How long does it take to break strong encryption? Encryption
methods can be broken by the use of expensive, specialized, code-breaking
computers. The cost of these machines is substantial, but not beyond the
reach of government agencies, major corporations, and organized crime.
Encryption methods can also be broken by standard computer hardware—
supercomputers, mainframes, workstations, and even personal computers.
These computers break codes using a brute force attack, which consists of
trying all possible keys (Figure 5-56).
The length of a computer-readable encryption key is measured in bits.
A 32-bit key, for example, could be one of 4.2 billion (232) numbers.
Surprisingly, it would be possible to try all these numbers and discover the
key in less than a day by using an average personal computer.
To discover a 40-bit key, you would have to try about 1 trillion possible
combinations—a week’s worth of processing time on a personal computer.
768-bit encryption—once thought to be unbreakable by any computer in
the private sector—requires a lot of computing power, but has been broken
by combining the power of many personal computers connected over the
Internet. Most encryption today uses a 128-bit key, which is secure from
casual hackers.
Another way to understand how the length of a key affects the strength of
encryption is to consider this guideline: Beginning with a 40-bit key, each
additional bit doubles the time it would take to discover the key. If a per-
sonal computer takes one week to crack a 40-bit key, it takes two weeks
to crack a 41-bit key, four weeks to crack a 42-bit key, and eight weeks to
crack a 43-bit key. A 128-bit key takes 2(128-40)
times longer to crack than a
40-bit key—that’s 309,485,009,821,345,068,724,781,056 times longer!
What’s public key encryption? Caesar’s encryption method is an
example of symmetric key encryption in which the key used to encrypt
a message is also used to decrypt the message. Symmetric key encryp-
tion is used to encrypt stationary data, such as corporate financial records.
It is also used to encrypt the data that travels over wireless LANs.
Symmetric keys are not practical for e-mail and other situations in which
the person receiving encrypted data does not have the key beforehand.
E-mailing the key would be a major security problem because of the poten-
tial for a hacker to intercept it.
Public key encryption (PKE) eliminates the key-distribution problem by
using one key to encrypt a message, but another key to decrypt the mes-
sage. Figure 5-57 illustrates how public key encryption works.
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