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authorStephan Mueller <smueller@chronox.de>2014-07-06 02:24:35 +0200
committerHerbert Xu <herbert@gondor.apana.org.au>2014-07-08 21:18:24 +0800
commit72e7c25aa6d73df2951229d2ce0a35065de66d3a (patch)
tree5d242f50c32207d375766ca579b375f30fbb42a8 /crypto
parenta9089571f2fc203c3ba6595a60f0045f048494da (diff)
downloadlinux-stericsson-72e7c25aa6d73df2951229d2ce0a35065de66d3a.tar.gz
crypto: drbg - Call CTR DRBG DF function only once
The CTR DRBG requires the update function to be called twice when generating a random number. In both cases, update function must process the additional information string by using the DF function. As the DF produces the same result in both cases, we can save one invocation of the DF function when the first DF function result is reused. The result of the DF function is stored in the scratchpad storage. The patch ensures that the scratchpad is not cleared when we want to reuse the DF result. For achieving this, the CTR DRBG update function must know by whom and in which scenario it is called. This information is provided with the reseed parameter to the update function. Signed-off-by: Stephan Mueller <smueller@chronox.de> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'crypto')
-rw-r--r--crypto/drbg.c41
1 files changed, 22 insertions, 19 deletions
diff --git a/crypto/drbg.c b/crypto/drbg.c
index c9b4c4906d9b..dba5ed2f83b6 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -562,7 +562,21 @@ out:
return ret;
}
-/* update function of CTR DRBG as defined in 10.2.1.2 */
+/*
+ * update function of CTR DRBG as defined in 10.2.1.2
+ *
+ * The reseed variable has an enhanced meaning compared to the update
+ * functions of the other DRBGs as follows:
+ * 0 => initial seed from initialization
+ * 1 => reseed via drbg_seed
+ * 2 => first invocation from drbg_ctr_update when addtl is present. In
+ * this case, the df_data scratchpad is not deleted so that it is
+ * available for another calls to prevent calling the DF function
+ * again.
+ * 3 => second invocation from drbg_ctr_update. When the update function
+ * was called with addtl, the df_data memory already contains the
+ * DFed addtl information and we do not need to call DF again.
+ */
static int drbg_ctr_update(struct drbg_state *drbg, struct list_head *seed,
int reseed)
{
@@ -577,7 +591,8 @@ static int drbg_ctr_update(struct drbg_state *drbg, struct list_head *seed,
unsigned char prefix = DRBG_PREFIX1;
memset(temp, 0, drbg_statelen(drbg) + drbg_blocklen(drbg));
- memset(df_data, 0, drbg_statelen(drbg));
+ if (3 > reseed)
+ memset(df_data, 0, drbg_statelen(drbg));
/* 10.2.1.3.2 step 2 and 10.2.1.4.2 step 2 */
if (seed) {
@@ -619,7 +634,8 @@ static int drbg_ctr_update(struct drbg_state *drbg, struct list_head *seed,
out:
memset(temp, 0, drbg_statelen(drbg) + drbg_blocklen(drbg));
- memset(df_data, 0, drbg_statelen(drbg));
+ if (2 != reseed)
+ memset(df_data, 0, drbg_statelen(drbg));
return ret;
}
@@ -644,7 +660,7 @@ static int drbg_ctr_generate(struct drbg_state *drbg,
LIST_HEAD(addtllist);
list_add_tail(&addtl->list, &addtllist);
- ret = drbg_ctr_update(drbg, &addtllist, 1);
+ ret = drbg_ctr_update(drbg, &addtllist, 2);
if (ret)
return 0;
}
@@ -675,21 +691,8 @@ static int drbg_ctr_generate(struct drbg_state *drbg,
drbg_add_buf(drbg->V, drbg_blocklen(drbg), &prefix, 1);
}
- /*
- * 10.2.1.5.2 step 6
- * The following call invokes the DF function again which could be
- * optimized. In step 2, the "additional_input" after step 2 is the
- * output of the DF function. If this result would be saved, the DF
- * function would not need to be invoked again at this point.
- */
- if (addtl && 0 < addtl->len) {
- LIST_HEAD(addtllist);
-
- list_add_tail(&addtl->list, &addtllist);
- ret = drbg_ctr_update(drbg, &addtllist, 1);
- } else {
- ret = drbg_ctr_update(drbg, NULL, 1);
- }
+ /* 10.2.1.5.2 step 6 */
+ ret = drbg_ctr_update(drbg, NULL, 3);
if (ret)
len = ret;