Secure XML: The New Syntax for Signatures and Encryption

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 ...