[
  {
    "path": "README.md",
    "content": "Samsung Firmware Magic\n======================\n\nSamsung distributes firmware updates for their SSDs for either \"Windows\" or\n\"Mac\". Ironically, both of these are bootable Linux `.iso` files, containing the\nactual firmware and update program.\n\nThe `.iso` files can be unpacked, but ultimately we end up with an obfuscated\nbinary blob, even for the meta information.\n\nFor the upstream file downloads, see\n\n    https://www.samsung.com/semiconductor/minisite/ssd/download/tools/\n\nOut of curiosity, I decided to create a decryption tool for this obfuscated\nformat, which is found in this repository.\n\nUnpacking iso image to firmware blob\n------------------------------------\n\nFirst, we download a firmware iso:\n\n    `wget http://downloadcenter.samsung.com/content/FM/201711/20171102105105735/Samsung_SSD_850_PRO_EXM04B6Q_Win.iso`\n\nNext, we unpack the relevant file from the iso, the `initrd`:\n\n    `7z x Samsung_SSD_850_PRO_EXM04B6Q_Win.iso initrd`\n\nThis file is a gzip-compressed cpio archive, so use 7z to strip gzip:\n\n    `7z x initrd`\n\nThis produces `initrd~`, containing the uncompressed contents. From here we\nextract the directory of interest, `root/fumagician`:\n\n    `7z -ofw x 'initrd~' root/fumagician`\n\nThis creates `fw/root/fumagician` in the current directory:\n\n```\n$ cd fw/root/fumagician\n$ ls -l\ntotal 5408\n-rw-rw-r-- 1 user user    2124 1971-03-22 19:52 DSRD.enc\n-rw-rw-r-- 1 user user 4752867 1971-03-22 19:52 EXM04B6Q.enc\n-rw-rw-r-- 1 user user  772516 2016-10-14 10:42 fumagician\n-rw-rw-r-- 1 user user     290 2016-10-14 10:42 fumagician.sh\n```\n\nThe files `DSRD.enc` (xml list of firmwares) and `EXM04B6Q.enc` (firmwares)\nare the obfuscated files, that we can now decrypt.\n\nDecrypting firmware blob\n------------------------\n\nThe included `decode.py` script will unpack these `.enc` files, like so:\n\n```shell\n## show xml on stdout:\n$ ./samsung-magic.py < fw/root/fumagician/DSRD.enc\n\n## decrypt firmware to file:\n$ ./samsung-magic.py < fw/root/fumagician/EXM04B6Q.enc > EXM04B6Q.bin\n```\n\nSeemingly, the folks at Samsung are huge fans of nesting things, because the\ndecrypted `EXM04B6Q.bin` file is actually a zip file, containing encrypted\nfirmware files:\n\n```shell\n$ unzip -l EXM04B6Q.bin\nArchive:  EXM04B6Q.bin\n  Length      Date    Time    Name\n---------  ---------- -----   ----\n  1048576  2017-02-19 10:41   EXM04B6Q_10170217.enc\n  1048576  2017-02-19 10:41   EXM04B6Q_20170203.enc\n  1048576  2017-02-19 10:41   EXM04B6Q_30170203.enc\n  1048576  2017-02-19 10:41   EXM04B6Q_40170902.enc\n  1048576  2017-02-19 10:41   EXM04B6Q_50170208.enc\n  1048576  2017-02-19 10:41   EXM04B6Q_60170208.enc\n---------                     -------\n  6291456                     6 files\n```\n\nLuckily, the encryption is exactly the same, so `samsung-magic.py` can decrypt\nthese as well:\n\n```\n$ unzip EXM04B6Q.bin\n$ ./samsung-magic.py < EXM04B6Q_10170217.enc > EXM04B6Q_10170217.bin\n```\n\nNow, at last, we have the raw firmware.\n\nEnjoy!\n"
  },
  {
    "path": "samsung-magic.py",
    "content": "#!/usr/bin/env python3\n\nfrom sys import stdin, stdout\nfrom struct import pack\nfrom Crypto.Cipher import AES\n\n## this is the shuffle map that samsung uses\nshuffle = bytes([\n           0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19,\n           0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x30, 0x31, 0x32, 0x33,\n           0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D,\n           0x3E, 0x3F, 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57,\n           0x58, 0x59, 0x5A, 0x5B, 0x5C, 0x5D, 0x5E, 0x5F, 0x70, 0x71,\n           0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A, 0x7B,\n           0x7C, 0x7D, 0x7E, 0x7F, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95,\n           0x96, 0x97, 0x98, 0x99, 0x9A, 0x9B, 0x9C, 0x9D, 0x9E, 0x9F,\n           0xB0, 0xB1, 0xB2, 0xB3, 0xB4, 0xB5, 0xB6, 0xB7, 0xB8, 0xB9,\n           0xBA, 0xBB, 0xBC, 0xBD, 0xBE, 0xBF, 0xD0, 0xD1, 0xD2, 0xD3,\n           0xD4, 0xD5, 0xD6, 0xD7, 0xD8, 0xD9, 0xDA, 0xDB, 0xDC, 0xDD,\n           0xDE, 0xDF, 0xF0, 0xF1, 0xF2, 0xF3, 0xF4, 0xF5, 0xF6, 0xF7,\n           0xF8, 0xF9, 0xFA, 0xFB, 0xFC, 0xFD, 0xFE, 0xFF, 0xE0, 0xE1,\n           0xE2, 0xE3, 0xE4, 0xE5, 0xE6, 0xE7, 0xE8, 0xE9, 0xEA, 0xEB,\n           0xEC, 0xED, 0xEE, 0xEF, 0xC0, 0xC1, 0xC2, 0xC3, 0xC4, 0xC5,\n           0xC6, 0xC7, 0xC8, 0xC9, 0xCA, 0xCB, 0xCC, 0xCD, 0xCE, 0xCF,\n           0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0xA6, 0xA7, 0xA8, 0xA9,\n           0xAA, 0xAB, 0xAC, 0xAD, 0xAE, 0xAF, 0x80, 0x81, 0x82, 0x83,\n           0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8A, 0x8B, 0x8C, 0x8D,\n           0x8E, 0x8F, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67,\n           0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F, 0x40, 0x41,\n           0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4A, 0x4B,\n           0x4C, 0x4D, 0x4E, 0x4F, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25,\n           0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F,\n           0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,\n           0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F\n])\n\n## generate reverse map\nlookup = bytes(shuffle.find(i) for i in range(256))\n\n## utility functions\ndef xor(s1, s2):\n    return bytes(a ^ b for a,b in zip(s1, s2))\n\ndef unshuffle(s):\n    return bytes(lookup[c] for c in s)\n\n## crypto constants\niv0 = bytes.fromhex(\"8ce82eefbea0da3c44699ed7\")\nkey = bytes.fromhex(\"56e47a38c5598974bc46903dba290349\")\nctr = 0\naes = AES.new(key, AES.MODE_ECB)\n\nwhile True:\n    ## read next aes block\n    blk = stdin.buffer.read(16)\n    if len(blk) == 0:\n        break\n\n    ## samsung arbitrarily resets the counter every 32 blocks\n    ctr = (ctr % 32) + 1\n\n    iv = iv0 + pack(\">I\", ctr)\n\n    ## we are using ECB mode to simulate the 32-block CTR mode\n    ## use .encrypt() instead of .decrypt() for this reason\n    xblk = aes.encrypt(iv)\n\n    ## decrypt and unshufflee to get our result\n    res = unshuffle(xor(xblk, blk))\n\n    stdout.buffer.write(res)\n"
  }
]