SQLCipher的使用

SQLCipher 是用来加密数据库

一. 

1.安装sqlcipher命令,首先需要安装brew,   在终端输入  

ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

成功之后在终端在运行 

brew install sqlcipher

二.

1. 创建加密数据库
$ sqlcipher encrypted.db
SQLCipher version 3.8.4.3 2014-04-03 16:53:12
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> PRAGMA key = 'thisiskey';
sqlite> create table encrypted (id integer, name text);
sqlite> .schema
CREATE TABLE encrypted (id integer, name text);
sqlite> .q


2. 打开加密数据库
$ sqlcipher encrypted.db
SQLCipher version 3.8.4.3 2014-04-03 16:53:12
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> PRAGMA key = 'thisiskey';
sqlite> .schema
CREATE TABLE encrypted (id integer, name text);


3. 修改数据库密码


 sqlite> PRAGMA rekey = 'newkey';


 4. 加密已有的数据库
 $ sqlcipher banklist.sqlite3 
SQLCipher version 3.8.4.3 2014-04-03 16:53:12
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> ATTACH DATABASE 'encrypted.db' AS encrypted KEY 'thisiskey';
sqlite> SELECT sqlcipher_export('encrypted');
sqlite> DETACH DATABASE encrypted;


5. 解密数据库
$ sqlcipher encrypted.db 
SQLCipher version 3.8.4.3 2014-04-03 16:53:12
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> PRAGMA key = 'thisiskey';
sqlite> ATTACH DATABASE 'plaintext.db' AS plaintext KEY '';
sqlite> SELECT sqlcipher_export('plaintext');
sqlite> DETACH DATABASE plaintext;

 转自 ： http://my.oschina.net/kjpioo/blog/149290

satckoverflow.com上有人提到过在

sqlite> sqlcipher-shell32.exe  test.db

sqlite> PRAGMA KEY = '12345';

给刚打开的数据库设置密码后，马上接着往数据库执行create table和 insert操作。最后用

sqlite> .e

退出该数据库。但是下次再用

sqlite> sqlcipher-shell32.exe  test.db

登录，在输入密码前执行了.schema等其他操作

sqlite>.schema

Error: file is encrypted or is not a database

sqlite> PRAGMA KEY = '12345';

Error: file is encrypted or is not a database

遭到提示：Error: file is encrypted or is not a database

根据官方以上英文描述，这个问题就是因为操作上没有遵循just-in-time key derivation的要求，没有首先输密码解密再进行其他操作。

有图为证：

----------------以下为正确操作过程：

SQLite version 3.7.15.2 2013-01-09 11:53:05
Enter ".help" for instructions
Enter SQL statements terminated with a ";"
sqlite> PRAGMA KEY = '12345';
sqlite> .schema
CREATE TABLE t(name text);
sqlite> select * from t;
n1
sqlite>

----------------以下为错误操作过程：

Enter SQL statements terminated with a ";"
sqlite> .schema
Error: file is encrypted or is not a database
sqlite> PRAGMA KEY = '12345';
sqlite> .schema
Error: file is encrypted or is not a database
sqlite>

确实如此。

以上过程你可以自己亲自验证以下。

注意：通过命令行（ sqlcipher-shell32.exe） 执行命令，与通过sqlite3 api调用操作sqlite3数据库，是一样的道理

参考：

https://www.zetetic.net/sqlcipher/sqlcipher-api/#key

PRAGMA key 

The process of creating a new, encrypted database is called “keying” the database. SQLCipher uses just-in-time key derivation at the point it is first needed for an operation. This means that the key (and any options) must be set before the first operation on the database. As soon as the database is touched (e.g. SELECT, CREATE TABLE, UPDATE, etc.) and pages need to be read or written, the key is prepared for use.

Example 1: Passphrase with Key Derivation

The key itself can be a passphrase, which is converted to a key using PBKDF2 key derivation. The result is used as the encryption key for the database.

sqlite> PRAGMA key = 'passphrase';

Example 2: Raw Key Data (Without Key Derivation)

Alternatively, it is possible to specify an exact byte sequence using a blob literal. With this method, it is the calling application's responsibility to ensure that the data provided is a 64 character hex string, which will be converted directly to 32 bytes (256 bits) of key data.

sqlite> PRAGMA key = "x'2DD29CA851E7B56E4697B0E1F08507293D761A05CE4D1B628663F411A8086D99'";

Testing the Key

When opening an existing database, PRAGMA key will not immediately throw an error if the key provided is incorrect. To test that the database can be successfully opened with the provided key, it is necessary to perform some operation on the database (i.e. read from it) and confirm it is success.

The easiest way to do this is select off the sqlite_master table, which will attempt to read the first page of the database and will parse the schema.

sqlite> PRAGMA key = 'passphrase';
sqlite> SELECT count(*) FROM sqlite_master; -- if this throws an error, the key was incorrect. If it succeeds and returns a numeric value, the key is correct;

The same check can be implemented in C code

sqlite3_key(database, "test123", 7);
if (sqlite3_exec(database, "SELECT count(*) FROM sqlite_master;", NULL, NULL, NULL) == SQLITE_OK) {
  // key is correct.
} else {
  // key is incorrect
}

Implementation Notes

• PRAGMA key should generally be called as the first operation on a database.