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Re: Adding sha256 and sha512 to C?
From: |
Paul Eggert |
Subject: |
Re: Adding sha256 and sha512 to C? |
Date: |
Sun, 12 Jun 2011 15:37:39 -0700 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.17) Gecko/20110516 Thunderbird/3.1.10 |
On 06/12/11 06:03, Leo wrote:
> (sha OBJECT &optional START END BINARY ALGORITHM)
>
> where ALGORITHM can be 1 (default), 224, 256, 384, 512, and make sha1
> obsolete? In a sense we unify all SHA functions and leave MD5 as is.
That's better, thanks, but I still have two qualms. First, the name
"sha" is confusing at the Emacs Lisp level: it feels too much like
"ash". It's not like programmers will be using crypto functions in
every expression; their names need not be *that* short. How about the
name "secure-hash" instead? That's pretty short.
Second, naming algorithms via bit counts doesn't sound
forward-looking. SHA-3 is likely to have a 512-bit variant, for
example. How about using atoms to name the algorithms, e.g., SHA-1,
SHA-224, SHA-256, etc.? This is more likely to be robust after SHA-3
comes out, not to mention SHA-4 etc.
+ hash_func = &md5_buffer;
There's no need for the "&" here, or in similar assignments to
hash_func. (And there's no need for multiple spaces before the "=".)
+ digest = make_uninit_string (digest_size);
...
+ Lisp_Object value = make_uninit_string (2 * digest_size);
There's no need to call make_uninit_string twice, as only one
string is being returned. Any temporary buffer for the digest can
be put into the C stack. Or, perhaps better, use the same
uninitialized string for both the binary digest and the text
digest, and run the binary-to-text loop backwards (and without
using sprintf) so that the loop doesn't stomp on its own work.
Something like this:
unsigned char *p = SDATA (digest);
for (i = digest_size - 1; i >= 0; i--)
{
static char const hexdigit[16] = "0123456789abcdef";
int p_i = p[i];
p[2 * i] = hexdigit[p_i >> 4];
p[2 * i + 1] = hexdigit[p_i & 0xf];
}
The text-vs-binary checksum thing seems to be enough of a hassle that
perhaps it should be pulled out into a separate function, rather than
as a flag to the sha/secure-hash function. That is, secure-hash could
always return the text form, and if someone wants a binary form they
could call the text-to-binary converter.
Won't there need to be changes to the Emacs Lisp reference manual, and
to NEWS?
- Re: Adding sha256 and sha512 to C?, (continued)
- Re: Adding sha256 and sha512 to C?, Eli Zaretskii, 2011/06/11
- Re: Adding sha256 and sha512 to C?, Leo, 2011/06/11
- Re: Adding sha256 and sha512 to C?, Eli Zaretskii, 2011/06/11
- Re: Adding sha256 and sha512 to C?, Paul Eggert, 2011/06/11
- Re: Adding sha256 and sha512 to C?, Juanma Barranquero, 2011/06/11
- Re: Adding sha256 and sha512 to C?, YAMAMOTO Mitsuharu, 2011/06/11
- Re: Adding sha256 and sha512 to C?, Leo, 2011/06/12
- Re: Adding sha256 and sha512 to C?, Thien-Thi Nguyen, 2011/06/12
- Re: Adding sha256 and sha512 to C?, Deniz Dogan, 2011/06/12
- Re: Adding sha256 and sha512 to C?, Richard Riley, 2011/06/12
- Re: Adding sha256 and sha512 to C?,
Paul Eggert <=
- Re: Adding sha256 and sha512 to C?, Leo, 2011/06/19