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7 – One-Way Encryptionmillions of records, the attacker would require a large attack dictionary to coverthe possible combinations of plain text and hash values. This would result in along running attack that requires a lot of resources from the database server,therefore increasing the risk of the attack being detected.Therefore, the rainbow table attack was developed. The key player in this gameis the rainbow table. The rainbow table consists of a series of rows holdingtwo columns of data. The first column contains the plain text values that arebeing sought, for example a Social Security Number. The second columncontains a value that is the ending hash of a reduction chain. A reductionchain is the result of taking the plain text value in the first column of ourrainbow table and creating an initial hash; then, a portion of the initial hash,such as its first six digits, is obtained and another hash value is generated. Thisprocess continues for a number of iterations until an ending hash is derived.The ending hash that is stored in the rainbow table represents an array of hashvalues that can be programmatically derived and iterated in an attack, throughthe reversal of the reduction chain building process. This approach provides avery efficient means of storing the seed values that are used to mount an attackon one-way encrypted data.Figure 7-3: The creation of a rainbow table.Let's consider an example of how this type of an attack can affect the sensitivedata that is protected with one-way encryption. As before, we'll assume that arainbow table attack is in progress on the Borrower_Identificationtable of our HomeLending database.The attacker has created a rainbow table, with a reduction chain represented byeach record's last link, based upon a sequence of plain text Social SecurityNumbers ranging from "555-86-0622" through "555-86-0626", as shown inTable 7-1.152