Re: [GNU Crypto] Perhaps OT crypto question

[Casey Marshall]

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>>>>> "Ben" == Ben  <address@hidden> writes:

Ben> Maybe this is the wrong place for this question, but here goes:
Ben> Say I have some data d.  I have a symmetric block cipher like
Ben> Blowfish that encrypts the data such that e = b(d, k) with k
Ben> being the key, d the original data, and e the encrypted data.
Ben> Now I have a hash function like SHA that takes the hash of the
Ben> encrypted data like this h = s(e) or h = s(b(d, k)).  Now,
Ben> assuming that an attacker can see only the data (d) and the hash
Ben> of the encrypted data (h or s(b(d, k))).  Would my key (k) be
Ben> secure?

Looks like. Is this a MAC? If so there are constructions as secure as
this but more useful.

- -- 
Casey Marshall || address@hidden
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