DATABASE SECURITY - Database Design and Development: An Essential Guide for IT Professionals - page 513

• Choose two large, random prime numbers n1 and n2.
• Compute the product of n1 and n2. This product is also known as the limit L,
assumed to be larger than the largest integer ever needed to be encoded.
• Choose a prime number larger than both n1 and n2 as the public key P
• Choose the private key R in a special way based on n1, n2, and P

[If you are interested, R is calculated such that R * P = 1, modulo (n1-1) * (n2-1).]
The limit L and the public key P are made known publicly. Note that the private
key R may be computed easily if the public key P and the prime numbers n1 and
n2 are given. However, it is extremely difficult to compute the private key R if just
the public key P and the limit L are known. This is because finding the prime factors
of L is almost impossible if L is fairly large.

Data Exchange Example Let us consider the use of public key encryption in a
banking application. Here are the assumptions:

• Online requests for fund transfers may be made to a bank called ABCD. The
bank's customer known as Good places a request to transfer $1 million.
• The bank must be able to understand and acknowledge the request.
• The bank must be able to verify that the fund transfer request was in fact made
by customer Good and not anyone else.
• Also, customer Good must not be able to allege that the request was made up
by the bank to siphon funds from Good's account.

Figure 16-12 illustrates the use of public key encryption technique showing the
banking transaction. Note how each transfer is coded and decoded.

ABCD Bank

Public Algorithm:
Encryption EE,
Decryption DD

Private Key:
ABCD-d

Meaningless
Text

Fund Transfer
Request

Apply
Good-e, EE

Meaningless
Text

Apply
ABCD-d,
DD

Meaningless
Text

Fund Transfer
Request

Private Key:
Good-d

Apply
ABCD-e,
EE

Public Keys
ABCD-e
Good-e

Apply
Good-d, DD

Customer Mr. Good

Figure 16-12 Public key encryption: data exchange.