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Oracle® Database Security Guide
11g Release 1 (11.1)

Part Number B28531-01
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9 Developing Applications Using the Data Encryption API

This chapter describes how Oracle Database manages data encryption by using the DBMS_CRYPTO and DBMS_SQLHASH PL/SQL packages. It contains the following topics:

See Also:

9.1 Securing Sensitive Information

While the Internet poses new challenges in information security, many of them can be addressed by traditional security mechanisms:

Encryption is an important component of several of these solutions. For example, Secure Sockets Layer (SSL), an Internet-standard network encryption and authentication protocol, uses encryption to authenticate users by means of X.509 digital certificates. SSL also uses encryption to ensure data confidentiality, and cryptographic checksums to ensure data integrity. Many of these uses of encryption are relatively transparent to a user or application. For example, many browsers support SSL, and users generally do not need to do anything special to enable SSL encryption.

Oracle Database provided network encryption between database clients and the Oracle database since Oracle Database version 7 . Oracle Advanced Security, an option to Oracle Database, provides encryption and cryptographic checksums for integrity checking with any protocol supported by the database, including Oracle Net, Java Database Connectivity (JDBC—both thick and thin JDBC), and the Internet Intra-Orb Protocol (IIOP). Oracle Advanced Security also supports SSL for Oracle Net, thick JDBC, and IIOP connections.

Encryption is not a remedy for all security problems, but it is an important tool that addresses specific security threats. In particular, the rapid growth of e-business has spurred increased encryption of stored data, such as credit card numbers. While SSL is typically used to protect these numbers in transit to a Web site, where data is not protected as it is in storage, the file system or database storing them often does so as clear text (unencrypted). Information stored in the clear is then directly accessible to anyone who can break into the host and gain root access, or gain illicit access to the database.

Databases can be made secure through proper configuration, but they can also be vulnerable to host break-ins if the host is misconfigured. In well-publicized break-ins, an intruder obtained a large list of credit card numbers by breaking into a database. Had the data been encrypted, the stolen information would have been useless. Encrypting stored data is an important tool in limiting information loss in the rare occurrence that access controls are bypassed.

9.2 Security Problems That Encryption Does Not Solve

While there are many good reasons to encrypt data, there are many reasons not to encrypt data. Encryption does not solve all security problems, and may make some problems worse. The following sections describe some misconceptions about encryption of stored data:

9.2.1 Principle 1: Encryption Does Not Solve Access Control Problems

Most organizations need to limit data access to users who need to see this data. For example, a human resources system may limit employees to viewing only their own employment records, while allowing managers of employees to see the employment records of subordinates. Human resource specialists may also need to see employee records for multiple employees.

Typically, you can use access control mechanisms to address security policies that limit data access to those with a need to see it. Oracle Database has provided strong, independently evaluated access control mechanisms for many years. It enables access control enforcement to a fine level of granularity through Virtual Private Database.

Because human resource records are considered sensitive information, it is tempting to think that all information should be encrypted for better security. However, encryption cannot enforce granular access control, and it may hinder data access. For example, an employee, his manager, and a human resources clerk may all need to access an employee record. If all employee data is encrypted, then all three must be able to access the data in unencrypted form. Therefore, the employee, the manager and the human resources clerk would have to share the same encryption key to decrypt the data. Encryption would, therefore, not provide any additional security in the sense of better access control, and the encryption might hinder the proper or efficient functioning of the application. An additional issue is that it is difficult to securely transmit and share encryption keys among multiple users of a system.

A basic principle behind encrypting stored data is that it must not interfere with access control. For example, a user who has the SELECT privilege on emp should not be limited by the encryption mechanism from seeing all the data he is otherwise allowed to see. Similarly, there is little benefit to encrypting part of a table with one key and part of a table with another key if users need to see all encrypted data in the table. In this case, encryption adds to the overhead of decrypting the data before users can read it. If access controls are implemented well, then encryption adds little additional security within the database itself. A user who has privileges to access data within the database has no more nor any less privileges as a result of encryption. Therefore, you should never use encryption to solve access control problems.

9.2.2 Principle 2: Encryption Does Not Protect Against a Malicious Database Administrator

Some organizations, concerned that a malicious user might gain elevated (database administrator) privileges by guessing a password, like the idea of encrypting stored data to protect against this threat. However, the correct solution to this problem is to protect the database administrator account, and to change default passwords for other privileged accounts. The easiest way to break into a database is by using a default password for a privileged account that an administrator allowed to remain unchanged. One example is SYS/CHANGE_ON_INSTALL.

While there are many destructive things a malicious user can do to a database after gaining the DBA privilege, encryption will not protect against many of them. Examples include corrupting or deleting data, exporting user data to the file system to e-mail the data back to himself to run a password cracker on it, and so on.

Some organizations are concerned that database administrators, typically having all privileges, are able to see all data in the database. These organizations feel that the database administrators should administer the database, but should not be able to see the data that the database contains. Some organizations are also concerned about concentrating so much privilege in one person, and would prefer to partition the DBA function, or enforce two-person access rules.

It is tempting to think that encrypting all data (or significant amounts of data) will solve these problems, but there are better ways to protect against these threats. For example, Oracle Database supports limited partitioning of DBA privileges. Oracle Database provides native support for SYSDBA and SYSOPER users. SYSDBA has all privileges, but SYSOPER has a limited privilege set (such as startup and shutdown of the database).

Furthermore, you can create smaller roles encompassing a number of system privileges. A jr_dba role might not include all system privileges, but only those appropriate to a junior database administrator (such as CREATE TABLE, CREATE USER, and so on).

Oracle Database also enables auditing the actions taken by SYS (or SYS-privileged users) and storing that audit trail in a secure operating system location. Using this model, a separate auditor who has root privileges on the operating system can audit all actions by SYS, enabling the auditor to hold all database administrators accountable for their actions.

See "Auditing Administrative Users" for information about ways to audit database administrators.

You can also fine-tune the access and control that database administrators have by using Oracle Database Vault. See Oracle Database Vault Administrator's Guide for more information.

The database administrator function is a trusted position. Even organizations with the most sensitive data, such as intelligence agencies, do not typically partition the database administrator function. Instead, they manage their database administrators strongly, because it is a position of trust. Periodic auditing can help to uncover inappropriate activities.

Encryption of stored data must not interfere with the administration of the database, because otherwise, larger security issues can result. For example, if by encrypting data you corrupt the data, then you create a security problem, the data itself cannot be interpreted, and it may not be recoverable.

You can use encryption to limit the ability of a database administrator or other privileged user to see data in the database. However, it is not a substitute for managing the database administrator privileges properly, or for controlling the use of powerful system privileges. If untrustworthy users have significant privileges, then they can pose multiple threats to an organization, some of them far more significant than viewing unencrypted credit card numbers.

9.2.3 Principle 3: Encrypting Everything Does Not Make Data Secure

A common error is to think that if encrypting some data strengthens security, then encrypting everything makes all data secure.

As the discussion of the previous two principles illustrates, encryption does not address access control issues well, and it is important that encryption not interfere with normal access controls. Furthermore, encrypting an entire production database means that all data must be decrypted to be read, updated, or deleted. Encryption is inherently a performance-intensive operation; encrypting all data will significantly affect performance.

Availability is a key aspect of security. If encrypting data makes data unavailable, or adversely affects availability by reducing performance, then encrypting everything will create a new security problem. Availability is also adversely affected by the database being inaccessible when encryption keys are changed, as good security practices require on a regular basis. When the keys are to be changed, the database is inaccessible while data is decrypted and reencrypted with a new key or keys.

There may be advantages to encrypting data stored off-line. For example, an organization may store backups for a period of 6 months to a year off-line, in a remote location. Of course, the first line of protection is to secure the facility storing the data, by establishing physical access controls. Encrypting this data before it is stored may provide additional benefits. Because it is not being accessed on-line, performance need not be a consideration. While an Oracle database does not provide this capability, there are vendors who provide encryption services. Before embarking on large-scale encryption of backup data, organizations considering this approach should thoroughly test the process. It is essential to verify that data encrypted before off-line storage can be decrypted and re-imported successfully.

9.3 Data Encryption Challenges

In cases where encryption can provide additional security, there are some associated technical challenges, as described in the following sections:

9.3.1 Encrypting Indexed Data

Special difficulties arise when encrypted data is indexed. For example, suppose a company uses a national identity number, such as the U.S. social security number (SSN), as the employee number for its employees. The company considers employee numbers to be sensitive data, and, therefore, wants to encrypt data in the employee_number column of the employees table. Because employee_number contains unique values, the database designers want to have an index on it for better performance.

However, if DBMS_CRYPTO or the DBMS_OBFUSCATION_TOOLKIT (or another mechanism) is used to encrypt data in a column, then an index on that column will also contain encrypted values. Although an index can be used for equality checking (for example, SELECT * FROM emp WHERE employee_number = '1232456789'), if the index on that column contains encrypted values, then the index is essentially unusable for any other purpose. You should not encrypt indexed data.

Oracle recommends that you do not use national identity numbers as unique IDs. Instead, use the CREATE SEQUENCE statement to generate unique identity numbers. Reasons to avoid using national identity numbers are as follows:

  • There are privacy issues associated with overuse of national identity numbers (for example, identity theft).

  • Sometimes national identity numbers can have duplicates, as with U.S. social security numbers.

9.3.2 Generating Encryption Keys

Encrypted data is only as secure as the key used for encrypting it. An encryption key must be securely generated using secure cryptographic key generation. Oracle Database provides support for secure random number generation, with the RANDOMBYTES function of DBMS_CRYPTO. (This function replaces the capabilities provided by the GetKey procedure of the earlier DBMS_OBFUSCATION_TOOLKIT.) DBMS_CRYPTO calls the secure random number generator (RNG) previously certified by RSA Security.


Do not use the DBMS_RANDOM package. The DBMS_RANDOM package generates pseudo-random numbers, which, as Randomness Recommendations for Security (RFC-1750) states that using pseudo-random processes to generate secret quantities can result in pseudo-security.

Be sure to provide the correct number of bytes when you encrypt a key value. For example, you must provide a 16-byte key for the ENCRYPT_AES128 encryption algorithm.

9.3.3 Transmitting Encryption Keys

If the encryption key is to be passed by the application to the database, then you must encrypt it. Otherwise, an intruder could get access to the key as it is being transmitted. Network encryption, such as that provided by Oracle Advanced Security, protects all data in transit from modification or interception, including cryptographic keys.

9.3.4 Storing Encryption Keys

Storing encryption keys is one of the most important, yet difficult, aspects of encryption. To recover data encrypted with a symmetric key, the key must be accessible to an authorized application or user seeking to decrypt the data. At the same time, the key must be inaccessible to someone who is maliciously trying to access encrypted data that he is not supposed to see.

The options available to a developer are: Storing the Encryption Keys in the Database

Storing the keys in the database cannot always provide infallible security if you are trying to protect against the database administrator accessing encrypted data. An all-privileged database administrator could still access tables containing encryption keys. However, it can often provide good security against the casual curious user or against someone compromising the database file on the operating system.

As a trivial example, suppose you create a table (EMP) that contains employee data. You want to encrypt the employee social security number (SSN) stored in one of the columns. You could encrypt employee SSN using a key that is stored in a separate column. However, anyone with SELECT access on the entire table could retrieve the encryption key and decrypt the matching SSN.

While this encryption scheme seems easily defeated, with a little more effort you can create a solution that is much harder to break. For example, you could encrypt the SSN using a technique that performs some additional data transformation on the employee_number before using it to encrypt the SSN. This technique might be as simple as using an XOR operation on the employee_number and the birth date of the employee to determine the validity of the values.

As additional protection, PL/SQL source code performing encryption can be wrapped, (using the WRAP utility) which obfuscates (scrambles) the code. The WRAP utility processes an input SQL file and obfuscates the PL/SQL units in it. For example, the following command uses the keymanage.sql file as the input:

wrap iname=/mydir/keymanage.sql

A developer can subsequently have a function in the package call the DBMS_OBFUSCATION_TOOLKIT with the key contained in the wrapped package.

Oracle Database enables you to obfuscate dynamically generated PL/SQL code. The DBMS_DDL package contains two subprograms that allow you to obfuscate dynamically generated PL/SQL program units. For example, the following block uses the DBMS_DDL.CREATE_WRAPPED procedure to wrap dynamically generated PL/SQL code.


While wrapping is not unbreakable, it makes it harder for an intruder to get access to the encryption key. Even in cases where a different key is supplied for each encrypted data value, you should not embed the key value within a package. Instead, wrap the package that performs the key management (that is, data transformation or padding).

See Also:

Oracle Database PL/SQL Language Reference for additional information about the WRAP command line utility and the DBMS_DDL subprograms for dynamic wrapping

An alternative to wrapping the data is to have a separate table in which to store the encryption key and to envelope the call to the keys table with a procedure. The key table can be joined to the data table using a primary key to foreign key relationship. For example, employee_number is the primary key in the employees table that stores employee information and the encrypted SSN. The employee_number column is a foreign key to the ssn_keys table that stores the encryption keys for the employee SSN. The key stored in the ssn_keys table can also be transformed before use (by using an XOR operation), so the key itself is not stored unencrypted. If you wrap the procedure, then that can hide the way in which the keys are transformed before use.

The strengths of this approach are:

  • Users who have direct table access cannot see the sensitive data unencrypted, nor can they retrieve the keys to decrypt the data.

  • Access to decrypted data can be controlled through a procedure that selects the encrypted data, retrieves the decryption key from the key table, and transforms it before it can be used to decrypt the data.

  • The data transformation algorithm is hidden from casual snooping by wrapping the procedure, which obfuscates the procedure code.

  • SELECT access to both the data table and the keys table does not guarantee that the user with this access can decrypt the data, because the key is transformed before use.

The weakness to this approach is that a user who has SELECT access to both the key table and the data table, and who can derive the key transformation algorithm, can break the encryption scheme.

The preceding approach is not infallible, but it is adequate to protect against easy retrieval of sensitive information stored in clear text. Storing the Encryption Keys in the Operating System

Storing keys in a flat file in the operating system is another option. Oracle Database enables you to make callouts from PL/SQL, which you could use to retrieve encryption keys. However, if you store keys in the operating system and make callouts to it, then your data is only as secure as the protection on the operating system. If your primary security concern is that the database can be broken into from the operating system, then storing the keys in the operating system makes it easier for an intruder to retrieve encrypted data than storing the keys in the database itself. Users Managing Their Own Encryption Keys

Having the user supply the key assumes the user will be responsible with the key. Considering that 40 percent of help desk calls are from users who have forgotten their passwords, you can see the risks of having users manage encryption keys. In all likelihood, users will either forget an encryption key, or write the key down, which then creates a security weakness. If a user forgets an encryption key or leaves the company, then your data is not recoverable.

If you do decide to have user-supplied or user-managed keys, then you need to ensure you are using network encryption so that the key is not passed from the client to the server in the clear. You also must develop key archive mechanisms, which is also a difficult security problem. Key archives and backdoors create the security weaknesses that encryption is attempting to solve. Using Transparent Database Encryption and Tablespace Encryption

Transparent database encryption and tablespace encryption provide secure encryption with automatic key management for the encrypted tables and tablespaces. If the application requires protection of sensitive column data stored on the media, then these two types of encryption are a simple and fast way of achieving this.

See Also:

Oracle Database Advanced Security Administrator's Guide for more information about transparent data encryption

9.3.5 Changing Encryption Keys

Prudent security practice dictates that you periodically change encryption keys. For stored data, this requires periodically unencrypting the data, and reencrypting it with another well-chosen key. You would most likely change the encryption key while the data is not being accessed, which creates another challenge. This is especially true for a Web-based application encrypting credit card numbers, because you do not want to shut down the entire application while you switch encryption keys.

9.3.6 Encrypting Binary Large Objects

Certain data types require more work to encrypt. For example, Oracle Database supports storage of binary large objects (BLOBs), which stores very large objects (for example, multiple gigabytes) in the database. A BLOB can be either stored internally as a column, or stored in an external file.

For an example of using DBMS_CRYPTO on BLOB data, see Example of Encryption and Decryption Procedures for BLOB Data.

9.4 Storing Data Encryption by Using the DBMS_CRYPTO Package

The DBMS_CRYPTO package provides several ways to address the security issues that were discussed. (For backward compatibility, DBMS_OBFUSCATION_TOOLKIT is also provided.)

While encryption is not the ideal solution for addressing a number of security threats, it is clear that selectively encrypting sensitive data before storage in the database does improve security. Examples of such data could include:

Oracle Database provides the PL/SQL package DBMS_CRYPTO to encrypt and decrypt stored data. This package supports several industry-standard encryption and hashing algorithms, including the Advanced Encryption Standard (AES) encryption algorithm. AES was approved by the National Institute of Standards and Technology (NIST) to replace the Data Encryption Standard (DES).

The DBMS_CRYPTO package enables encryption and decryption for common Oracle Database data types, 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:

Block cipher modifiers are also provided with DBMS_CRYPTO. You can choose from several padding options, including Public Key Cryptographic Standard (PKCS) #5, and from four block cipher chaining modes, including Cipher Block Chaining (CBC). Padding must be done in multiples of eight bytes.


  • DES is no longer recommended by the National Institute of Standards and Technology (NIST).

  • Usage of SHA-1 is more secure than MD5.

  • Keyed MD5 is not vulnerable.

Table 9-1 compares the DBMS_CRYPTO package features to the other PL/SQL encryption package, the DBMS_OBFUSCATION_TOOLKIT.



Cryptographic algorithms



Padding forms

PKCS5, zeroes

None supported

Block cipher chaining modes



Cryptographic hash algorithms

SHA-1, SHA-1, MD4


Keyed hash (MAC) algorithms


None supported

Cryptographic pseudo-random number generator



Database types



DBMS_CRYPTO is intended to replace the OBFUSCATION_TOOLKIT package, because it is easier to use and supports a range of algorithms that accommodate both new and existing systems. Although 3DES_2KEY and MD4 are provided for backward compatibility, you achieve better security using 3DES, AES, or SHA-1. Therefore, 3DES_2KEY is not recommended.

The DBMS_CRYPTO package includes cryptographic checksum capabilities (MD5), which are useful for comparisons, and the ability to generate a secure random number (the RANDOMBYTES function). Secure random number generation is an important part of cryptography; predictable keys are easily guessed keys; and easily guessed keys may lead to easy decryption of data. Most cryptanalysis is done by finding weak keys or poorly stored keys, rather than through brute force analysis (cycling through all possible keys).


Do not use DBMS_RANDOM, because it is unsuitable for cryptographic key generation.

Key management is programmatic. That is, the application (or caller of the function) must supply the encryption key. This means that the application developer must find a way of storing and retrieving keys securely. The relative strengths and weaknesses of various key management techniques are discussed in the sections that follow. The DBMS_OBFUSCATION_TOOLKIT package, which can handle both string and raw data, requires the submission of a 64-bit key. The DES algorithm itself has an effective key length of 56-bits.


The DBMS_OBFUSCATION_TOOLKIT is granted to PUBLIC by default. Oracle recommends that you revoke this grant.

While the DBMS_OBFUSCATION_TOOLKIT package can take either VARCHAR2 or RAW data types, it is preferable to use the RAW data type for keys and encrypted data. Storing encrypted data as VARCHAR2 can cause problems if it passes through Globalization Support routines. For example, when transferring a database to another database that uses another character set.

To convert between VARCHAR2 and RAW data types, use the CAST_TO_RAW and CAST_TO_VARCHAR2 functions of the UTL_RAW package.

See Also:

9.5 Verifying Data Integrity with the DBMS_SQLHASH Package

This section describes the following topics:

9.5.1 About the DBMS_SQLHASH Package

The DBMS_SQLHASH package can check data integrity by using hash algorithms. It provides an interface to generate the hash value of the result set returned by a SQL query. Hash values are similar to data fingerprints and are used to ensure data integrity. DBMS_SQLHASH provides support for several industry-standard hashing algorithms, including MD4, MD5, and SHA-1 cryptographic hashes.

Oracle Database installs the DBMS_SQLHASH package in the SYS schema. You can then grant package access to existing users and roles as required.

DBMS_SQLHASH includes the GETHASH function that is used to retrieve the hash value of a query result set. The GETHASH function runs one of the supported cryptographic hash algorithms against the result set of the SQL statement to arrive at a hash value.

You can compare hash values to check whether data was altered. For example, before storing data, Jane runs the DBMS_SQLHASH.GETHASH function against the SQL statement to create a hash value of the SQL result set. When she retrieves the stored data at a later date, she reruns the hash function against the SQL statement using the same algorithm. If the second hash value is identical to the first one, then data was not altered. Any modification to the result set data causes the hash value to be different.

9.5.2 Using the DBMS_SQLHASH.GETHASH Function

The DBMS_SQLHASH.GETHASH function applies one of the supported cryptographic hash algorithms to the result set of the SQL statement. Syntax

    sqltext IN varchar2,
    digest_type IN BINARY_INTEGER,
    chunk_size IN number DEFAULT 134217728)
   RETURN raw; Parameters

Table 9-2 lists the GETHASH parameters and their descriptions.

Table 9-2 GETHASH Function Parameters

Parameter Name Description


The SQL statement whose result is hashed.


Hash algorithm used: HASH_MD4, HASH_MD5, or HASH_SH1


Size of the result chunk when getting the hash

When the result set size is large, the GETHASH function breaks it into chunks having a size equal to chunk_size. It generates the hash for each chunk and then uses hash chaining to calculate the final hash. The default chunk_size is 128 megabytes.

9.6 Examples of Using the Data Encryption API

This section provides the following examples:

9.6.1 Example of a Data Encryption Procedure

The following sample PL/SQL program (dbms_crypto.sql) shows how to encrypt data. This example code performs the following actions:

  • Encrypts a string (VARCHAR2 type) using DES after first converting it into the RAW data type.

    This step is necessary because encrypt and decrypt functions and procedures in DBMS_CRYPTO package work on the RAW data type only, unlike functions and packages in the DBMS_OBFUSCATION_TOOLKIT package.

  • Shows how to create a 160-bit hash using SHA-1 algorithm.

  • Demonstrates how MAC, a key-dependent one-way hash, can be computed using the MD5 algorithm.

The dbms_crypto.sql procedure follows:

    input_string     VARCHAR2(16) := 'tigertigertigert';
    raw_input        RAW(128) :=
    key_string       VARCHAR2(8)  := 'scottsco';
    raw_key          RAW(128) :=
    encrypted_raw    RAW(2048);
    encrypted_string VARCHAR2(2048);
    decrypted_raw    RAW(2048);
    decrypted_string VARCHAR2(2048); 
-- 1. Begin testing Encryption 
    dbms_output.put_line('> Input String                     : ' || 
    dbms_output.put_line('> ========= BEGIN TEST Encrypt =========');
    encrypted_raw := dbms_crypto.Encrypt(
        src => raw_input, 
        typ => DBMS_CRYPTO.DES_CBC_PKCS5, 
        key => raw_key);
        dbms_output.put_line('> Encrypted hex value              : ' || 
decrypted_raw := dbms_crypto.Decrypt(
        src => encrypted_raw, 
        typ => DBMS_CRYPTO.DES_CBC_PKCS5, 
        key => raw_key);
    decrypted_string := 
dbms_output.put_line('> Decrypted string output          : ' || 
if input_string = decrypted_string THEN
    dbms_output.put_line('> String DES Encyption and Decryption successful');
END if;
dbms_output.put_line('> ========= BEGIN TEST Hash =========');
    encrypted_raw := dbms_crypto.Hash(
        src => raw_input, 
        typ => DBMS_CRYPTO.HASH_SH1);
dbms_output.put_line('> Hash value of input string       : ' || 
dbms_output.put_line('> ========= BEGIN TEST Mac =========');
    encrypted_raw := dbms_crypto.Mac(
        src => raw_input, 
        typ => DBMS_CRYPTO.HMAC_MD5, 
        key => raw_key);
dbms_output.put_line('> Message Authentication Code      : ' || 
dbms_output.put_line('> End of DBMS_CRYPTO tests  ');

9.6.2 Example of AES 256-Bit Data Encryption and Decryption Procedures

The following PL/SQL block shows how to encrypt and decrypt a predefined variable named input_string using the AES 256-bit algorithm with Cipher Block Chaining and PKCS #5 padding.

   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.CHAIN_CBC
                          + DBMS_CRYPTO.PAD_PKCS5;
   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 in the encrypted_raw variable 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);

9.6.3 Example of Encryption and Decryption Procedures for BLOB Data

The following sample PL/SQL program (blob_test.sql) shows how to encrypt and decrypt BLOB data. This example code does the following, and prints out its progress (or problems) at each step:

  • Creates a table for the BLOB column

  • Inserts the raw values into that table

  • Encrypts the raw data

  • Decrypts the encrypted data

The blob_test.sql procedure follows:

-- Create a table for BLOB column.
create table table_lob (id number, loc blob);

-- insert 3 empty lobs for src/enc/dec
insert into table_lob values (1, EMPTY_BLOB());
insert into table_lob values (2, EMPTY_BLOB());
insert into table_lob values (3, EMPTY_BLOB());

set echo on
set serveroutput on

    srcdata    RAW(1000);
    srcblob    BLOB;
    encrypblob BLOB;
    encrypraw  RAW(1000);
    encrawlen  BINARY_INTEGER;
    decrypblob BLOB;
    decrypraw  RAW(1000);
    decrawlen  BINARY_INTEGER;
    leng       INTEGER;

    -- RAW input data 16 bytes
    srcdata := hextoraw('6D6D6D6D6D6D6D6D6D6D6D6D6D6D6D6D');
    dbms_output.put_line('input is ' || srcdata);
    -- select empty lob locators for src/enc/dec
    select loc into srcblob from table_lob where id = 1;
    select loc into encrypblob from table_lob where id = 2;
    select loc into decrypblob from table_lob where id = 3;
    dbms_output.put_line('Created Empty LOBS');
    leng := DBMS_LOB.GETLENGTH(srcblob);
    IF leng IS NULL THEN
        dbms_output.put_line('Source BLOB Len NULL ');
        dbms_output.put_line('Source BLOB Len ' || leng);
    END IF;
    leng := DBMS_LOB.GETLENGTH(encrypblob);
    IF leng IS NULL THEN
        dbms_output.put_line('Encrypt BLOB Len NULL ');
        dbms_output.put_line('Encrypt BLOB Len ' || leng);
    END IF;
    leng := DBMS_LOB.GETLENGTH(decrypblob);
    IF leng IS NULL THEN
        dbms_output.put_line('Decrypt  BLOB Len NULL ');
        dbms_output.put_line('Decrypt BLOB Len ' || leng);
    END IF;
    -- write source raw data into blob
    DBMS_LOB.OPEN (srcblob, DBMS_LOB.lob_readwrite);
    DBMS_LOB.WRITEAPPEND (srcblob, 16, srcdata);
    DBMS_LOB.CLOSE (srcblob);
    dbms_output.put_line('Source raw data written to source blob');
    leng := DBMS_LOB.GETLENGTH(srcblob);
    IF leng IS NULL THEN
        dbms_output.put_line('source BLOB Len NULL ');
        dbms_output.put_line('Source BLOB Len ' || leng);
    END IF;
    * Procedure Encrypt
    * Arguments: srcblob -> Source BLOB
    *            encrypblob -> Output BLOB for encrypted data
    *            DBMS_CRYPTO.AES_CBC_PKCS5 -> Algo : AES
    *                                         Chaining : CBC
    *                                         Padding : PKCS5
    *            256 bit key for AES passed as RAW
    *                ->
    *            IV (Initialization Vector) for AES algo passed as RAW
    *                -> hextoraw('00000000000000000000000000000000')
                hextoraw ('000102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F'),
    dbms_output.put_line('Encryption Done');
    leng := DBMS_LOB.GETLENGTH(encrypblob);
    IF leng IS NULL THEN
        dbms_output.put_line('Encrypt BLOB Len NULL');
        dbms_output.put_line('Encrypt BLOB Len ' || leng);
    END IF;
    -- Read encrypblob to a raw
    encrawlen := 999;
    DBMS_LOB.OPEN (encrypblob, DBMS_LOB.lob_readwrite);
    DBMS_LOB.READ (encrypblob, encrawlen, 1, encrypraw);
    DBMS_LOB.CLOSE (encrypblob);
    dbms_output.put_line('Read encrypt blob to a raw');
    dbms_output.put_line('Encrypted data is (256 bit key) ' || encrypraw);
    * Procedure Decrypt
    * Arguments: encrypblob -> Encrypted BLOB to decrypt
    *            decrypblob -> Output BLOB for decrypted data in RAW
    *            DBMS_CRYPTO.AES_CBC_PKCS5 -> Algo : AES
    *                                         Chaining : CBC
    *                                         Padding : PKCS5
    *            256 bit key for AES passed as RAW (same as used during Encrypt)
    *                ->
    *            IV (Initialization Vector) for AES algo passed as RAW (same as
                 used during Encrypt)
    *                -> hextoraw('00000000000000000000000000000000')
    leng := DBMS_LOB.GETLENGTH(decrypblob);
    IF leng IS NULL THEN
        dbms_output.put_line('Decrypt BLOB Len NULL');
        dbms_output.put_line('Decrypt BLOB Len ' || leng);
    END IF;
    -- Read decrypblob to a raw
    decrawlen := 999;
    DBMS_LOB.OPEN (decrypblob, DBMS_LOB.lob_readwrite);
    DBMS_LOB.READ (decrypblob, decrawlen, 1, decrypraw);
    DBMS_LOB.CLOSE (decrypblob);
    dbms_output.put_line('Decrypted data is (256 bit key) ' || decrypraw);
    DBMS_LOB.OPEN (srcblob, DBMS_LOB.lob_readwrite);
    DBMS_LOB.TRIM (srcblob, 0);
    DBMS_LOB.CLOSE (srcblob);
    DBMS_LOB.OPEN (encrypblob, DBMS_LOB.lob_readwrite);
    DBMS_LOB.TRIM (encrypblob, 0);
    DBMS_LOB.CLOSE (encrypblob);
    DBMS_LOB.OPEN (decrypblob, DBMS_LOB.lob_readwrite);
    DBMS_LOB.TRIM (decrypblob, 0);
    DBMS_LOB.CLOSE (decrypblob);

truncate table table_lob;
drop table table_lob;

9.7 Finding Information About Encrypted Data

Table 9-3 lists data dictionary views that you can query to access information about encrypted data. See Oracle Database Reference for detailed information about these views.

Table 9-3 Views That Display Information about Encrypted Data

View Description


Describes encryption algorithm information for all encrypted columns in all tables accessible to the user


Describes encryption algorithm information for all encrypted columns in the database


Describes encryption algorithm information for all encrypted columns in all tables in the schema of the user


Displays information about the tablespaces that are encrypted


Displays information on the status of the wallet and the wallet location for transparent data encryption


Displays supported encryption algorithms.