Rairii, 1 year ago

// #RaspberryPi codec licensing serial algo (<=RPi3)
// shoutouts to fabien perigaud/synacktiv. your beerump 2017 presentation slides started me on this journey.
// (sure you redacted the fun stuff, I just rediscovered it myself)
// also shoutouts to everyone involved in BCM2708 reversing!
// greetings to elites, fuckings to lamers (second category includes broadcom and rpi foundation)

??=include <stdint.h>
??=include <stdio.h>

typedef uint8_t u8;
typedef uint16_t u16;
typedef uint32_t u32;

u8 vce_data[] = {
0x54, 0x6f, 0x76, 0x6b, 0x94, 0xce, 0x1a, 0x57, 0x56, 0x51, 0x0c, 0xb2, 0x72, 0xc9, 0xc3, 0x12,
0x13, 0xbc, 0xe8, 0xd2, 0x5b, 0xa3, 0x2d, 0x2a, 0x5a, 0x62, 0x4d, 0xeb, 0x16, 0x40, 0x05, 0x87,
0xe0, 0x98, 0x39, 0xf7, 0xac, 0xc6, 0xab, 0x7c, 0xe9, 0xfb, 0x07, 0xaa, 0x29, 0xcd, 0x1d, 0x9b,
0xf6, 0x0e, 0x01, 0xbb, 0x5c, 0xfc, 0x15, 0xae, 0xd9, 0xfa, 0x9c, 0xef, 0xf1, 0x75, 0x8e, 0x70,
0x46, 0x8b, 0xb0, 0x89, 0x50, 0xaf, 0x6e, 0x67, 0x18, 0xda, 0xee, 0xd4, 0x32, 0xbe, 0x4e, 0x58,
0x5d, 0x1f, 0x4b, 0x73, 0x88, 0xc0, 0x79, 0x02, 0xde, 0x47, 0xa0, 0x43, 0x9a, 0xdb, 0xc8, 0x35,
0x95, 0x3c, 0xcc, 0x8d, 0x64, 0x2f, 0x14, 0x68, 0x00, 0x71, 0x03, 0xb9, 0xed, 0x0b, 0xf3, 0x24,
0x60, 0xb1, 0x17, 0x63, 0xdf, 0x48, 0x41, 0xa4, 0x28, 0x5e, 0x2b, 0xd8, 0xb4, 0x90, 0xba, 0x83,
0xe4, 0x08, 0xd0, 0xe2, 0xb8, 0x6a, 0x10, 0x74, 0x9f, 0x7b, 0x19, 0x38, 0x8f, 0x91, 0xd6, 0xa8,
0x27, 0x06, 0x30, 0x33, 0x61, 0x34, 0x25, 0x21, 0x53, 0xc7, 0x66, 0x23, 0xff, 0xc5, 0x80, 0x85,
0xf4, 0xd7, 0x97, 0x99, 0x55, 0xf2, 0x8c, 0x04, 0x6c, 0x4f, 0xa1, 0x36, 0x20, 0x0a, 0xe1, 0x44,
0x59, 0xcf, 0x7d, 0xb6, 0xf9, 0x0f, 0x6d, 0x11, 0x78, 0x93, 0xe5, 0x3f, 0xf0, 0x9e, 0x84, 0xd3,
0x7e, 0xbd, 0xd1, 0xf5, 0xa5, 0x81, 0x22, 0x37, 0xf8, 0x52, 0xe3, 0x5f, 0xa9, 0xca, 0xfd, 0x42,
0x7f, 0x09, 0xa2, 0x9d, 0x8a, 0xb7, 0x4a, 0xe6, 0xa6, 0x77, 0x3d, 0x1c, 0x2e, 0xcb, 0x1b, 0x69,
0xb3, 0x1e, 0xc1, 0x7a, 0x82, 0xdd, 0x2c, 0xdc, 0x49, 0xea, 0x3a, 0xe7, 0x31, 0x4c, 0xad, 0xbf,
0x0d, 0xc2, 0xc4, 0x96, 0x65, 0x26, 0xfe, 0x92, 0x86, 0x3b, 0x3e, 0xec, 0xd5, 0xb5, 0xa7, 0x45
};

??=define INLINE static inline attribute ((optimize (3))) attribute((always_inline))

INLINE u32 GET(u32 var, u8 bits) {
return vce_data[(var >> bits) & 0xff] << bits;
}

// should probably use bitwise OR, but this is what the vce code does
INLINE u32 GET32(u32 var) {
return GET(var,24) ^ GET(var,16) ^ GET(var,8) ^ GET(var,0);
}

// vce has no rotate instructions, so it does it the long way as in C
INLINE u32 ROR(u32 var, u32 right) {
return (var >> right) ^ (var << (32 - right));
}

u32 codec_license_hash(u32 board_serial /* r1 /,u32 codec / r2 */) {

??=define CODEC_XOR_BOARD_ROR(bits) codec ^= ROR(board_serial,bits)
??=define BOARD_XOR_CODEC_ROR(bits) board_serial ^= ROR(codec,bits)

for (u32 i = 0; i < 17; i++) {
CODEC_XOR_BOARD_ROR(1);
BOARD_XOR_CODEC_ROR(6);
CODEC_XOR_BOARD_ROR(13);
BOARD_XOR_CODEC_ROR(17);
CODEC_XOR_BOARD_ROR(21);
BOARD_XOR_CODEC_ROR(29);

board_serial = GET32(board_serial);
codec = GET32(codec);
}

??=undef CODEC_XOR_SHIFTS_BOARD
??=undef BOARD_XOR_SHIFTS_CODEC

return codec;
}

// This board serial taken from hxxps://web.archive.org/web/20221208160705/forums.raspberrypi.com/viewtopic.php?t=38901
// The person who owns the SoC with this serial burned in fuses did a nice thing and provided their own WVC1 + MPG2 keys, we can use that to verify this implementation is correct:
// decode_MPG2=0x6fd66307
// decode_WVC1=0x01a512b0
??=define BOARD_SERIAL 0x9d3e8cb1

void main() {
printf("??= VC1 key\ndecode_WVC1=0x%08x\n\n", codec_license_hash(BOARD_SERIAL, 0xf00bad34 ^ 0x57564331 /* 'WVC1' /));
printf("??= MPEG-2 key\ndecode_MPG2=0x%08x\n\n", codec_license_hash(BOARD_SERIAL, 0xf00bad34 ^ 0x4D504732 / 'MPG2 /));
printf("??= Super-secret key ;)\n??=\n"
"??= start.elf, before booting ARM, reads bootsig key from efuses, then compares against 1/2 of 5 hardcoded keys.\n"
"??= If not equal, then this key is checked, if not correct then infinite loop + LED flash\n"
"??= (same as if 3rdsig -- ARM kernel binary HMAC signature -- verification fails)\n"
"??= As to why this is done, I have no idea. Bootsig key is also 128-bit HMAC key and this reduces the available\n"
"??= possible entropy for unique bootsig key (necessary for boot-time security I would think!) down to either\n"
"??= 51, 52, or 77 bits depending on what key was burned into your Pi's efuses...\n"
"decode_0001=0x%08x\n\n", codec_license_hash(BOARD_SERIAL, 0xf00bad34 ^ 0x30303031 / '0001' */));
}