*
* License: BSD-MIT
* Author: Rusty Russell <rusty@rustcorp.com.au>
+ *
+ * Example:
+ *
+ * #include <ccan/crypto/shachain/shachain.h>
+ * #include <ccan/err/err.h>
+ * #include <stdio.h>
+ * #include <stdlib.h>
+ * #include <string.h>
+ *
+ * int main(int argc, char *argv[])
+ * {
+ * size_t i, j, limit = 10;
+ * struct sha256 seed;
+ *
+ * if (argc < 2)
+ * errx(1, "Usage: %s <passphrase> [<num-to-generate>]", argv[0]);
+ * sha256(&seed, argv[1], strlen(argv[1]));
+ * if (argv[2])
+ * limit = atol(argv[2]);
+ *
+ * for (i = 0; i < limit; i++) {
+ * struct sha256 v;
+ * shachain_from_seed(&seed, i, &v);
+ * printf("%zu: ", i);
+ * for (j = 0; j < sizeof(v.u.u8); j++)
+ * printf("%02x", v.u.u8[j]);
+ * printf("\n");
+ * }
+ * return 0;
+ * }
*/
int main(int argc, char *argv[])
{
#define shachain_index_t uint64_t
#endif
+/**
+ * shachain_from_seed - Generate an unpredictable SHA from a seed value.
+ * @seed: (secret) seed value to use
+ * @index: index of value to generate.
+ * @hash: value generated
+ *
+ * There will be no way to derive the result from that generated for
+ * any *lesser* index.
+ *
+ * Example:
+ * #include <time.h>
+ *
+ * static void next_hash(struct sha256 *hash)
+ * {
+ * static uint64_t index = 0;
+ * static struct sha256 seed;
+ *
+ * // First time, initialize seed.
+ * if (index == 0) {
+ * // DO NOT DO THIS! Very predictable!
+ * time_t now = time(NULL);
+ * memcpy(&seed, &now, sizeof(now));
+ * }
+ *
+ * shachain_from_seed(&seed, index++, hash);
+ * }
+ */
void shachain_from_seed(const struct sha256 *seed, shachain_index_t index,
struct sha256 *hash);
+/**
+ * shachain - structure for recording/deriving incrementing chain members
+ * @max_index: maximum index value successfully shachain_add_hash()ed.
+ * @num_valid: number of known[] array valid. If non-zero, @max_index valid.
+ * @known: known values to allow us to derive those <= @max_index.
+ *
+ * This is sufficient storage to derive any shachain hash value previously
+ * added.
+ */
struct shachain {
shachain_index_t max_index;
unsigned int num_valid;
} known[sizeof(shachain_index_t) * 8];
};
-void shachain_init(struct shachain *shachain);
+/**
+ * shachain_init - initialize an shachain
+ * @chain: the chain to initialize
+ *
+ * Alternately, ensure that it's all zero.
+ */
+void shachain_init(struct shachain *chain);
-bool shachain_add_hash(struct shachain *shachain,
+/**
+ * shachain_add_hash - record the hash for the next index.
+ * @chain: the chain to add to
+ * @index: the index of the hash
+ * @hash: the hash value.
+ *
+ * You can only add index 0 (for a freshly initialized chain), or one more
+ * than the previously successfully added value.
+ *
+ * This can fail (return false without altering @chain) if the hash
+ * for this index isn't consistent with previous hashes (ie. wasn't
+ * generated from the same seed), though it can't always detect that.
+ * If the hash is inconsistent yet undetected, the next addition will
+ * fail.
+ *
+ * Example:
+ * static void next_hash(const struct sha256 *hash)
+ * {
+ * static uint64_t index = 0;
+ * static struct shachain chain;
+ *
+ * if (!shachain_add_hash(&chain, index++, hash))
+ * errx(1, "Corrupted hash value?");
+ * }
+ */
+bool shachain_add_hash(struct shachain *chain,
shachain_index_t index, const struct sha256 *hash);
-bool shachain_get_hash(const struct shachain *shachain,
+/**
+ * shachain_get_hash - get the hash for a given index.
+ * @chain: the chain query
+ * @index: the index of the hash to get
+ * @hash: the hash value.
+ *
+ * This will return true and set @hash to that given in the successful
+ * shachain_get_hash() call for that index. If there was no
+ * successful shachain_get_hash() for that index, it will return
+ * false.
+ *
+ * Example:
+ * #include <ccan/structeq/structeq.h>
+ *
+ * static void next_hash(const struct sha256 *hash)
+ * {
+ * static uint64_t index = 0;
+ * static struct shachain chain;
+ *
+ * if (!shachain_add_hash(&chain, index++, hash))
+ * errx(1, "Corrupted hash value?");
+ * else {
+ * struct sha256 check;
+ * assert(shachain_get_hash(&chain, index-1, &check));
+ * assert(structeq(&check, hash));
+ * }
+ * }
+ */
+bool shachain_get_hash(const struct shachain *chain,
shachain_index_t index, struct sha256 *hash);
#endif /* CCAN_CRYPTO_SHACHAIN_H */