Difference between revisions of "Securing Your Data"

Latest revision as of 12:12, 26 January 2010

Securing Your Data

Controlling Access to Data

The most basic level of database security is provided by the operating system. Recital tables and indexes are individual files with their own respective operating system file permissions. Read permission is required to open a table and write permission to update a table. If a user does not have read permission they are denied access. Without write permission, a table will be opened read-only.

Here the owner, root, and members of the recital group have write permission, so can update the example table unless additional protection applies. Other users can open the example table read-only.

# ls -l example*
-rwxrwxr-x    1 root     recital        147 Nov 29 14:27 example.dbd
-rwxrwxr-x    1 root     recital     41580 Nov 29 14:27 example.dbf
-rwxrwxr-x    1 root     recital     13312 Nov 29 14:28 example.dbt
-rwxrwxr-x    1 root     recital     19456 Nov 29 14:28 example.dbx

Note: As in the example above, a table's associated files should have the same permissions as the table itself:

Security

Operating System permissions can be further refined, while still using the Operating System user and group IDs, in the Security and Protection sections of the Dictionary. The Security section handles table based operations and the Protection section focuses on individual fields.

Security and Protection rules can be defined using the grant and revoke statements and are based on Access Control Strings. An Access Control String (ACS) is a range of valid user identification codes, and is used to restrict table operations to certain individuals or groups. A user identification code is the combination of group and user numbers. When constructing an Access Control String of linked user identification codes, wild card characters may be used.

The maximum ACS length is 254 characters.

Access Control Strings may be associated with the following operations:

// Grant insert privilege for the customer table
open database southwind
grant insert on customers to "[20,100]" 
 
// Grant all privileges to all users
open database southwind
grant all on shippers to public

Protection

Like Security rules, Protection rules can be defined using the grant and revoke statements and are based on Access Control Strings.

// Grant update privilege for columns lastname and firstname from the customer table
open database southwind
grant update (lastname, firstname) on customers TO "[20,100]"

Protecting Data with Constraints

Column Constraints

The Dictionary column constraints either prevent the entry of incorrect data, e.g. must_enter and validation or aid the entry of correct data, e.g. default, picture and choicelist.

The column constraints are as follows:

These can be specified in create table or alter table statements:

Example

open database southwind
alter table customers;
  add column timeref char(8);
  check validtime(timeref);
  error "Not a valid time string"

Table Constraints

Table Constraints allow event-driven procedures to be called before an I/O operation. These can be used to introduce another layer of checks before a particular operation is permitted to take place or to simply set up logging of that operation.

The following table constraints may be applied in the create table and alter table statements:

Examples

open database southwind
alter table customers modify onupdate "p_update"
alter table customers modify ondelete "p_delete"
alter table customers modify oninsert "p_insert"
alter table customers modify onopen "p_open"
alter table customers modify onclose "p_close"
alter table customers modify onrollback "p_rollback"

The check constraint and its associated error constraint can also be defined at table level.

Examples

open database southwind
alter table customers add check callauth(); 
  error "Not authorized"

DES3 Encrypting Your Data

Recital gives you the ability to encrypt the data held in Recital tables. Once a table has been encrypted, the data cannot be accessed unless the correct three-part encryption key is specified, providing additional security for sensitive data.

• encrypt

encrypt <tablename as character> | <skeleton as character> key <key as character>

The encrypt command is used to encrypt the data in the specified table or tables matching a skeleton. If the skeleton syntax is used, then all matching tables will be given the same encryption key. The encryption key is a three part comma-separated key and may optionally be enclosed in angled brackets. Each part of the key can be a maximum of 8 characters. The key is DES3 encrypted and stored in a .dkf file with the same basename as the table. After encryption, the three parts of the key must be specified correctly before the table can be accessed.

// Encrypt individual tables
encrypt customers key "key_1,key_2,key_3"
encrypt employees key "<key_1,key_2,key_3>"
 
// Encrypt all .dbf files in the directory
encrypt *.dbf key "key_1,key_2,key_3"

• set encryption

set encryption to [<key as character>]
set encryption on | off

If a database table is encrypted, the correct three-part encryption key must be specified before the table's data or structure can be accessed. The set encryption to set command can be used to specify a default encryption key to be used whenever an encrypted table is accessed without the key being specified. The encryption key is a three part comma-separated key.

If the command to access the table includes the key, either by appending it to the table filename specification or using an explicit clause, this will take precedence over the key defined by set encryption to. Issuing set encryption to without a key causes any previous setting to be cleared. The key must then be specified for each individual encrypted table.

The default key defined by set encryption to is only active when set encryption is on. Set encryption off can be used to temporarily disable the default key. The set encryption on | off setting does not change the default key itself. Set encryption is on by default.

// Encrypt individual tables
encrypt customers key "key_1,key_2,key_3"
encrypt shippers key "key_2,key_3,key_4"
// Specify a default encryption key
set encryption to "key_1,key_2,key_3"
// Open customers table using the default encryption key
use customers
// Specify shippers table's encryption key
use shippers<key_2,key_3,key_4>
// Disable the default encryption key
set encryption to
// Specify the individual encryption keys
use customers encryption "key_1,key_2,key_3"
use shippers<key_2,key_3,key_4>

• decrypt

encrypt <tablename as character> | <skeleton as character> key <key as character>

The decrypt command is used to decrypt the data in the specified table or tables matching a skeleton. The specified key must contain the three part comma-separated key used to previously encrypt the table and may optionally be enclosed in angled brackets. The skeleton syntax can only be used if all tables matching the skeleton have the same key.

The decrypt command decrypts the data and removes the table's '.dkf file. After decryption, the key need no longer be specified to gain access to the table.

// Decrypt individual tables
decrypt customers key "key_1,key_2,key_3"
decrypt employees key "<key_1,key_2,key_3>"
 
// Decrypt all .dbf files in the directory
decrypt *.dbf key "key_1,key_2,key_3"

All of the following commands are affected when a table is encrypted:

• append from - append records to the active table from another table

// The key must be specified for an encrypted source table
use mycustomers
append from customers encryption "key_1,key_2,key_3";
for country = "UK"

• copy file - copy a file

// The key file must also be copied for an encrypted source table
// as the target table will be encrypted
encrypt customers key "key_1,key_2,key_3"
copy file customers.dbf to newcustomers.dbf
copy file customers.dkf to newcustomers.dkf
use newcustomers encryption "key_1,key_2,key_3"

• copy structure - copy a table's structure to a new table

// The key file is automatically copied for an encrypted source table
// and the target table encrypted
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3"
copy structure to blankcust
use blankcust encryption "key_1,key_2,key_3"

• copy - copy a table

// By default, the key file is automatically copied for an encrypted
// source table and the target table encrypted with the same key
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3"
copy to newcustomers
use newcustomers encryption "key_1,key_2,key_3"
// You can also create a copy with a different key
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3"
copy to newcustomers encrypt "newkey_1,newkey_2,newkey_3"
use newcustomers encryption "newkey_1,newkey_2,newkey_3"
// Or create a decrypted copy
encrypt customers key "key_1,key_2,key_3";
use customers encryption "key_1,key_2,key_3"
copy to newcustomers decrypt
use newcustomers
// You can also create an encrypted copy of a non-encrypted source table
use orders
copy to encorders encrypt "newkey_1,newkey_2,newkey_3"
use encorders encryption "newkey_1,newkey_2,newkey_3"

• dir - display a directory listing of tables

// Encrypted tables are flagged as such with (DES3)
open database southwind
dir

Current database: southwind
Tables		# Records		Last Update	Size		Dictionary	Triggers	Security
categories.dbf		8		01/10/09		24576	None		None		None
cisamdemo.dbf	--->	CISAM/Bridge	[cisamdemo]
customers.dbf (DES3)	91		05/12/09		49600	None		None		None
employees.dbf		9		05/12/09		25520	None		None		None
example.dbf   (DES3)	100		12/24/09		38080	Yes		Yes		None
order_details.dbf		2155		05/12/09		296320	None		None		None
orders.dbf			829		05/12/09		232704  	None		None		None
products.dbf		77		05/12/09		37112  	None		None		None
productsbyname.dbf	77		05/12/09		29104  	None		None		None
shippers.dbf  (DES3)	3		05/12/09		20864  	None		None		None
suppliers.dbf		29		12/08/09		29992  	Yes		None		None

   0.765 MB in 11 files.
   1.093 GB remaining on drive.

• use - open a table

// The three part key must be specified to open an
// encrypted table.  All of the following are valid.
// 1. Specifying a default encryption key before opening the table
set encryption to "key_1,key_2,key_3"
use customers
// 2. Appending the key to the filename
use customers<key_1,key_2,key_3>
// 3. Using the ENCRYPTION clause, optionally specifying angled brackets
use customers encryption "key_1,key_2,key_3"
use customers encryption "<key_1,key_2,key_3>"

• SQL insert - add a row to a table

// The three part key can be specified using a
// default encryption key before opening the table
open database southwind
set encryption to "key_1,key_2,key_3"
insert into customers;
  (customerid, companyname);
  values ("RECIT","Recital Corporation")
// Or by appending the key to the filename
open database southwind
insert into customers<key_1,key_2,key_3>;
  (customerid, companyname);
  values ("RECIT","Recital Corporation")

• SQL select - return data from a table or tables

// The three part key can be specified using a
// default encryption key before opening the table
open database southwind
set encryption to "key_1,key_2,key_3"
select * from customers
// Or by appending the key to the filename
open database southwind
select * from customers<key_1,key_2,key_3>

• SQL update - update data in a table

// The three part key can be specified using a
// default encryption key before opening the table
open database southwind
set encryption to "key_1,key_2,key_3"
update customers;
  set companyname="Recital Corporation Inc.";
  where customerid="RECIT"
// Or by appending the key to the filename
open database southwind
update customers<key_1,key_2,key_3>;
  set companyname="Recital Corporation Inc.";
  where customerid="RECIT"