This research paper explores the use of cryptography in database security. It specifically covers applications of encryption in authentication, transmission of data between client and server, and protection of stored content. This paper begins with an overview of encryption techniques, specifically symmetric and asymmetric encryption. It follows with a specific discussion about the use of cryptography in database solutions. The paper concludes with a short summary of commercial solutions intended for increasing the security of database content and client/server transactions.Whitfield Diffie, a cryptographic researcher and Sun Microsystems CSO says, “Cryptography is the most flexible way we know of protecting [data and] communications in channels that we don’t control.” (Carpenter, 2007). Cryptography is “the enciphering [encryption] and deciphering [decryption] of messages in secret code or cipher; the computerized encoding and decoding of information.” (CRYPTO, 2009). There are two primary means of encryption in use today. They are symmetric key encryption and asymmetric key encryption. Symmetric key encryption uses a single key to encrypt and decrypt information. Asymmetric key encryption, also known as public key cryptography uses two keys - one to encrypt information and a second key to decrypt information. In addition to encryption and decryption, public-key cryptography can be used to create and verify digital signatures of blocks of text or binary data without encrypting them. A digital signature is a small block of information cryptographically generated from content, like an email message or an installation program for software. The private key in the asymmetric solution can be used to create a digital signature of data, while the public key verifies the integrity of data and related digital signature that was created using the private key. The main advantage of public key cryptography over the symmetric key system is that the public key can be given away, as the name implies - made public. Anyone with a public key can encrypt a message and only the holder of the matching private key can decrypt that message. In the symmetric system, all parties must hold the same key.Public key cryptography can be used to verify the identity of an individual, application or computer system. As a simple example, let us say I have an asymmetric key pair and provide you with my public key. You can be a human or a software application. As long as I keep my private key protected so that no one else can obtain it, only I can generate a digital signature that you can use with my public key to prove mathematically that the signature only came from me. This approach is much more robust and less susceptible to attack than the traditional username and password approach.Application of cryptography does not come without the overhead of ongoing management of the technology. In a past interview (Carpenter, 2007), Whitfield Diffie, a co-inventor of public key cryptography says the main detractor from widespread adoption of strong encryption within I.T. infrastructures is key management - the small strings of data that keep encrypted data from being deciphered. Proper integration of cryptographic technologies into a database infrastructure can provide protection beyond username and password authentication and authorization. It can absolutely prevent anyone from reading sensitive data during transmission or stored on media.Some U.S. government standards require the use of encryption for stored and transmitted personal information. Grimes (2006) details the recent laws passed in the United States requiring the protection of personal data. These laws include the Gramm-Leach-Bliley Act for protection of consumer financial data, the Health Insurance Portability and Accountability Act for personal health-related data, and the Electronic Communications Privacy Act, which gives broad legal protection to electronically transmitted data.As discussed above, public key cryptography can be used to authenticate a person, application or computer using digital signature technology. A database management system enhanced to use public keys for authentication would store those keys and associate them with specific users. The client would use their private key to sign a small block of data that was randomly chosen by the server. The client would return a digital signature of that data, which the server could verify using the stored public keys of the various users. A verification match would identify the specific user.The second application of encryption technology in database security is used to protect transmission of data between a client and server. The client may be a web-based application running on a separate server and communicating over a local network, or it may be a fat-client located in another department or at some other location on the Internet. A technology called TLS can be used to provide confidentiality of all communications between the client and server, i.e. the database connection. “Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic protocols that provide security and data integrity for communications over networks such as the Internet.” (TLS, 2009). Web servers and browsers use the TLS protocol to protect data transmissions such as credit card numbers or other personal information. The technology can be used to protect any data transmission for any type of client-server solution, include database systems. TLS also has authentication capability using public key cryptography. This type of authentication would only allow known public keys to make a connection. This approach is not integrated at a higher level in the solution, such as the application level.Finally, cryptography can be used to protect the entire content of database storage, specific tables or columns of table data. Encrypting stored content can protect sensitive data from access within the database management system, through loss of the storage media, and an external process that reads raw data blocks from the media. The extent to which stored content is encrypted must be weighed against the overhead of encrypting and decrypting data for transaction-intense systems. Britt (2006) stresses the importance of selectively encrypting only those portions of the content that are evaluated to be a security risk if released into the public. He says a “[…] misconception is that adding encryption will put a tremendous strain on database performance during queries and loads.” This type of protection often uses symmetric key encryption because it is much faster than the public key solution.Marwitz (2008) describes several levels of database content encryption available in Microsoft SQL Server 2005 and 2008. SQL Server 2008 provides the ability to use public key authentication directly in the access control subsystem. Additionally, the entire database server storage, individual databases and table columns can be encrypted using public key encryption. (SQLS, 2009). Table columns, such as those used to store social security numbers, credit card number, or any other sensitive personal information are a good choice for performance sensitive systems. Use of this capability means that the only way to obtain access to the unencrypted data within a column of a database table protected in this manner is to use the private key of an individual who has been granted access. The user’s private key is used to authenticate and gain access to information in the database. Extra protection is gained since the private key is never co-located with the encrypted data.IBM’s DB2 product supports a number of different cryptographic capabilities and attempts to leverage as many of those capabilities that are present in the hosting operating system - Intel-based, minicomputer or mainframe. Authentication to the database from a client can be performed over a variety of encrypted connection types or using Kerberos key exchange. DB2 also supports the concept of authentication plug-ins that can be used with encrypted connections. After authentication has succeeded, DB2 can provide client-server data transmission over a TLS connection and optionally validate the connection using public key cryptography. Like Microsoft SQL Server, the most recent releases of DB2 can encrypt the entire storage area, single databases, or specific columns within the database. (DB2, 2009).This paper provided a broad survey of how cryptographic technologies can raise the security posture of database solutions. Cryptography is becoming a common tool to solve many problems of privacy and protection of sensitive information in growing warehouses of online personal information. This paper described the use of cryptography in database client authentication, transmission of transaction data, and protection of stored content. Two commercial products’ cryptographic capabilities were explored in the concluding discussion. There are more commercial, free and open source solutions for protecting database systems not mentioned in this paper. As citizens and government continue to place pressure on institutions to protect private information, expect to see the landscape of cryptographic technologies for database management systems expand.ReferencesBritt, P. (2006). The encryption code. Information Today. March 2006, vol. 23, issue 3.Carpenter, J. (2007). The grill: an interview with Whitfield Diffie. Computerworld. August 27, 2007. Page 24.CRYPTO. (2009). Definition of cryptography. Retrieved 18 July 2009 from http://www.merriam-webster.com/dictionary/cryptography.DB2. (2009). DB2 Security Model Overview. Retrieved 18 July 2009 from http://publib.boulder.ibm.com/infocenter/db2luw/v9r7/topic/com.ibm.db2.luw.admin.sec.doc/doc/c0021804.html.Grimes, R. A. (2006). End-to-end encryption strategies. Infoworld. September 4, 2006. Page 31.Marwitz, C. (2008). Database encryption solutions: protect your databases - and your company - from attacks and leaks. SQL Server Magazine. September 2008.SQLS. (2009). Cryptography in SQL Server. Retrieved 18 July 2009 from http://technet.microsoft.com/en-us/library/cc837966.aspx.TLS. (2009). Transport layer security. Retrieved 18 July 2009 from http://en.wikipedia.org/wiki/Transport_Layer_Security.