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Add comments trying to explain what bad things happen here, i.e.

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how hashed MD5/SHA are implemented, abusing Final() for padding and
sw_octx to transport the key from the beginning to the end.

Enlightened about what was going on here by: cperciva
Reviewed by:	cperciva
MFC After:	3 days
X-MFC with:	r187826
PR:		kern/126468
This commit is contained in:
Bjoern A. Zeeb 2010-01-09 15:43:47 +00:00
parent f1727e425a
commit 77680d964f
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=201898
1 changed files with 18 additions and 1 deletions
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19
sys/opencrypto/cryptosoft.c
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@ -434,7 +434,16 @@ swcr_authprepare(struct auth_hash *axf, struct swcr_data *sw, u_char *key,
case CRYPTO_MD5_KPDK:
case CRYPTO_SHA1_KPDK:
{
/* We need a buffer that can hold an md5 and a sha1 result. */
/*
* We need a buffer that can hold an md5 and a sha1 result
* just to throw it away.
* What we do here is the initial part of:
* ALGO( key, keyfill, .. )
* adding the key to sw_ictx and abusing Final() to get the
* "keyfill" padding.
* In addition we abuse the sw_octx to save the key to have
* it to be able to append it at the end in swcr_authcompute().
*/
u_char buf[SHA1_RESULTLEN];
sw->sw_klen = klen;
@ -495,9 +504,17 @@ swcr_authcompute(struct cryptodesc *crd, struct swcr_data *sw, caddr_t buf,
case CRYPTO_MD5_KPDK:
case CRYPTO_SHA1_KPDK:
/* If we have no key saved, return error. */
if (sw->sw_octx == NULL)
return EINVAL;
/*
* Add the trailing copy of the key (see comment in
* swcr_authprepare()) after the data:
* ALGO( .., key, algofill )
* and let Final() do the proper, natural "algofill"
* padding.
*/
axf->Update(&ctx, sw->sw_octx, sw->sw_klen);
axf->Final(aalg, &ctx);
break;