Download eBook (PDF) - Red Gate Software

7 – One-Way Encryption• Security vulnerabilities of data in transit – the Hashbytes methodrequires the passing of plain text into its arguments. This plain textvalue can be disclosed through using SQL Server Profiler, or any otherdatabase transaction monitoring tool.Known VulnerabilitiesThe Payment Card Industry Data Security Standard (PCI DSS), throughrequirement 3.4, does offer one-way encryption as a valid option in storing theprimary account number, which is considered sensitive, in a database. Thecaveat is that the one-way encryption must use a strong algorithm. Among thealgorithm options that are available to one-way encryption in SQL Server, PCIDSS defines the SHA1 algorithm as being considered "… an example of anindustry-tested and accepted hashing algorithm.", which is anacknowledgement that SHA1 meets this criteria. For details regarding all of thealgorithm options available with the Hashbytes method, see Chapter 4.The following sections review a few of the most common knownvulnerabilities, when using one-way encryption:Dictionary Attack VulnerabilityA dictionary attack is one in which a list of values are hashed and thencompared to the hash values stored in the target data table. This method is oftenused in an attempt to reveal passwords that are protected using one-wayencryption.By way of an example, consider an attempted dictionary attack is on theBorrower_Identification table of our HomeLending database, whichwe've protected using one-way encryption. Within theIdentification_Value column are the hash values of Social SecurityNumbers that are generated through one-way encryption.The attack, depicted in Figure 7-2, is executed as follows:• The attacker has created an "Attack Dictionary" of hash values that arebased upon a sequence of plain text Social Security Numbers, rangingfrom "555-86-0622" through "555-86-0626".• Each of the hash values in the attack dictionary is compared to thehash values stored in the Borrower_Identification table.150