scrambleBytes.cpp

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/*
    A C++ program to parse DJI's ".txt" log files (recorded by the "DJI Go 4" app).
    Version 2021-05-20

    Copyright (c) 2021 Live Networks, Inc.  All rights reserved.
    For the latest version of this program (and more information), visit http://djilogs.live555.com

    Get an array of 8 bytes that were used to scramble (i.e., obfuscate) record data.
    Implementation.
*/

#include "scrambleBytes.hh"

static u_int64_t crc64Table[256] = {0x0,
0x7AD870C830358979, 0xF5B0E190606B12F2, 0x8F689158505E9B8B,
0xC038E5739841B68F, 0xBAE095BBA8743FF6, 0x358804E3F82AA47D,
0x4F50742BC81F2D04, 0xAB28ECB46814FE75, 0xD1F09C7C5821770C,
0x5E980D24087FEC87, 0x24407DEC384A65FE, 0x6B1009C7F05548FA,
0x11C8790FC060C183, 0x9EA0E857903E5A08, 0xE478989FA00BD371,
0x7D08FF3B88BE6F81, 0x7D08FF3B88BE6F8, 0x88B81EABE8D57D73,
0xF2606E63D8E0F40A, 0xBD301A4810FFD90E, 0xC7E86A8020CA5077,
0x4880FBD87094CBFC, 0x32588B1040A14285, 0xD620138FE0AA91F4,
0xACF86347D09F188D, 0x2390F21F80C18306, 0x594882D7B0F40A7F,
0x1618F6FC78EB277B, 0x6CC0863448DEAE02, 0xE3A8176C18803589,
0x997067A428B5BCF0, 0xFA11FE77117CDF02, 0x80C98EBF2149567B,
0xFA11FE77117CDF0, 0x75796F2F41224489, 0x3A291B04893D698D,
0x40F16BCCB908E0F4, 0xCF99FA94E9567B7F, 0xB5418A5CD963F206,
0x513912C379682177, 0x2BE1620B495DA80E, 0xA489F35319033385,
0xDE51839B2936BAFC, 0x9101F7B0E12997F8, 0xEBD98778D11C1E81,
0x64B116208142850A, 0x1E6966E8B1770C73, 0x8719014C99C2B083,
0xFDC17184A9F739FA, 0x72A9E0DCF9A9A271, 0x8719014C99C2B08,
0x4721E43F0183060C, 0x3DF994F731B68F75, 0xB29105AF61E814FE,
0xC849756751DD9D87, 0x2C31EDF8F1D64EF6, 0x56E99D30C1E3C78F,
0xD9810C6891BD5C04, 0xA3597CA0A188D57D, 0xEC09088B6997F879,
0x96D1784359A27100, 0x19B9E91B09FCEA8B, 0x636199D339C963F2,
0xDF7ADABD7A6E2D6F, 0xA5A2AA754A5BA416, 0x2ACA3B2D1A053F9D,
0x50124BE52A30B6E4, 0x1F423FCEE22F9BE0, 0x659A4F06D21A1299,
0xEAF2DE5E82448912, 0x902AAE96B271006B, 0x74523609127AD31A,
0xE8A46C1224F5A63, 0x81E2D7997211C1E8, 0xFB3AA75142244891,
0xB46AD37A8A3B6595, 0xCEB2A3B2BA0EECEC, 0x41DA32EAEA507767,
0x3B024222DA65FE1E, 0xA2722586F2D042EE, 0xD8AA554EC2E5CB97,
0x57C2C41692BB501C, 0x2D1AB4DEA28ED965, 0x624AC0F56A91F461,
0x1892B03D5AA47D18, 0x97FA21650AFAE693, 0xED2251AD3ACF6FEA,
0x95AC9329AC4BC9B, 0x7382B9FAAAF135E2, 0xFCEA28A2FAAFAE69,
0x8632586ACA9A2710, 0xC9622C4102850A14, 0xB3BA5C8932B0836D,
0x3CD2CDD162EE18E6, 0x460ABD1952DB919F, 0x256B24CA6B12F26D,
0x5FB354025B277B14, 0xD0DBC55A0B79E09F, 0xAA03B5923B4C69E6,
0xE553C1B9F35344E2, 0x9F8BB171C366CD9B, 0x10E3202993385610,
0x6A3B50E1A30DDF69, 0x8E43C87E03060C18, 0xF49BB8B633338561,
0x7BF329EE636D1EEA, 0x12B592653589793, 0x4E7B2D0D9B47BA97,
0x34A35DC5AB7233EE, 0xBBCBCC9DFB2CA865, 0xC113BC55CB19211C,
0x5863DBF1E3AC9DEC, 0x22BBAB39D3991495, 0xADD33A6183C78F1E,
0xD70B4AA9B3F20667, 0x985B3E827BED2B63, 0xE2834E4A4BD8A21A,
0x6DEBDF121B863991, 0x1733AFDA2BB3B0E8, 0xF34B37458BB86399,
0x8993478DBB8DEAE0, 0x6FBD6D5EBD3716B, 0x7C23A61DDBE6F812,
0x3373D23613F9D516, 0x49ABA2FE23CC5C6F, 0xC6C333A67392C7E4,
0xBC1B436E43A74E9D, 0x95AC9329AC4BC9B5, 0xEF74E3E19C7E40CC,
0x601C72B9CC20DB47, 0x1AC40271FC15523E, 0x5594765A340A7F3A,
0x2F4C0692043FF643, 0xA02497CA54616DC8, 0xDAFCE7026454E4B1,
0x3E847F9DC45F37C0, 0x445C0F55F46ABEB9, 0xCB349E0DA4342532,
0xB1ECEEC59401AC4B, 0xFEBC9AEE5C1E814F, 0x8464EA266C2B0836,
0xB0C7B7E3C7593BD, 0x71D40BB60C401AC4, 0xE8A46C1224F5A634,
0x927C1CDA14C02F4D, 0x1D148D82449EB4C6, 0x67CCFD4A74AB3DBF,
0x289C8961BCB410BB, 0x5244F9A98C8199C2, 0xDD2C68F1DCDF0249,
0xA7F41839ECEA8B30, 0x438C80A64CE15841, 0x3954F06E7CD4D138,
0xB63C61362C8A4AB3, 0xCCE411FE1CBFC3CA, 0x83B465D5D4A0EECE,
0xF96C151DE49567B7, 0x76048445B4CBFC3C, 0xCDCF48D84FE7545,
0x6FBD6D5EBD3716B7, 0x15651D968D029FCE, 0x9A0D8CCEDD5C0445,
0xE0D5FC06ED698D3C, 0xAF85882D2576A038, 0xD55DF8E515432941,
0x5A3569BD451DB2CA, 0x20ED197575283BB3, 0xC49581EAD523E8C2,
0xBE4DF122E51661BB, 0x3125607AB548FA30, 0x4BFD10B2857D7349,
0x4AD64994D625E4D, 0x7E7514517D57D734, 0xF11D85092D094CBF,
0x8BC5F5C11D3CC5C6, 0x12B5926535897936, 0x686DE2AD05BCF04F,
0xE70573F555E26BC4, 0x9DDD033D65D7E2BD, 0xD28D7716ADC8CFB9,
0xA85507DE9DFD46C0, 0x273D9686CDA3DD4B, 0x5DE5E64EFD965432,
0xB99D7ED15D9D8743, 0xC3450E196DA80E3A, 0x4C2D9F413DF695B1,
0x36F5EF890DC31CC8, 0x79A59BA2C5DC31CC, 0x37DEB6AF5E9B8B5,
0x8C157A32A5B7233E, 0xF6CD0AFA9582AA47, 0x4AD64994D625E4DA,
0x300E395CE6106DA3, 0xBF66A804B64EF628, 0xC5BED8CC867B7F51,
0x8AEEACE74E645255, 0xF036DC2F7E51DB2C, 0x7F5E4D772E0F40A7,
0x5863DBF1E3AC9DE, 0xE1FEA520BE311AAF, 0x9B26D5E88E0493D6,
0x144E44B0DE5A085D, 0x6E963478EE6F8124, 0x21C640532670AC20,
0x5B1E309B16452559, 0xD476A1C3461BBED2, 0xAEAED10B762E37AB,
0x37DEB6AF5E9B8B5B, 0x4D06C6676EAE0222, 0xC26E573F3EF099A9,
0xB8B627F70EC510D0, 0xF7E653DCC6DA3DD4, 0x8D3E2314F6EFB4AD,
0x256B24CA6B12F26, 0x788EC2849684A65F, 0x9CF65A1B368F752E,
0xE62E2AD306BAFC57, 0x6946BB8B56E467DC, 0x139ECB4366D1EEA5,
0x5CCEBF68AECEC3A1, 0x2616CFA09EFB4AD8, 0xA97E5EF8CEA5D153,
0xD3A62E30FE90582A, 0xB0C7B7E3C7593BD8, 0xCA1FC72BF76CB2A1,
0x45775673A732292A, 0x3FAF26BB9707A053, 0x70FF52905F188D57,
0xA2722586F2D042E, 0x854FB3003F739FA5, 0xFF97C3C80F4616DC,
0x1BEF5B57AF4DC5AD, 0x61372B9F9F784CD4, 0xEE5FBAC7CF26D75F,
0x9487CA0FFF135E26, 0xDBD7BE24370C7322, 0xA10FCEEC0739FA5B,
0x2E675FB4576761D0, 0x54BF2F7C6752E8A9, 0xCDCF48D84FE75459,
0xB71738107FD2DD20, 0x387FA9482F8C46AB, 0x42A7D9801FB9CFD2,
0xDF7ADABD7A6E2D6, 0x772FDD63E7936BAF, 0xF8474C3BB7CDF024,
0x829F3CF387F8795D, 0x66E7A46C27F3AA2C, 0x1C3FD4A417C62355,
0x935745FC4798B8DE, 0xE98F353477AD31A7, 0xA6DF411FBFB21CA3,
0xDC0731D78F8795DA, 0x536FA08FDFD90E51, 0x29B7D047EFEC8728
};

static u_int64_t crc64(u_int8_t seed, u_int8_t const* buffer, unsigned bufferSize) {
  u_int64_t crc = seed;

  for (unsigned i = 0; i < bufferSize; ++i) {
    u_int8_t tabIndex = buffer[i] ^ crc;
    crc = crc64Table[tabIndex] ^ (crc >> 8);
  }

  return crc;
}

void getScrambleBytes(u_int8_t recordType, u_int8_t keyByte,
                      u_int8_t* resultScrambleBytes) {
  // Set up the (8-byte) buffer to compute the CRC over:
  u_int64_t dataForBuffer = 0x123456789ABCDEF0*keyByte;
  u_int8_t bufferToCRC[8];
  // Fill in the buffer in little-endian order:
  for (unsigned i = 0; i < sizeof bufferToCRC; ++i) {
    bufferToCRC[i] = dataForBuffer; // low 8 bits
    dataForBuffer >>= 8;
  }

  // Compute a CRC over this buffer, using our "recordType" and "keyByte" parameters as salt:
  u_int64_t crcResult = crc64(recordType + keyByte, bufferToCRC, sizeof bufferToCRC);

  // Unpack this into "resultScrambleBytes", in little-endian order:
  for (unsigned i = 0; i < 8; ++i) {
    resultScrambleBytes[i] = crcResult; // low 8 bits
    crcResult >>= 8;
  }
}