Thursday, July 06, 2006

More on cryptograms

Of course, the Data Encryption Standard and its replacement, the Advanced Encryption Standard, use forms of block coding more complex than the example I gave. However, they do not employ dummy bit strings.
The AES is reportedly secure enough for even U.S. government classified matter. But, there may be a problem in who gets to use it. These programs are licensed by the feds, who obviously require that keys be shared with them. Additionally, there are export controls on advanced encryption systems based on number of bits in the block.
One may of course download a free encryption system such as PGP. The problem is that the web site may be compromised and the received program contain a hidden backdoor for secret monitors.
This is why it may make sense to design one's own encryption system, using ideas such as those I have sketched.
In particular, the first cipher I posted is impervious to any useful statistical analysis provided the key is changed at proper intervals.

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