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How much entropy in a key press?
Can anyone tell me how many bits of entropy there are per 7-bit ASCII
character. More specifically, a program wishes to generate a session
key by prompting the user to type N random key presses. The characters
entered are hashed down to 128 bits by MD5 for subsequent use as a key.
What should the value of N be, such that the entropy of the user's
string does not unnecessarily exceed the entropy of the hash?