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Re: [openpgp] 4880bis: Update S2K

2015-04-23 14:36:08
On 04/23/2015 06:52 PM, Earle Lowe wrote:
Assume iteration count to mean "the number of times I call the hash
function - eg the number of times I call Sha256()" (this is my
understanding of the typical work factor eg for PBKDF2)

Ok, I'm on the same boat

The OpenPGP work factor is a count of bytes to hash. 

Ok, now I got the point, thanks :)

If the hash
function hashes 32 bytes, then I would call that hash function "count /
32" - as each invocation gives me 32 bytes.

As far as I know, the input to a hash function has a very large limit on
its maximum size (2^64 for SHA-2-... functions), so, if I get that
correctly, this means that given a count value C , the hash function
gets called:

(C- (size of passwd+salt)) / output_hash_size

correct?
(which, on a curious side note means "the longer the password+salt, the
lesser the amount of calls to the hash function", although the
computation effort is substantially the same)

Cheers

Alessandro

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