DBMS_CRYPTO package

DBMS_CRYPTO provides an interface to encrypt and decrypt stored data, and can be used in conjunction with PL/SQL programs running network communications. It provides support for several industry-standard encryption and hashing algorithms, including the Advanced Encryption Standard (AES) encryption algorithm. AES has been approved by the National Institute of Standards and Technology (NIST) to replace the Data Encryption Standard (DES).

 

See Also: Oracle Database Security Guide for further information about using this package and about encrypting data in general.

DBMS_CRYPTO contains basic cryptographic functions and procedures. To use this package correctly and securely, a general level of security expertise is assumed.

The DBMS_CRYPTO package enables encryption and decryption for common Oracle datatypes, including RAW and large objects (LOBs), such as images and sound. Specifically, it supports BLOBs and CLOBs. In addition, it provides Globalization Support for encrypting data across different database character sets.

The following cryptographic algorithms are supported:

·         Data Encryption Standard (DES), Triple DES (3DES, 2-key and 3-key)

·         Advanced Encryption Standard (AES)

·         MD5, MD4, and SHA-1 cryptographic hashes

·         MD5 and SHA-1 Message Authentication Code (MAC)

Block cipher modifiers are also provided with DBMS_CRYPTO. You can choose from several padding options, including PKCS (Public Key Cryptographic Standard) #5, and from four block cipher chaining modes, including Cipher Block Chaining (CBC).

Package Feature	DBMS_CRYPTO	DBMS_OBFUSCATION_TOOLKIT
Cryptographic algorithms	DES, 3DES, AES, RC4, 3DES_2KEY	DES, 3DES
Padding forms	PKCS5, zeroes	none supported
Block cipher chaining modes	CBC, CFB, ECB, OFB	CBC
Cryptographic hash algorithms	MD5, SHA-1, MD4	MD5
Keyed hash (MAC) algorithms	HMAC_MD5, HMAC_SH1	none supported
Cryptographic pseudo-random number generator	RAW, NUMBER, BINARY_INTEGER	RAW, VARCHAR2
Database types	RAW, CLOB, BLOB	RAW, VARCHAR2

DBMS_CRYPTO is intended to replace the DBMS_OBFUSCATION_TOOLKIT, providing greater ease of use and support for a range of algorithms to accommodate new and existing systems. Specifically, 3DES_2KEY and MD4 are provided for backward compatibility. It is not recommended that you use these algorithms because they do not provide the same level of security as provided by 3DES, AES, MD5, or SHA-1.

Parameters for the DBMS_CRYPTO subprograms use these datatypes:

Type	Description
BLOB	A source or destination binary LOB
CLOB	A source or destination character LOB (excluding NCLOB)
PLS_INTEGER	Specifies a cryptographic algorithm type (used with BLOB, CLOB, and RAW datatypes)
RAW	A source or destination RAW buffer

The following cryptographic algorithms, modifiers, and cipher suites are predefined in this package.

Name	Description
HASH_MD4	Produces a 128-bit hash, or message digest of the input message
HASH_MD5	Also produces a 128-bit hash, but is more complex than MD4
HASH_SH1	Secure Hash Algorithm (SHA). Produces a 160-bit hash.

DBMS_CRYPTO Encryption Algorithms:

Name	Description
ENCRYPT_DES	Data Encryption Standard. Block cipher. Uses key length of 56 bits.
ENCRYPT_3DES_2KEY	Data Encryption Standard. Block cipher. Operates on a block 3 times with 2 keys. Effective key length of 112 bits.
ENCRYPT_3DES	Data Encryption Standard. Block cipher. Operates on a block 3 times.
ENCRYPT_AES128	Advanced Encryption Standard. Block cipher. Uses 128-bit key size.
ENCRYPT_AES192	Advanced Encryption Standard. Block cipher. Uses 192-bit key size.
ENCRYPT_AES256	Advanced Encryption Standard. Block cipher. Uses 256-bit key size.
ENCRYPT_RC4	Stream cipher. Uses a secret, randomly generated key unique to each session.

When to Use Encrypt and Decrypt Procedures or Functions

This package includes both ENCRYPT and DECRYPT procedures and functions. The procedures are used to encrypt or decrypt LOB datatypes (overloaded for CLOB and BLOB datatypes). In contrast, the ENCRYPT and DECRYPT functions are used to encrypt and decrypt RAW datatypes. Data of type VARCHAR2 must be converted to RAW before you can use DBMS_CRYPTO functions to encrypt it.

When to Use Hash or Message Authentication Code (MAC) Functions

This package includes two different types of one-way hash functions: the HASH function and the MAC function. Hash functions operate on an arbitrary-length input message, and return a fixed-length hash value. One-way hash functions work in one direction only. It is easy to compute a hash value from an input message, but it is extremely difficult to generate an input message that hashes to a particular value. Note that hash values should be at least 128 bits in length to be considered secure.

You can use hash values to verify whether data has been altered. For example, before storing data, Laurel runs DBMS_CRYPTO.HASH against the stored data to create a hash value. When she retrieves the stored data at a later date, she can again run the hash function against it, using the same algorithm. If the second hash value is identical to the first one, then the data has not been altered. Hash values are similar to "file fingerprints" and are used to ensure data integrity.

The HASH function included with DBMS_CRYPTO, is a one-way hash function that you can use to generate a hash value from either RAW or LOB data. The MAC function is also a one-way hash function, but with the addition of a secret key. It works the same way as the DBMS_CRYPTO.HASH function, except only someone with the key can verify the hash value.

MACs can be used to authenticate files between users. They can also be used by a single user to determine if her files have been altered, perhaps by a virus. A user could compute the MAC of his files and store that value in a table. If the user did not use a MAC function, then the virus could compute the new hash value after infection and replace the table entry. A virus cannot do that with a MAC because the virus does not know the key.

About Generating and Storing Encryption Keys

The DBMS_CRYPTO package can generate random material for encryption keys, but it does not provide a mechanism for maintaining them. Application developers must take care to ensure that the encryption keys used with this package are securely generated and stored. Also note that the encryption and decryption operations performed by DBMS_CRYPTO occur on the server, not on the client. Consequently, if the key is sent over the connection between the client and the server, the connection must be protected by using network encryption. Otherwise, the key is vulnerable to capture over the wire.

Although DBMS_CRYPTO cannot generate keys on its own, it does provide tools you can use to aid in key generation. For example, you can use the RANDOMBYTES function to generate random material for keys. (Calls to the RANDOMBYTES function behave like calls to the DESGETKEY and DES3GETKEY functions of the DBMS_OBFUSCATION_TOOLKIT package.)

When generating encryption keys for DES, it is important to remember that some numbers are considered weak and semi-weak keys. Keys are considered weak or semi-weak when the pattern of the algorithm combines with the pattern of the initial key value to produce ciphertext that is more susceptible to cryptanalysis. To avoid this, filter out the known weak DES keys. Lists of the known weak and semi-weak DES keys are available on several public Internet sites.

 

Conversion Rules

To convert VARCHAR2 to RAW, use the UTL_I18N.STRING_TO_RAW function to perform the following steps:

1.       Convert VARCHAR2 in the current database character set to VARCHAR2 in the AL32UTF8 database character.

2.       Convert VARCHAR2 in the AL32UTF8 database character set to RAW.

Syntax example: UTL_I18N.STRING_TO_RAW (string, 'AL32UTF8');
To convert RAW to VARCHAR2, use the UTL_I18N.RAW_TO_CHAR function to perform the following steps:

1.       Convert RAW to VARCHAR2 in the AL32UTF8 database character set.

2.       Convert VARCHAR2 in the AL32UTF8 database character set to VARCHAR2 in the database character set you wish to use.

Syntax example: UTL_I18N.RAW_TO_CHAR (data, 'AL32UTF8');

Example: The following listing shows PL/SQL block encrypting and decrypting pre-defined 'input_string' using 256-bit AES algorithm with Cipher Block Chaining and PKCS#5 compliant padding.

DECLARE  
   input_string    VARCHAR2 (200):= 'Secret Message';  
   output_string   VARCHAR2 (200);  
   encrypted_raw   RAW (2000);       -- stores encrypted binary text  
   decrypted_raw   RAW (2000);       -- stores decrypted binary text  
   num_key_bytes   NUMBER := 256/8;    -- key length 256 bits (32 bytes)  
   key_bytes_raw   RAW (32);        -- stores 256-bit encryption key  
   encryption_type  PLS_INTEGER :=     -- total encryption type  
               DBMS_CRYPTO.ENCRYPT_AES256  
              + DBMS_CRYPTO.CHAIN_CBC  
              + DBMS_CRYPTO.PAD_PKCS5;  
 BEGIN  
   DBMS_OUTPUT.PUT_LINE ( 'Original string: ' || input_string);  
   key_bytes_raw := DBMS_CRYPTO.RANDOMBYTES (num_key_bytes);  
   encrypted_raw := DBMS_CRYPTO.ENCRYPT  
    (  
      src => UTL_I18N.STRING_TO_RAW (input_string, 'AL32UTF8'),  
      typ => encryption_type,  
      key => key_bytes_raw  
    );  
   -- The encrypted value "encrypted_raw" can be used here  
   decrypted_raw := DBMS_CRYPTO.DECRYPT  
    (  
      src => encrypted_raw,  
      typ => encryption_type,  
      key => key_bytes_raw  
    );  
   output_string := UTL_I18N.RAW_TO_CHAR (decrypted_raw, 'AL32UTF8');  
   DBMS_OUTPUT.PUT_LINE ('Decrypted string: ' || output_string);  
 END;