24 DBMS_CRYPTO

Using the DBMS_CRYPTO Subprograms

• Overview

• Security Model

• Types

• Algorithms

• Restrictions

• Exceptions

• Operational Notes

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Overview

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).

Table 24-1 lists the DBMS_CRYPTO package features in comparison to the other PL/SQL encryption package, the DBMS_OBFUSCATION_TOOLKIT.

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.

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Security Model

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

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Types

Parameters for the DBMS_CRYPTO subprograms use these datatypes:

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Algorithms

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

^Footnote 1 Complies with IETF RFC 2104 standard

^Footnote 1 See Table 24-5, "DBMS_CRYPTO Encryption Algorithms"

^Footnote 2 See Table 24-7, "DBMS_CRYPTO Block Cipher Chaining Modifiers"

^Footnote 3 See Table 24-8, "DBMS_CRYPTO Block Cipher Padding Modifiers"

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Restrictions

The VARCHAR2 datatype is not directly supported by DBMS_CRYPTO. Before you can perform cryptographic operations on data of the type VARCHAR2, you must convert it to the uniform database character set AL32UTF8, and then convert it to the RAW datatype. After performing these conversions, you can then encrypt it with the DBMS_CRYPTO package.

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Exceptions

Table 24-9 lists exceptions that have been defined for DBMS_CRYPTO.

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Operational Notes

• When to Use Encrypt and Decrypt Procedures or Functions

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

• About Generating and Storing Encryption Keys

• Conversion Rules

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 semiweak keys. Keys are considered weak or semiweak 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 semiweak 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');
  

  See Also:

  Chapter 170, "UTL_I18N" for information about using the UTL_I18N PL/SQL package.

• If you want to store encrypted data of the RAW datatype in a VARCHAR2 database column, then use RAWTOHEX or UTL_ENCODE.BASE64_ENCODE to make it suitable for VARCHAR2 storage. These functions expand data size by 2 and 4/3, respectively.

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Examples

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;

Summary of DBMS_CRYPTO Subprograms

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DECRYPT Function

This function decrypts RAW data using a stream or block cipher with a user supplied key and optional IV (initialization vector).

Syntax

DBMS_CRYPTO.DECRYPT(
   src IN RAW,
   typ IN PLS_INTEGER,
   key IN RAW,
   iv  IN RAW          DEFAULT NULL)
 RETURN RAW;

Pragmas

pragma restrict_references(decrypt,WNDS,RNDS,WNPS,RNPS);

Parameters

Usage Notes

• To retrieve original plaintext data, DECRYPT must be called with the same cipher, modifiers, key, and IV that was used to encrypt the data originally.

  See Also:

  "Usage Notes" for the ENCRYPT function for additional information about the ciphers and modifiers available with this package.

• If VARCHAR2 data is converted to RAW before encryption, then it must be converted back to the appropriate database character set by using the UTL_I18N package.

  See Also:

  "Conversion Rules" for a discussion of the VARCHAR2 to RAW conversion process.

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DECRYPT Procedures

These procedures decrypt LOB data using a stream or block cipher with a user supplied key and optional IV (initialization vector).

Syntax

DBMS_CRYPTO.DECRYPT(
   dst IN OUT NOCOPY BLOB,
   src IN            BLOB,
   typ IN            PLS_INTEGER,
   key IN            RAW,
   iv  IN            RAW          DEFAULT NULL);

DBMS_CRYPT.DECRYPT(
   dst IN OUT NOCOPY CLOB         CHARACTER SET ANY_CS,
   src IN            BLOB,
   typ IN            PLS_INTEGER,
   key IN            RAW,
   iv  IN            RAW          DEFAULT NULL);

Pragmas

pragma restrict_references(decrypt,WNDS,RNDS,WNPS,RNPS);

Parameters

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ENCRYPT Function

This function encrypts RAW data using a stream or block cipher with a user supplied key and optional IV (initialization vector).

Syntax

DBMS_CRYPTO.ENCRYPT(
   src IN RAW,
   typ IN PLS_INTEGER,
   key IN RAW,
   iv  IN RAW          DEFAULT NULL)
 RETURN RAW;

Pragmas

pragma restrict_references(encrypt,WNDS,RNDS,WNPS,RNPS);

Parameters

Usage Notes

• Block ciphers may be modified with chaining and padding type modifiers. The chaining and padding type modifiers are added to the block cipher to produce a cipher suite. Cipher Block Chaining (CBC) is the most commonly used chaining type, and PKCS #5 is the recommended padding type. See Table 24-7 and Table 24-8 for block cipher chaining and padding modifier constants that have been defined for this package.

• To improve readability, you can define your own package-level constants to represent the cipher suites you use for encryption and decryption. For example, the following example defines a cipher suite that uses DES, cipher block chaining mode, and no padding:

  DES_CBC_NONE CONSTANT PLS_INTEGER := DBMS_CRYPTO.ENCRYPT_DES
                                       + DBMS_CRYPTO.CHAIN_CBC
                                       + DBMS_CRYPTO.PAD_NONE;
  

  See Table 24-6 for the block cipher suites already defined as constants for this package.

• To encrypt VARCHAR2 data, it should first be converted to the AL32UTF8 character set.

  See Also:

  "Conversion Rules" for a discussion of the conversion process.

• Stream ciphers, such as RC4, are not recommended for stored data encryption.

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ENCRYPT Procedures

These procedures encrypt LOB data using a stream or block cipher with a user supplied key and optional IV (initialization vector).

Syntax

DBMS_CRYPTO.ENCRYPT(
   dst IN OUT NOCOPY BLOB,
   src IN            BLOB,
   typ IN            PLS_INTEGER,
   key IN            RAW,
   iv  IN            RAW          DEFAULT NULL);

DBMS_CRYPTO.ENCRYPT(
   dst IN OUT NOCOPY BLOB,
   src IN            CLOB         CHARACTER SET ANY_CS,
   typ IN            PLS_INTEGER,
   key IN            RAW,
   iv  IN            RAW          DEFAULT NULL);

Pragmas

pragma restrict_references(encrypt,WNDS,RNDS,WNPS,RNPS);

Parameters

Usage Notes

See "Conversion Rules" for usage notes about using the ENCRYPT procedure.

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HASH Function

A one-way hash function takes a variable-length input string, the data, and converts it to a fixed-length (generally smaller) output string called a hash value. The hash value serves as a unique identifier (like a fingerprint) of the input data. You can use the hash value to verify whether data has been changed or not.

Note that a one-way hash function is a hash function that works in one direction. It is easy to compute a hash value from the input data, but it is hard to generate data that hashes to a particular value. Consequently, one-way hash functions work well to ensure data integrity. Refer to "When to Use Hash or Message Authentication Code (MAC) Functions" for more information about using one-way hash functions.

This function applies to data one of the supported cryptographic hash algorithms listed in Table 24-3.

Syntax

DBMS_CRYPTO.Hash (
   src IN RAW,
   typ IN PLS_INTEGER)
 RETURN RAW;

DBMS_CRYPTO.Hash (
   src IN BLOB,
   typ IN PLS_INTEGER)
 RETURN RAW;

DBMS_CRYPTO.Hash (
   src IN CLOB CHARACTER SET ANY_CS,
   typ IN PLS_INTEGER)
 RETURN RAW;

Pragmas

pragma restrict_references(hash,WNDS,RNDS,WNPS,RNPS);

Parameters

Usage Note

Oracle recommends that you use the SHA-1 (Secure Hash Algorithm), specified with the constant, HASH_SH1, because it is more resistant to brute-force attacks than MD4 or MD5. If you must use a Message Digest algorithm, then MD5 provides greater security than MD4.

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MAC Function

A Message Authentication Code, or MAC, is a key-dependent one-way hash function. MACs have the same properties as the one-way hash function described in "HASH Function", but they also include a key. Only someone with the identical key can verify the hash. Also refer to "When to Use Hash or Message Authentication Code (MAC) Functions" for more information about using MACs.

This function applies MAC algorithms to data to provide keyed message protection. See Table 24-4 for a list of MAC algorithms that have been defined for this package.

Syntax

DBMS_CRYPTO.MAC (
   src IN RAW,
   typ IN PLS_INTEGER,
   key IN RAW)
 RETURN RAW;

DBMS_CRYPTO.MAC (
   src IN BLOB,
   typ IN PLS_INTEGER
   key IN RAW)
 RETURN RAW;

DBMS_CRYPTO.MAC (
   src IN CLOB CHARACTER SET ANY_CS,
   typ IN PLS_INTEGER
   key IN RAW)
 RETURN RAW;

Pragmas

pragma restrict_references(mac,WNDS,RNDS,WNPS,RNPS);

Parameters

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RANDOMBYTES Function

This function returns a RAW value containing a cryptographically secure pseudo-random sequence of bytes, which can be used to generate random material for encryption keys. The RANDOMBYTES function is based on the RSA X9.31 PRNG (Pseudo-Random Number Generator), and it draws its entropy (seed) from the sqlnet.ora file parameter SQLNET.CRYPTO_SEED.

Syntax

DBMS_CRYPTO.RANDOMBYTES (
   number_bytes IN POSITIVE)
 RETURN RAW;

Pragmas

pragma restrict_references(randombytes,WNDS,RNDS,WNPS,RNPS);

Parameters

Usage Note

• The number_bytes value should not exceed the maximum length of a RAW variable.

• The SQLNET.CRYPTO_SEED parameter can be set by entering 10 to 70 random characters with the following syntax in the sqlnet.ora file:

  SQLNET.CRYPTO_SEED = <10 to 70 random characters>
  

  See Also:

  Oracle Database Advanced Security Administrator's Guide for more information about the SQLNET.CRYPTO_SEED parameter and its use.

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RANDOMINTEGER Function

This function returns an integer in the complete range available for the Oracle BINARY_INTEGER datatype.

Syntax

DBMS_CRYPTO.RANDOMINTEGER
 RETURN BINARY_INTEGER;

Pragmas

pragma restrict_references(randominteger,WNDS,RNDS,WNPS,RNPS);

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RANDOMNUMBER Function

This function returns an integer in the Oracle NUMBER datatype in the range of [0..2**128-1].

Syntax

DBMS_CRYPTO.RANDOMNUMBER
 RETURN NUMBER;

Pragmas

pragma restrict_references(randomnumber,WNDS,RNDS,WNPS,RNPS);