Tim Ruehsen <[email protected]> writes:
> I meanwhile found the nettle docs on the web
> (http://www.lysator.liu.se/~nisse/nettle/nettle.html#MD5):
I'm happy you found the documentation. The manual should also be
included in debian's nettle-dev package, in info, html and pdf formats.
> ###########
> Function: void md5_digest (struct md5_ctx *ctx, size_t length, uint8_t
> *digest)
>
> Performs final processing and extracts the message digest, writing it to
> digest. length may be smaller than MD5_DIGEST_SIZE, in which case only the
> first length octets of the digest are written.
> ###########
Sorry you find this unclear. Can you suggest a concise improvement?
> unsigned char digest[128]; // *should* be large enough, if not we get an error
> char *algo = <user input>
> if ((len=hash(algo,text,textlen,digest,digestsize)) < 0) {
> // error like 'unknown algo', 'digest size too small', ...
> } else {
> // got <len> bytes in digest, e.g. print as hex values
> }
For simplicity, let's assume that algoriths are represented by struct
nettle_hash, rather than an ascii name. Then a hash function
in that style should be implemented like
int hash (const struct nettle_hash *hash,
const uint8_t *msg, size_t length,
uint8_t *digest, size_t digest_size)
{
void *ctx;
if (digest_size < hash->digest_size)
/* Too small */
return -1;
ctx = alloca(hash->context_size);
hash->init(ctx);
hash->update(ctx, length, msg);
hash->digest(ctx, hash->digest_size, digest);
return hash->digest_size;
}
I don't think that passing a valid digest size to hash->digest here
should be a big deal.
Regards,
/Niels
--
Niels Möller. PGP-encrypted email is preferred. Keyid C0B98E26.
Internet email is subject to wholesale government surveillance.
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