System.Data.SQLite

#ifdef SQLITE_HAS_CODEC
  void sqlite3pager_free_codecarg(void *pArg);
#endif

#include "src/pager.c"

#ifndef SQLITE_OMIT_DISKIO
#ifdef SQLITE_HAS_CODEC

#include <windows.h>
#include <wincrypt.h>

// Extra padding before and after the cryptographic buffer
#define CRYPT_OFFSET 8

typedef struct _CRYPTBLOCK
{
  HCRYPTKEY hReadKey;     // Key used to read from the database and write to the journal
  HCRYPTKEY hWriteKey;    // Key used to write to the database
  DWORD     dwPageSize;   // Size of pages
  LPVOID    pvCrypt;      // A buffer for encrypting/decrypting (if necessary)

  // Existing cryptblocks may have a buffer, if so, delete it
  if (pBlock->pvCrypt)
  {
    sqliteFree(pBlock->pvCrypt);
    pBlock->pvCrypt = NULL;
  }

  // Figure out how big to make our spare crypt block

  if (CryptEncrypt(hKey, 0, TRUE, 0, NULL, &pBlock->dwCryptSize, pBlock->dwCryptSize * 2))
  {


    pBlock->pvCrypt = sqliteMalloc(pBlock->dwCryptSize + (CRYPT_OFFSET * 2));

  }
  return pBlock;
}

// Destroy a cryptographic context and any buffers and keys allocated therein
static void DestroyCryptBlock(LPCRYPTBLOCK pBlock)
{

  }

  // All done with this cryptblock
  sqliteFree(pBlock);
}

// Encrypt/Decrypt functionality, called by pager.c
void * sqlite3Codec(void *pArg, void *data, Pgno nPageNum, int nMode)
{
  LPCRYPTBLOCK pBlock = (LPCRYPTBLOCK)pArg;
  DWORD dwPageSize;
  LPVOID pvTemp;

  if (!pBlock) return data;

  // Make sure the page size for the pager is still the same as the page size
  // for the cryptblock.  If the user changed it, we need to adjust!
  if (nMode != 2)
  {
    PgHdr *pageHeader;
    pageHeader = DATA_TO_PGHDR(data);
    if (pageHeader->pPager->pageSize != pBlock->dwPageSize)
    {
      // Update the cryptblock to reflect the new page size
      CreateCryptBlock(0, pageHeader->pPager, pBlock);
    }
  }














  switch(nMode)
  {
  case 0: // Undo a "case 7" journal file encryption
  case 2: // Reload a page
  case 3: // Load a page
    if (!pBlock->hReadKey) break;

    /* Block ciphers often need to write extra padding beyond the 
    data block.  We don't have that luxury for a given page of data so
    we must copy the page data to a buffer that IS large enough to hold
    the padding.  We then encrypt the block and write the buffer back to
    the page without the unnecessary padding.
    We only use the special block of memory if its absolutely necessary. */
    if (pBlock->dwCryptSize != pBlock->dwPageSize)
    {
      CopyMemory(((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET, data, pBlock->dwPageSize);
      pvTemp = data;
      data = ((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET;
    }


    dwPageSize = pBlock->dwCryptSize;
    CryptDecrypt(pBlock->hReadKey, 0, TRUE, 0, (LPBYTE)data, &dwPageSize);

    // If the encryption algorithm required extra padding and we were forced to encrypt or
    // decrypt a copy of the page data to a temp buffer, then write the contents of the temp
    // buffer back to the page data minus any padding applied.
    if (pBlock->dwCryptSize != pBlock->dwPageSize)
    {
      CopyMemory(pvTemp, data, pBlock->dwPageSize);
      data = pvTemp;
    }
    break;
  case 6: // Encrypt a page for the main database file
    if (!pBlock->hWriteKey) break;

    CopyMemory(((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET, data, pBlock->dwPageSize);
    data = ((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET;

    dwPageSize = pBlock->dwPageSize;
    CryptEncrypt(pBlock->hWriteKey, 0, TRUE, 0, ((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET, &dwPageSize, pBlock->dwCryptSize);
    break;
  case 7: // Encrypt a page for the journal file
    /* Under normal circumstances, the readkey is the same as the writekey.  However,
    when the database is being rekeyed, the readkey is not the same as the writekey.
    The rollback journal must be written using the original key for the
    database file because it is, by nature, a rollback journal.
    Therefore, for case 7, when the rollback is being written, always encrypt using
    the database's readkey, which is guaranteed to be the same key that was used to
    read the original data.
    */
    if (!pBlock->hReadKey) break;

    CopyMemory(((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET, data, pBlock->dwPageSize);
    data = ((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET;

    dwPageSize = pBlock->dwPageSize;
    CryptEncrypt(pBlock->hReadKey, 0, TRUE, 0, ((LPBYTE)pBlock->pvCrypt) + CRYPT_OFFSET, &dwPageSize, pBlock->dwCryptSize);
    break;
  }






  return data;

}

// Derive an encryption key from a user-supplied buffer
static HCRYPTKEY DeriveKey(const void *pKey, int nKeyLen)
{
  HCRYPTHASH hHash = 0;
  HCRYPTKEY  hKey;