From 35dbc26221aed90ba05e6d0e57c8f280f9f4be91 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Niels=20M=C3=B6ller?= <nisse@lysator.liu.se>
Date: Sun, 14 Oct 2001 22:25:57 +0200
Subject: [PATCH] * yarrow256.c (YARROW_RESEED_ITERATIONS): New constant.
(yarrow_iterate): New function. (yarrow_fast_reseed): Call yarrow_iterate.
Rev: src/nettle/yarrow256.c:1.9
---
yarrow256.c | 45 +++++++++++++++++++++++++++++++++++++++++----
1 file changed, 41 insertions(+), 4 deletions(-)
diff --git a/yarrow256.c b/yarrow256.c
index bef0a9ee..3b31bf68 100644
--- a/yarrow256.c
+++ b/yarrow256.c
@@ -25,6 +25,8 @@
#include "yarrow.h"
+#include "macros.h"
+
#include <assert.h>
#include <string.h>
@@ -48,6 +50,11 @@
/* Number of sources that must exceed the threshold for slow reseed */
#define YARROW_SLOW_K 2
+/* The number of iterations when reseeding, P_t in the yarrow paper.
+ * Should be chosen so that reseeding takes on the order of 0.1-1
+ * seconds. */
+#define YARROW_RESEED_ITERATIONS 1500
+
/* Entropy estimates sticks to this value, it is treated as infinity
* in calculations. It should fit comfortably in an uint32_t, to avoid
* overflows. */
@@ -97,16 +104,43 @@ yarrow_generate_block(struct yarrow256_ctx *ctx,
}
}
+static void
+yarrow_iterate(uint8_t *digest)
+{
+ uint8_t v0[SHA256_DIGEST_SIZE];
+ unsigned i;
+
+ memcpy(v0, digest, SHA256_DIGEST_SIZE);
+
+ /* When hashed inside the loop, i should run from 1 to
+ * YARROW_RESEED_ITERATIONS */
+ for (i = 0; ++i < YARROW_RESEED_ITERATIONS; )
+ {
+ uint8_t count[4];
+ struct sha256_ctx hash;
+
+ sha256_init(&hash);
+
+ /* Hash v_i | v_0 | i */
+ WRITE_UINT32(count, i);
+ sha256_update(&hash, SHA256_DIGEST_SIZE, digest);
+ sha256_update(&hash, sizeof(v0), v0);
+ sha256_update(&hash, sizeof(count), count);
+
+ sha256_final(&hash);
+ sha256_digest(&hash, SHA256_DIGEST_SIZE, digest);
+ }
+}
+
/* NOTE: The SHA-256 digest size equals the AES key size, so we need
- * no "size adaptor". We also use P_t = 0, i.e. we don't currently try
- * to make reseeding computationally expensive. */
+ * no "size adaptor". */
static void
yarrow_fast_reseed(struct yarrow256_ctx *ctx)
{
uint8_t digest[SHA256_DIGEST_SIZE];
unsigned i;
-
+
#ifdef YARROW_DEBUG
fprintf(stderr, "yarrow_fast_reseed\n");
#endif
@@ -125,7 +159,10 @@ yarrow_fast_reseed(struct yarrow256_ctx *ctx)
sha256_final(&ctx->pools[YARROW_FAST]);
sha256_digest(&ctx->pools[YARROW_FAST], sizeof(digest), digest);
sha256_init(&ctx->pools[YARROW_FAST]);
-
+
+ /* Iterate */
+ yarrow_iterate(digest);
+
aes_set_key(&ctx->key, sizeof(digest), digest);
/* Derive new counter value */
--
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