Password vs data entropy

[Alex Pankratov]

Say, we have a random value of 4 kilobits that someone wants 
to keep secret by the means of protecting it with a password. 

Empirical entropy estimate for an English text is 1.3 bits of 
randomness per character, IIRC.

Assuming the password is an English word or a phrase, and the 
secret is truly random, does it mean that the password needs 
to be 3100+ characters in size in order to provide a "proper"
degree of protection to the value ? 

Or, rephrasing, what should the entropy of the password be 
compared to the entropy of the value being protected (under
whatever keying/encryption scheme) ? 

I realize that this is rather .. err .. open-ended question, 
and it depends on what one means by "protected", but I'm sure 
you can see the gist of the question. How would one deem a
password random enough to be fit for protecting an equivalent
of N bits of random data ? Is it a 1-to-1 ratio ?

Thanks,
Alex

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