	K3F7

All supported macOS versions (Ventura through Tahoe) use MacPro7,1 as the SMBIOS model.