From bbbb95e869d8554cb66da787ab2e076caa680137 Mon Sep 17 00:00:00 2001
From: Joost Rijneveld <joost@joostrijneveld.nl>
Date: Tue, 24 Oct 2017 17:21:16 +0200
Subject: [PATCH] Fix erroneous index length for XMSSMT

This produced repeated indices when reaching 2^32 signatures.
This was introduced in 9b35b00d98d26feb3b58bcbc2c17c057d95efbda
with the re-introduction of runtime parameters. Compile-time parameters
did not contain this error.
---
 params.c    | 3 ++-
 xmss_core.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/params.c b/params.c
index f947e70..4e0f484 100644
--- a/params.c
+++ b/params.c
@@ -456,7 +456,8 @@ int xmssmt_parse_oid(xmss_params *params, const uint32_t oid)
     params->wots_len2 = 3;
     params->wots_len = params->wots_len1 + params->wots_len2;
     params->wots_keysize = params->wots_len * params->n;
-    params->index_len = 4;
+    /* Round index_len up to nearest byte. */
+    params->index_len = (params->full_height + 7) / 8;
     params->bytes = (params->index_len + params->n + params->d*params->wots_keysize
                      + params->full_height *params->n);
     params->publickey_bytes = 2*params->n;
diff --git a/xmss_core.c b/xmss_core.c
index d996233..2410d57 100644
--- a/xmss_core.c
+++ b/xmss_core.c
@@ -176,7 +176,7 @@ int xmssmt_core_keypair(const xmss_params *params,
 
     /* Initialize index to 0. */
     memset(sk, 0, params->index_len);
-    sk += 4;
+    sk += params->index_len;
 
     /* Initialize SK_SEED, SK_PRF and PUB_SEED. */
     randombytes(sk, 3 * params->n);