Computers
A computer is a general-purpose machine that can run a variety of programs, including programs to produce ciphers and codes of unfathomable complexity. The same concepts described earlier in the article apply to cryptography with computers, but computers are so fast that the algorithms can be much more complicated. The rise in computer use in the 1960s initiated the age of computational cryptography. Computers, when properly programmed, give users an excellent tool to encrypt messages and maintain the privacy of their communications, and computer programmers have developed many encryption algorithms.
Recall that Computers function with a language of binary num- bers – 1s and 0s. A bit is one unit of information, either a 1 or 0, and computer data and instructions consist of strings of bits representing numbers or commands.
When corporations and governments began computerizing their daily operations in the 1960s, there were many types of computers and software, and few standards or common procedures existed among the different varieties. Sending encrypted messages within a company or branch of government was not a problem because everyone was using the same computers and algorithms, but sending encrypted messages to another organization presented a difficulty. Since each business or government office had its own encryption techniques and algorithms, communication between them was not possible. The recipient must have the key and how it is used – the algorithm – in order to decipher the message.
Computers are fast, so encryption algorithms can be complex, but computers can also be programmed to decrypt by trying guesses, speeding up the cryptanalyst’s work. People began to wonder if 56 bits was enough. This number of keys was lower than the possible ciphers of the old monoalphabetic cipher, which had been broken long ago. But an important factor was the lack of structure or patterns in a correctly performed encryption algorithm, which did not allow frequency analysis or other guessing schemes to work. Breaking a perfect encryption algorithm would require brute force, checking each possibility one at a time. Even computers, at least in the 1970s, were not fast enough to succeed in a reasonable amount of time.
There were other issues as well. Making a powerful encryption scheme available to anyone also makes it available to thieves, terrorists, and spies. As described in the following sidebar, the United States cryptology agency, the National Security Agency (NSA), is responsible for protecting government information as well as collecting intelligence from the transmissions and communications of potentially hostile organizations. The agency’s mission involves a considerable amount of cryptography and cryptanalysis. Government officials and the IBM scientists who developed DES deemed a 56-bit key to be sufficient protection for normal circumstances, since in 1976 most computers could not reasonably be expected to succeed in a brute-force analysis. But the nearly inexhaustible resources of the United States government might have succeeded if necessary, which could have given NSA a chance to decipher messages. This would not have been the case if the standard had employed a larger key.
NSA may or may not have been able to read DES with 56-bit key when it was first adopted – few people outside of the agency can be sure, since NSA is not in the habit of divulging secrets – but advances in computer technology and speed made a 56-bit key obsolete anyway. A standard known as Advanced Encryption Standard (AES) superseded DES in 2001. The key size in AES can be up to 256 bits, a number exceeding 1077.
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