howto do a hash

Sergi Blanch i Torné sergi at
Fri Jan 2 11:36:44 CET 2009


Understood, and also I feel little silly, the way is so similar to what was 
write for the gnupg-1.4 patch. The encrypt ecc algorithm is very similar to 
what we did, but with a couple of details different.

What I write now is similar. I avoid here error checks and memory wipes.

gcry_md_hd_t hd;
int algo;

if (kek_len == 128) algo=GCRY_MD_SHA256;
else if (kek_len == 192) algo=GCRY_MD_SHA384;
else if (kek_len == 256) algo=GCRY_MD_SHA512;

err = gcry_md_open(&hd,algo,GCRY_MD_FLAG_SECURE);
err = gcry_md_enable(hd,algo);

Then the buffer can be a 'byte array', and after the values concatenation, the 
hash calculation can be called like:

gcry_md_write(hd, buffer,sizeof(buffer));
HB = gcry_md_read(hd,algo);

Could be this the way you said?



On Friday 02 January 2009 01:21:27 Sergi Blanch i Torné wrote:
> On Thursday 01 January 2009 20:44:01 Moritz Schulte wrote:
> > > What I don't know now is how to correctly create this 'context'?
> > > Everywhere this is a 'pointer to void', and I cannot read the how.
> >
> > Why are you trying to fiddle around with Libgcrypt internals instead of
> > using the exported programing interface as it is documented in the
> > manual?
> Yes, probably I am try from the wrong way. I'm writting in the libgcrypt
> the elliptic curve encrypt algorithm from the 'ECC in OpenPGP' internet
> draft. By the way this code is in, also I can write the methods from module
> to module as an external view.
> > Have a look at the manual and the included test programs.
> >
> > To answer your specific question about the origin of the hash context:
> > the gcry_md_spec_t structure contains the info about the required size
> > for the context buffer.  This is allocated in md.c and then initialized
> > with the algorithm-specific initialization function (also contained in
> > that struct).
> I found this, are you talking about the 'gcry_md_context' struct? You
> answer more than you think because I was declaring the buffer as a byte
> array, and it must be a gcry_md_hd_t? I'm checking it.
> > Hope that helps,
> > moritz
> To avoid future questions and wrong way coding I like to explain what I did
> by now. In the cipher/ecc.c, the interface methods ecc_encrypt and
> ecc_decrypt are add also with the 'gcry_pk_spec_t', 'pk_extra_spec_t' and
> the aliases. Internally also exists the encrypt and decrypt methods but
> some auxiliaries are need.
> From the standard I said a 'key derivation function' has to be implemented.
> Also in the document is explained, it comes from the Nist SP800-56A. Next
> step will be the AESkeyWrap (and the unwrap) from the rfc3394. But this
> will be further discussion.
> Using this moment, I like to prepare a patch that disturbs yous work at the
> minimum. Not like it was on ecdsa, when hundreds of things needs to be
> rewritten (not by me). Which communication can be the best?
> Really thanks!
> /Sergi.

“Success is not the key to happiness. Happiness is the key to success. If you 
love what you are doing, you will be successful” – Albert Schweitzer.

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