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Secure XML: The New Syntax for Signatures and Encryption by Kitty Niles, Donald E. Eastlake

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2.3. Secret or Symmetric Key Ciphers

Secret key ciphers have been known for centuries, although the oldest were weak and had no key. Today's modern ciphers involve a reversible data scrambling system such that it is computationally infeasible to recover the unscrambled data without knowledge of the secret key used to scramble that data. See Figure 2-3. The original version is called the plain text; the scrambled version is called the cipher text.

Figure 2-3. Secret key encryption

Perhaps the best-known symmetric cipher is the Data Encryption Standard (DES [FIPS 186-2]). With 56 bits of actual key and a number of weaknesses, DES is not considered ...

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