Re: How much entropy in a key press?

[Adam Shostack <adam@bwh.harvard.edu>]

Shannon estimates roughly 1 bit per character of English.  

RFC 1750  D. Eastlake, S. Crocker, J. Schiller,
"Randomness Recommendations for Security" is probably useful.

Adam

| 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?
| 
| 

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"It is seldom that liberty of any kind is lost all at once."
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