Substitution Cipher

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What Does Substitution Cipher Mean?

A substitution cipher is a type of encryption where characters or units of text are replaced by others in order to encrypt a text sequence. Substitution ciphers are a part of early cryptography, predating the evolution of computers, and are now relatively obsolete.

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Techopedia Explains Substitution Cipher

In a substitution cipher, a letter such as A or T, is transposed into some other letter, which effectively encrypts the sequence to a human reader. The issue is that simple substitution ciphers do not really encrypt effectively in terms of computer evaluation – with the rise of the personal computer, substitution ciphers became relatively easy for computers to crack. However, some of the ideas behind the substitution cipher continue to live on – some forms of modern encryption might use an extremely large text set and an extremely sophisticated substitution to effectively encrypt information.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.