crypto/shachain: enforce that indexes have to be added incrementally.

[ccan] / ccan / crypto / shachain / shachain.c

diff --git a/ccan/crypto/shachain/shachain.c b/ccan/crypto/shachain/shachain.c
index c66196f71d881ce5e19b9bc088d66b9d2fc8b03b..94d7d6466c0a05b4fdac6c57b9bcbc6f3b9b0f13 100644 (file)
--- a/ccan/crypto/shachain/shachain.c
+++ b/ccan/crypto/shachain/shachain.c
@@ -44,21 +44,34 @@ void shachain_from_seed(const struct sha256 *seed, shachain_index_t index,
        derive((shachain_index_t)-1ULL, index, seed, hash);
 }
 
-void shachain_init(struct shachain *shachain)
+void shachain_init(struct shachain *chain)
 {
-       shachain->num_valid = 0;
+       chain->num_valid = 0;
+       chain->max_index = 0;
 }
 
-void shachain_add_hash(struct shachain *chain,
+bool shachain_add_hash(struct shachain *chain,
                       shachain_index_t index, const struct sha256 *hash)
 {
        int i;
 
+       /* You have to insert them in order! */
+       assert(index == chain->max_index + 1 ||
+              (index == 0 && chain->num_valid == 0));
+       
        for (i = 0; i < chain->num_valid; i++) {
                /* If we could derive this value, we don't need it,
                 * not any others (since they're in order). */
-               if (can_derive(index, chain->known[i].index))
+               if (can_derive(index, chain->known[i].index)) {
+                       struct sha256 expect;
+
+                       /* Make sure the others derive as expected! */
+                       derive(index, chain->known[i].index, hash, &expect);
+                       if (memcmp(&expect, &chain->known[i].hash,
+                                  sizeof(expect)) != 0)
+                               return false;
                        break;
+               }
        }
 
        /* This can happen if you skip indices! */
@@ -66,6 +79,8 @@ void shachain_add_hash(struct shachain *chain,
        chain->known[i].index = index;
        chain->known[i].hash = *hash;
        chain->num_valid = i+1;
+       chain->max_index = index;
+       return true;
 }
 
 bool shachain_get_hash(const struct shachain *chain,