sqlcipher/src/crypto.c

/* 
** SQLCipher
** crypto.c developed by Stephen Lombardo (Zetetic LLC) 
** sjlombardo at zetetic dot net
** http://zetetic.net
** 
** Copyright (c) 2009, ZETETIC LLC
** All rights reserved.
** 
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are met:
**     * Redistributions of source code must retain the above copyright
**       notice, this list of conditions and the following disclaimer.
**     * Redistributions in binary form must reproduce the above copyright
**       notice, this list of conditions and the following disclaimer in the
**       documentation and/or other materials provided with the distribution.
**     * Neither the name of the ZETETIC LLC nor the
**       names of its contributors may be used to endorse or promote products
**       derived from this software without specific prior written permission.
** 
** THIS SOFTWARE IS PROVIDED BY ZETETIC LLC ''AS IS'' AND ANY
** EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
** WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
** DISCLAIMED. IN NO EVENT SHALL ZETETIC LLC BE LIABLE FOR ANY
** DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
** (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
** ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
** SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
**  
*/
/* BEGIN CRYPTO */
#ifdef SQLITE_HAS_CODEC

#include <assert.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/hmac.h>
#include "sqliteInt.h"
#include "btreeInt.h"
#include "crypto.h"


#ifndef OMIT_MEMLOCK
#if defined(__unix__) || defined(__APPLE__) 
#include <sys/mman.h>
#elif defined(_WIN32)
# include <windows.h>
#endif
#endif


#ifdef CODEC_DEBUG
#define CODEC_TRACE(X)  {printf X;fflush(stdout);}
#else
#define CODEC_TRACE(X)
#endif

void sqlite3FreeCodecArg(void *pCodecArg);

typedef struct {
  int derive_key;
  EVP_CIPHER *evp_cipher;
  int kdf_iter;
  int key_sz;
  int iv_sz;
  int pass_sz;
  unsigned char *key;
  char *pass;
} cipher_ctx;

typedef struct {
  int kdf_salt_sz;
  int mode_rekey;
  unsigned char *kdf_salt;
  unsigned char *buffer;
  Btree *pBt;
  cipher_ctx *read_ctx;
  cipher_ctx *write_ctx;
} codec_ctx;

static void activate_openssl() {
  sqlite3_mutex_enter(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
  if(EVP_get_cipherbyname(CIPHER) == NULL) {
    OpenSSL_add_all_algorithms();
  } 
  sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
}

/*
**  Simple routines for converting hex char strings to binary data
 */
static int cipher_hex2int(char c) {
  return (c>='0' && c<='9') ? (c)-'0' :
         (c>='A' && c<='F') ? (c)-'A'+10 :
         (c>='a' && c<='f') ? (c)-'a'+10 : 0;
}

static void cipher_hex2bin(const char *hex, int sz, unsigned char *out){
  int i;
  for(i = 0; i < sz; i += 2){
    out[i/2] = (cipher_hex2int(hex[i])<<4) | cipher_hex2int(hex[i+1]);
  }
}


/**
  * Free and wipe memory
  * If ptr is not null memory will be freed. 
  * If sz is greater than zero, the memory will be overwritten with zero before it is freed
  */
static void codec_free(void *ptr, int sz) {
  if(ptr) {
    if(sz > 0) {
      memset(ptr, 0, sz);
#ifndef OMIT_MEMLOCK
#if defined(__unix__) || defined(__APPLE__) 
      munlock(ptr, sz);
#elif defined(_WIN32)
      VirtualUnlock(ptr, sz);
#endif
#endif
    }
    sqlite3_free(ptr);
  }
}

/**
  * allocate memory. Uses sqlite's internall malloc wrapper so memory can be 
  * reference counted and leak detection works. Unless compiled with OMIT_MEMLOCK
  * attempts to lock the memory pages so sensitive information won't be swapped
  */
void* codec_malloc(int sz) {
  void *ptr = sqlite3Malloc(sz);
#ifndef OMIT_MEMLOCK
  if(ptr) {
#if defined(__unix__) || defined(__APPLE__) 
    mlock(ptr, sz);
#elif defined(_WIN32)
    VirtualLock(ptr, sz);
#endif
  }
#endif
  return ptr;
}


/**
  * Set the raw password / key data for a cipher context
  * 
  * returns SQLITE_OK if assignment was successfull
  * returns SQLITE_NOMEM if an error occured allocating memory
  * returns SQLITE_ERROR if the key couldn't be set because the pass was null or size was zero
  */
static int cipher_ctx_set_pass(cipher_ctx *ctx, const void *zKey, int nKey) {
  codec_free(ctx->pass, ctx->pass_sz);
  ctx->pass_sz = nKey;
  if(zKey && nKey) {
    ctx->pass = codec_malloc(nKey);
    if(ctx->pass == NULL) return SQLITE_NOMEM;
    memcpy(ctx->pass, zKey, nKey);
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
}

/**
  * Initialize a a new cipher_ctx struct. This function will allocate memory
  * for the cipher context and for the key
  * 
  * returns SQLITE_OK if initialization was successful
  * returns SQLITE_NOMEM if an error occured allocating memory
  */
static int cipher_ctx_init(cipher_ctx **iCtx) {
  cipher_ctx *ctx;
  *iCtx = codec_malloc(sizeof(cipher_ctx));
  ctx = *iCtx;
  if(ctx == NULL) return SQLITE_NOMEM;
  memset(ctx, 0, sizeof(cipher_ctx)); 
  ctx->key = codec_malloc(EVP_MAX_KEY_LENGTH);
  if(ctx->key == NULL) return SQLITE_NOMEM;
  return SQLITE_OK;
}

/**
  * Free and wipe memory associated with a cipher_ctx
  */
static void cipher_ctx_free(cipher_ctx **iCtx) {
  cipher_ctx *ctx = *iCtx;
  CODEC_TRACE(("cipher_ctx_free: entered iCtx=%d\n", iCtx));
  codec_free(ctx->key, ctx->key_sz);
  codec_free(ctx->pass, ctx->pass_sz);
  codec_free(ctx, sizeof(cipher_ctx)); 
}

/**
  * Copy one cipher_ctx to another. For instance, assuming that read_ctx is a 
  * fully initialized context, you could copy it to write_ctx and all yet data
  * and pass information across
  *
  * returns SQLITE_OK if initialization was successful
  * returns SQLITE_NOMEM if an error occured allocating memory
  */
static int cipher_ctx_copy(cipher_ctx *target, cipher_ctx *source) {
  void *key = target->key; 
  CODEC_TRACE(("cipher_ctx_copy: entered target=%d, source=%d\n", target, source));
  codec_free(target->pass, target->pass_sz); 
  memcpy(target, source, sizeof(cipher_ctx));
  
  target->key = key; //restore pointer to previously allocated key data
  memcpy(target->key, source->key, EVP_MAX_KEY_LENGTH);
  target->pass = codec_malloc(source->pass_sz);
  if(target->pass == NULL) return SQLITE_NOMEM;
  memcpy(target->pass, source->pass, source->pass_sz);
  return SQLITE_OK;
}

/**
  * Compare one cipher_ctx to another.
  *
  * returns 0 if all the parameters (except the derived key data) are the same
  * returns 1 otherwise
  */
static int cipher_ctx_cmp(cipher_ctx *c1, cipher_ctx *c2) {
  CODEC_TRACE(("cipher_ctx_cmp: entered c1=%d c2=%d\n", c1, c2));

  if(
    c1->evp_cipher == c2->evp_cipher
    && c1->iv_sz == c2->iv_sz
    && c1->kdf_iter == c2->kdf_iter
    && c1->key_sz == c2->key_sz
    && c1->pass_sz == c2->pass_sz
    && (
      c1->pass == c2->pass
      || !memcmp(c1->pass, c2->pass, c1->pass_sz)
    ) 
  ) return 0;
  return 1;
}

/**
  * Free and wipe memory associated with a cipher_ctx, including the allocated
  * read_ctx and write_ctx.
  */
static void codec_ctx_free(codec_ctx **iCtx) {
  codec_ctx *ctx = *iCtx;
  CODEC_TRACE(("codec_ctx_free: entered iCtx=%d\n", iCtx));
  codec_free(ctx->kdf_salt, ctx->kdf_salt_sz);
  codec_free(ctx->buffer, 0);
  cipher_ctx_free(&ctx->read_ctx);
  cipher_ctx_free(&ctx->write_ctx);
  codec_free(ctx, sizeof(codec_ctx)); 
}

/**
  * Derive an encryption key for a cipher contex key based on the raw password.
  *
  * If the raw key data is formated as x'hex' and there are exactly enough hex chars to fill
  * the key space (i.e 64 hex chars for a 256 bit key) then the key data will be used directly. 
  * 
  * Otherwise, a key data will be derived using PBKDF2
  * 
  * returns SQLITE_OK if initialization was successful
  * returns SQLITE_NOMEM if the key could't be derived (for instance if pass is NULL or pass_sz is 0)
  */
static int codec_key_derive(codec_ctx *ctx, cipher_ctx *c_ctx) { 
  CODEC_TRACE(("codec_key_derive: entered c_ctx->pass=%s, c_ctx->pass_sz=%d ctx->kdf_salt=%d ctx->kdf_salt_sz=%d c_ctx->kdf_iter=%d c_ctx->key_sz=%d\n", 
    c_ctx->pass, c_ctx->pass_sz, ctx->kdf_salt, ctx->kdf_salt_sz, c_ctx->kdf_iter, c_ctx->key_sz));

  if(c_ctx->pass && c_ctx->pass_sz) { // if pass is not null
    if (c_ctx->pass_sz == ((c_ctx->key_sz*2)+3) && sqlite3StrNICmp(c_ctx->pass ,"x'", 2) == 0) { 
      int n = c_ctx->pass_sz - 3; /* adjust for leading x' and tailing ' */
      const char *z = c_ctx->pass + 2; /* adjust lead offset of x' */ 
      CODEC_TRACE(("codec_key_derive: deriving key from hex\n")); 
      cipher_hex2bin(z, n, c_ctx->key);
    } else { 
      CODEC_TRACE(("codec_key_derive: deriving key using PBKDF2\n")); 
      PKCS5_PBKDF2_HMAC_SHA1(c_ctx->pass, c_ctx->pass_sz, ctx->kdf_salt, ctx->kdf_salt_sz, c_ctx->kdf_iter, c_ctx->key_sz, c_ctx->key);
    }
    return SQLITE_OK;
  };
  return SQLITE_ERROR;
}

/*
 * ctx - codec context
 * pgno - page number in database
 * size - size in bytes of input and output buffers
 * mode - 1 to encrypt, 0 to decrypt
 * in - pointer to input bytes
 * out - pouter to output bytes
 */
static int codec_cipher(cipher_ctx *ctx, Pgno pgno, int mode, int size, unsigned char *in, unsigned char *out) {
  EVP_CIPHER_CTX ectx;
  unsigned char *iv;
  int tmp_csz, csz;

  CODEC_TRACE(("codec_cipher:entered pgno=%d, mode=%d, size=%d\n", pgno, mode, size));

  /* just copy raw data from in to out when key size is 0
   * i.e. during a rekey of a plaintext database */ 
  if(ctx->key_sz == 0) {
    memcpy(out, in, size);
    return SQLITE_OK;
  } 

  // FIXME - only run if using an IV
  size = size - ctx->iv_sz; /* adjust size to useable size and memset reserve at end of page */
  iv = out + size;
  if(mode == CIPHER_ENCRYPT) {
    RAND_bytes(iv, ctx->iv_sz);
  } else {
    memcpy(iv, in+size, ctx->iv_sz);
  } 
  
  EVP_CipherInit(&ectx, ctx->evp_cipher, NULL, NULL, mode);
  EVP_CIPHER_CTX_set_padding(&ectx, 0);
  EVP_CipherInit(&ectx, NULL, ctx->key, iv, mode);
  EVP_CipherUpdate(&ectx, out, &tmp_csz, in, size);
  csz = tmp_csz;  
  out += tmp_csz;
  EVP_CipherFinal(&ectx, out, &tmp_csz);
  csz += tmp_csz;
  EVP_CIPHER_CTX_cleanup(&ectx);
  assert(size == csz);

  return SQLITE_OK;
}

int codec_set_kdf_iter(sqlite3* db, int nDb, int kdf_iter, int for_ctx) {
  struct Db *pDb = &db->aDb[nDb];
  CODEC_TRACE(("codec_set_kdf_iter: entered db=%d nDb=%d kdf_iter=%d for_ctx=%d\n", db, nDb, kdf_iter, for_ctx));

  if(pDb->pBt) {
    codec_ctx *ctx;
    cipher_ctx *c_ctx;
    sqlite3pager_get_codec(pDb->pBt->pBt->pPager, (void **) &ctx);
    c_ctx = for_ctx ? ctx->write_ctx : ctx->read_ctx;

    c_ctx->kdf_iter = kdf_iter;
    c_ctx->derive_key = 1;

    if(for_ctx == 2) cipher_ctx_copy( for_ctx ? ctx->read_ctx : ctx->write_ctx, c_ctx); 
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
}

/**
  * 
  * when for_ctx == 0 then it will change for read
  * when for_ctx == 1 then it will change for write
  * when for_ctx == 2 then it will change for both
  */
int codec_set_cipher_name(sqlite3* db, int nDb, const char *cipher_name, int for_ctx) {
  struct Db *pDb = &db->aDb[nDb];
  CODEC_TRACE(("codec_set_cipher_name: entered db=%d nDb=%d cipher_name=%s for_ctx=%d\n", db, nDb, cipher_name, for_ctx));

  if(pDb->pBt) {
    codec_ctx *ctx;
    cipher_ctx *c_ctx;
    sqlite3pager_get_codec(pDb->pBt->pBt->pPager, (void **) &ctx);
    c_ctx = for_ctx ? ctx->write_ctx : ctx->read_ctx;

    c_ctx->evp_cipher = (EVP_CIPHER *) EVP_get_cipherbyname(cipher_name);
    c_ctx->key_sz = EVP_CIPHER_key_length(c_ctx->evp_cipher);
    c_ctx->iv_sz = EVP_CIPHER_iv_length(c_ctx->evp_cipher);
    c_ctx->derive_key = 1;

    if(for_ctx == 2) cipher_ctx_copy( for_ctx ? ctx->read_ctx : ctx->write_ctx, c_ctx); 
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
}

int codec_set_pass_key(sqlite3* db, int nDb, const void *zKey, int nKey, int for_ctx) {
  struct Db *pDb = &db->aDb[nDb];
  CODEC_TRACE(("codec_set_pass_key: entered db=%d nDb=%d cipher_name=%s nKey=%d for_ctx=%d\n", db, nDb, zKey, nKey, for_ctx));
  if(pDb->pBt) {
    codec_ctx *ctx;
    cipher_ctx *c_ctx;
    sqlite3pager_get_codec(pDb->pBt->pBt->pPager, (void **) &ctx);
    c_ctx = for_ctx ? ctx->write_ctx : ctx->read_ctx;
  
    cipher_ctx_set_pass(c_ctx, zKey, nKey);
    c_ctx->derive_key = 1;

    if(for_ctx == 2) cipher_ctx_copy( for_ctx ? ctx->read_ctx : ctx->write_ctx, c_ctx); 
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
} 

/*
 * sqlite3Codec can be called in multiple modes.
 * encrypt mode - expected to return a pointer to the 
 *   encrypted data without altering pData.
 * decrypt mode - expected to return a pointer to pData, with
 *   the data decrypted in the input buffer
 */
void* sqlite3Codec(void *iCtx, void *data, Pgno pgno, int mode) {
  codec_ctx *ctx = (codec_ctx *) iCtx;
  int pg_sz = SQLITE_DEFAULT_PAGE_SIZE;
  int offset = 0;
  unsigned char *pData = (unsigned char *) data;
 
  CODEC_TRACE(("sqlite3Codec: entered pgno=%d, mode=%d, ctx->mode_rekey=%d, pg_sz=%d\n", pgno, mode, ctx->mode_rekey, pg_sz));

  /* derive key on first use if necessary */
  if(ctx->read_ctx->derive_key) {
    codec_key_derive(ctx, ctx->read_ctx);
    ctx->read_ctx->derive_key = 0;
  }

  if(ctx->write_ctx->derive_key) {
    if(cipher_ctx_cmp(ctx->write_ctx, ctx->read_ctx) == 0) {
      cipher_ctx_copy(ctx->write_ctx, ctx->read_ctx); // the relevant parameters are the same, just copy read key
    } else {
      codec_key_derive(ctx, ctx->write_ctx);
      ctx->write_ctx->derive_key = 0;
    }
  }


  if(pgno == 1) offset = FILE_HEADER_SZ; /* adjust starting pointers in data page for header offset on first page*/

  CODEC_TRACE(("sqlite3Codec: switch mode=%d offset=%d\n",  mode, offset));
  switch(mode) {
    case 0: /* decrypt */
    case 2:
    case 3:
      if(pgno == 1) memcpy(ctx->buffer, SQLITE_FILE_HEADER, FILE_HEADER_SZ); /* copy file header to the first 16 bytes of the page */ 
      codec_cipher(ctx->read_ctx, pgno, CIPHER_DECRYPT, pg_sz - offset, pData + offset, ctx->buffer + offset);
      memcpy(pData, ctx->buffer, pg_sz); /* copy buffer data back to pData and return */
      return pData;
      break;
    case 6: /* encrypt */
      if(pgno == 1) memcpy(ctx->buffer, ctx->kdf_salt, FILE_HEADER_SZ); /* copy salt to output buffer */ 
      codec_cipher(ctx->write_ctx, pgno, CIPHER_ENCRYPT, pg_sz - offset, pData + offset, ctx->buffer + offset);
      return ctx->buffer; /* return persistent buffer data, pData remains intact */
      break;
    case 7:
      if(pgno == 1) memcpy(ctx->buffer, ctx->kdf_salt, FILE_HEADER_SZ); /* copy salt to output buffer */ 
      codec_cipher(ctx->read_ctx, pgno, CIPHER_ENCRYPT, pg_sz - offset, pData + offset, ctx->buffer + offset);
      return ctx->buffer; /* return persistent buffer data, pData remains intact */
      break;
    default:
      return pData;
      break;
  }
}


int sqlite3CodecAttach(sqlite3* db, int nDb, const void *zKey, int nKey) {
  struct Db *pDb = &db->aDb[nDb];

  CODEC_TRACE(("sqlite3CodecAttach: entered nDb=%d zKey=%s, nKey=%d\n", nDb, zKey, nKey));
  activate_openssl();
  
  if(nKey && zKey && pDb->pBt) {
    codec_ctx *ctx;
    int rc;
    Pager *pPager = pDb->pBt->pBt->pPager;
    sqlite3_file *fd;

    ctx = codec_malloc(sizeof(codec_ctx));
    if(ctx == NULL) return SQLITE_NOMEM;
    memset(ctx, 0, sizeof(codec_ctx)); /* initialize all pointers and values to 0 */

    ctx->pBt = pDb->pBt; /* assign pointer to database btree structure */

    if((rc = cipher_ctx_init(&ctx->read_ctx)) != SQLITE_OK) return rc; 
    if((rc = cipher_ctx_init(&ctx->write_ctx)) != SQLITE_OK) return rc; 
    
    /* pre-allocate a page buffer of PageSize bytes. This will
       be used as a persistent buffer for encryption and decryption 
       operations to avoid overhead of multiple memory allocations*/
    ctx->buffer = codec_malloc(SQLITE_DEFAULT_PAGE_SIZE);
    if(ctx->buffer == NULL) return SQLITE_NOMEM;
     
    /* allocate space for salt data. Then read the first 16 bytes 
       directly off the database file. This is the salt for the
       key derivation function. If we get a short read allocate
       a new random salt value */
    ctx->kdf_salt_sz = FILE_HEADER_SZ;
    ctx->kdf_salt = codec_malloc(ctx->kdf_salt_sz);
    if(ctx->kdf_salt == NULL) return SQLITE_NOMEM;


    fd = sqlite3Pager_get_fd(pPager);
    if(fd == NULL || sqlite3OsRead(fd, ctx->kdf_salt, FILE_HEADER_SZ, 0) != SQLITE_OK) {
      /* if unable to read the bytes, generate random salt */
      RAND_bytes(ctx->kdf_salt, FILE_HEADER_SZ);
    }

    sqlite3pager_sqlite3PagerSetCodec(sqlite3BtreePager(pDb->pBt), sqlite3Codec, NULL, sqlite3FreeCodecArg, (void *) ctx);

    codec_set_cipher_name(db, nDb, CIPHER, 0);
    codec_set_kdf_iter(db, nDb, PBKDF2_ITER, 0);
    codec_set_pass_key(db, nDb, zKey, nKey, 0);
    cipher_ctx_copy(ctx->write_ctx, ctx->read_ctx);

    sqlite3_mutex_enter(db->mutex);
    
    /* Always overwrite page size and set to the default because the first page of the database
       in encrypted and thus sqlite can't effectively determine the pagesize. this causes an issue in 
       cases where bytes 16 & 17 of the page header are a power of 2 as reported by John Lehman

       Note: before forcing the page size we need to force pageSizeFixed to 0, else  
             sqliteBtreeSetPageSize will block the change 
    */
    pDb->pBt->pBt->pageSizeFixed = 0; 
    sqlite3BtreeSetPageSize(ctx->pBt, SQLITE_DEFAULT_PAGE_SIZE, EVP_MAX_IV_LENGTH, 0);

    /* if fd is null, then this is an in-memory database and
       we dont' want to overwrite the AutoVacuum settings
       if not null, then set to the default */
    if(fd != NULL) { 
      sqlite3BtreeSetAutoVacuum(ctx->pBt, SQLITE_DEFAULT_AUTOVACUUM);
    }

    sqlite3_mutex_leave(db->mutex);
  }
  return SQLITE_OK;
}

void sqlite3FreeCodecArg(void *pCodecArg) {
  codec_ctx *ctx = (codec_ctx *) pCodecArg;
  if(pCodecArg == NULL) return;
  codec_ctx_free(&ctx); // wipe and free allocated memory for the context 
}

void sqlite3_activate_see(const char* in) {
  /* do nothing, security enhancements are always active */
}

int sqlite3_key(sqlite3 *db, const void *pKey, int nKey) {
  CODEC_TRACE(("sqlite3_key: entered db=%d pKey=%s nKey=%d\n", db, pKey, nKey));
  /* attach key if db and pKey are not null and nKey is > 0 */
  if(db && pKey && nKey) {
    sqlite3CodecAttach(db, 0, pKey, nKey); // operate only on the main db 
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
}

/* sqlite3_rekey 
** Given a database, this will reencrypt the database using a new key.
** There are two possible modes of operation. The first is rekeying
** an existing database that was not previously encrypted. The second
** is to change the key on an existing database.
** 
** The proposed logic for this function follows:
** 1. Determine if there is already a key present
** 2. If there is NOT already a key present, create one and attach a codec (key would be null)
** 3. Initialize a ctx->rekey parameter of the codec
** 
** Note: this will require modifications to the sqlite3Codec to support rekey
**
*/
int sqlite3_rekey(sqlite3 *db, const void *pKey, int nKey) {
  CODEC_TRACE(("sqlite3_rekey: entered db=%d pKey=%s, nKey=%d\n", db, pKey, nKey));
  activate_openssl();
  if(db && pKey && nKey) {
    struct Db *pDb = &db->aDb[0];
    CODEC_TRACE(("sqlite3_rekey: database pDb=%d\n", pDb));
    if(pDb->pBt) {
      codec_ctx *ctx;
      int rc, page_count;
      Pgno pgno;
      PgHdr *page;
      Pager *pPager = pDb->pBt->pBt->pPager;

      sqlite3pager_get_codec(pDb->pBt->pBt->pPager, (void **) &ctx);
     
      if(ctx == NULL) { 
        CODEC_TRACE(("sqlite3_rekey: no codec attached to db, attaching now\n"));
        /* there was no codec attached to this database,so attach one now with a null password */
        sqlite3CodecAttach(db, 0, pKey, nKey);
        sqlite3pager_get_codec(pDb->pBt->pBt->pPager, (void **) &ctx);
        
        /* prepare this setup as if it had already been initialized */
        RAND_bytes(ctx->kdf_salt, ctx->kdf_salt_sz);
        ctx->read_ctx->key_sz = ctx->read_ctx->iv_sz =  ctx->read_ctx->pass_sz = 0;
      }

      sqlite3_mutex_enter(db->mutex);

      if(ctx->read_ctx->iv_sz != ctx->write_ctx->iv_sz) {
        char *error;
        CODEC_TRACE(("sqlite3_rekey: updating page size for iv_sz change from %d to %d\n", ctx->read_ctx->iv_sz, ctx->write_ctx->iv_sz));
        db->nextPagesize = SQLITE_DEFAULT_PAGE_SIZE;
        pDb->pBt->pBt->pageSizeFixed = 0; /* required for sqlite3BtreeSetPageSize to modify pagesize setting */
        sqlite3BtreeSetPageSize(pDb->pBt, db->nextPagesize, EVP_MAX_IV_LENGTH, 0);
        sqlite3RunVacuum(&error, db);
      }

      codec_set_pass_key(db, 0, pKey, nKey, 1);
      ctx->mode_rekey = 1; 
    
      /* do stuff here to rewrite the database 
      ** 1. Create a transaction on the database
      ** 2. Iterate through each page, reading it and then writing it.
      ** 3. If that goes ok then commit and put ctx->rekey into ctx->key
      **    note: don't deallocate rekey since it may be used in a subsequent iteration 
      */
      rc = sqlite3BtreeBeginTrans(pDb->pBt, 1); /* begin write transaction */
      sqlite3PagerPagecount(pPager, &page_count);
      for(pgno = 1; rc == SQLITE_OK && pgno <= page_count; pgno++) { /* pgno's start at 1 see pager.c:pagerAcquire */
        if(!sqlite3pager_is_mj_pgno(pPager, pgno)) { /* skip this page (see pager.c:pagerAcquire for reasoning) */
          rc = sqlite3PagerGet(pPager, pgno, &page);
          if(rc == SQLITE_OK) { /* write page see pager_incr_changecounter for example */
            rc = sqlite3PagerWrite(page);
            //printf("sqlite3PagerWrite(%d)\n", pgno);
            if(rc == SQLITE_OK) {
              sqlite3PagerUnref(page);
            } 
          } 
        } 
      }

      /* if commit was successful commit and copy the rekey data to current key, else rollback to release locks */
      if(rc == SQLITE_OK) { 
        CODEC_TRACE(("sqlite3_rekey: committing\n"));
        db->nextPagesize = SQLITE_DEFAULT_PAGE_SIZE;
        rc = sqlite3BtreeCommit(pDb->pBt); 
        cipher_ctx_copy(ctx->read_ctx, ctx->write_ctx);
      } else {
        CODEC_TRACE(("sqlite3_rekey: rollback\n"));
        sqlite3BtreeRollback(pDb->pBt);
      }

      ctx->mode_rekey = 0;
      sqlite3_mutex_leave(db->mutex);
    }
    return SQLITE_OK;
  }
  return SQLITE_ERROR;
}

void sqlite3CodecGetKey(sqlite3* db, int nDb, void **zKey, int *nKey) {
  struct Db *pDb = &db->aDb[nDb];
  CODEC_TRACE(("sqlite3CodecGetKey: entered db=%d, nDb=%d\n", db, nDb));
  
  if( pDb->pBt ) {
    codec_ctx *ctx;
    sqlite3pager_get_codec(pDb->pBt->pBt->pPager, (void **) &ctx);

    if(ctx) { /* if the codec has an attached codec_context user the raw key data */
      *zKey = ctx->read_ctx->pass;
      *nKey = ctx->read_ctx->pass_sz;
    } else {
      *zKey = NULL;
      *nKey = 0;
    }
  }
}


/* END CRYPTO */
#endif