So far, this chapter has been concerned with permissions. The last topic to be covered is totally unrelated to permissions. A message digest, which is not unique to Java, is a hash value for a message. More specifically, a message digest is the following:
A unique binary hash value for a specific message. No two messages will produce the same message digest value.
A value computed using a message digest algorithm (not covered here)
A hash value that cannot be used to determine the original message. Actually, it is possible to get the original message from the message digest, but statistically speaking, the sun will burn out before then, so for all practical purposes, it is impossible.
Because a specific message digest will be computed ...