Decoder-ECM.cpp

#include <string.h>
#include "Global.h"
#include "Decoder.h"
#include "Crypto.h"
#include "Keyset.h"

typedef struct
{
  // 0x00
  u8 ProtocolNumber;
  // 0x01
  u8 BroadcasterGroupID;
  // 0x02
  u8 WorkKeyID;
  // 0x03
  u8 ScramblingKeyOdd[8];
  // 0x0b
  u8 ScramblingKeyEven[8];
  // 0x13
  u8 ProgramType;
  // 0x14
  u8 Date[2];
  // 0x16
  u8 Time[3];
  // 0x19
  u8 RecordingControl;
} ECM_t;

typedef u8 CRC32_t[4];
typedef u8 MAC_t[4];

static s32
DecryptECM (const ECM_t * ECM, u32 Size, u8 * Output, u8 * Key)
{
  if (ECM == NULL || Size < sizeof (ECM_t) + sizeof (MAC_t))
    return -1;

  //BCAS::Keyset::GetKey (ECM->BroadcasterGroupID, ECM->WorkKeyID, Key);
  s32 rc = BCAS::Keyset::GetKey (ECM->BroadcasterGroupID, ECM->WorkKeyID, Key);
  if (rc < 0)
    return rc;

  *Output++ = ECM->ProtocolNumber;
  *Output++ = ECM->BroadcasterGroupID;
  *Output++ = ECM->WorkKeyID;

  BCAS::Crypto::Transform (ECM->ProtocolNumber, Key, ECM->ScramblingKeyOdd,
			   Size - 3, Output, true);

  return 0;
}

s32
BCAS::Decoder::DecodeECM (const u8 * Payload, u32 Size, u8 * Keys, u8 * Nanos)
{
  u8
    Plaintext[256];
  u8
    Key[8];
  u8
    MAC[4];

  if (Payload == NULL || Size < sizeof (ECM_t) + sizeof (MAC_t))
    return -1;

  const ECM_t *
    ECM = reinterpret_cast < const
    ECM_t * >(Payload);

  if (DecryptECM (ECM, Size, Plaintext, Key) < 0)
    {
      if (Keys != NULL)
	memset (Keys, 0, 16);

      return -2;
    }

  Size -= sizeof (MAC_t);
  BCAS::Crypto::GenerateMAC (ECM->ProtocolNumber, Key, Plaintext, Size, MAC);
  if (memcmp (MAC, Plaintext + Size, sizeof (MAC_t)))
    return -3;

  ECM = reinterpret_cast < const ECM_t *>(Plaintext);

  if (Keys != NULL)
    memcpy (Keys, ECM->ScramblingKeyOdd, 16);
  if (Nanos != NULL)
    memcpy (Nanos, ECM + 1, Size - sizeof (ECM_t));

  return 0;
}