--- /dev/null
+../../../licenses/BSD-MIT
\ No newline at end of file
--- /dev/null
+#include "config.h"
+#include <stdio.h>
+#include <string.h>
+
+/**
+ * crypto/shachain - compactly-representable chain of 256-bit numbers.
+ *
+ * This code produces a practically infinite (2^64) chain of 256-bit numbers
+ * from a single number, such that you can't derive element N from any element
+ * less than N, but can efficiently derive element N from a limited number
+ * of elements >= N.
+ *
+ * License: BSD-MIT
+ * Author: Rusty Russell <rusty@rustcorp.com.au>
+ */
+int main(int argc, char *argv[])
+{
+ /* Expect exactly one argument */
+ if (argc != 2)
+ return 1;
+
+ if (strcmp(argv[1], "depends") == 0) {
+ printf("ccan/ilog\n");
+ printf("ccan/crypto/sha256\n");
+ return 0;
+ }
+
+ return 1;
+}
--- /dev/null
+/* MIT (BSD) license - see LICENSE file for details */
+#include <ccan/crypto/shachain/shachain.h>
+#include <ccan/ilog/ilog.h>
+#include <limits.h>
+#include <string.h>
+#include <assert.h>
+
+static void change_bit(unsigned char *arr, size_t index)
+{
+ arr[index / CHAR_BIT] ^= (1 << (index % CHAR_BIT));
+}
+
+static void derive(shachain_index_t index, size_t bits, struct sha256 *hash)
+{
+ int i;
+
+ for (i = bits - 1; i >= 0; i--) {
+ if (!((index >> i) & 1)) {
+ change_bit(hash->u.u8, i);
+ sha256(hash, hash, 1);
+ }
+ }
+}
+
+void shachain_from_seed(const struct sha256 *seed, shachain_index_t index,
+ struct sha256 *hash)
+{
+ *hash = *seed;
+ derive(index, sizeof(index) * CHAR_BIT, hash);
+}
+
+void shachain_init(struct shachain *shachain)
+{
+ shachain->num_valid = 0;
+}
+
+/* We can only ever *unset* bits, so to must only have bits in from. */
+static bool can_derive(shachain_index_t from, shachain_index_t to)
+{
+ return (~from & to) == 0;
+}
+
+void shachain_add_hash(struct shachain *chain,
+ shachain_index_t index, const struct sha256 *hash)
+{
+ int i;
+
+ 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))
+ break;
+ }
+
+ /* This can happen if you skip indices! */
+ assert(i < sizeof(chain->known) / sizeof(chain->known[0]));
+ chain->known[i].index = index;
+ chain->known[i].hash = *hash;
+ chain->num_valid = i+1;
+}
+
+bool shachain_get_hash(const struct shachain *chain,
+ shachain_index_t index, struct sha256 *hash)
+{
+ int i;
+
+ for (i = 0; i < chain->num_valid; i++) {
+ shachain_index_t diff;
+
+ /* If we can get from key to index only by resetting bits,
+ * we can derive from it => index has no bits key doesn't. */
+ if (!can_derive(chain->known[i].index, index))
+ continue;
+
+ /* Start from this hash. */
+ *hash = chain->known[i].hash;
+
+ /* This indicates the bits which are in 'index' and
+ * not the key */
+ diff = index ^ chain->known[i].index;
+
+ /* Using ilog64 here is an optimization. */
+ derive(~diff, ilog64(diff), hash);
+ return true;
+ }
+ return false;
+}
--- /dev/null
+/* MIT (BSD) license - see LICENSE file for details */
+#ifndef CCAN_CRYPTO_SHACHAIN_H
+#define CCAN_CRYPTO_SHACHAIN_H
+#include "config.h"
+#include <ccan/crypto/sha256/sha256.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+/* Useful for testing. */
+#ifndef shachain_index_t
+#define shachain_index_t uint64_t
+#endif
+
+void shachain_from_seed(const struct sha256 *seed, shachain_index_t index,
+ struct sha256 *hash);
+
+struct shachain {
+ unsigned int num_valid;
+ struct {
+ shachain_index_t index;
+ struct sha256 hash;
+ } known[sizeof(shachain_index_t) * 8];
+};
+
+void shachain_init(struct shachain *shachain);
+
+void shachain_add_hash(struct shachain *shachain,
+ shachain_index_t index, const struct sha256 *hash);
+
+bool shachain_get_hash(const struct shachain *shachain,
+ shachain_index_t index, struct sha256 *hash);
+#endif /* CCAN_CRYPTO_SHACHAIN_H */
--- /dev/null
+#define shachain_index_t uint8_t
+
+#include <ccan/crypto/shachain/shachain.h>
+/* Include the C files directly. */
+#include <ccan/crypto/shachain/shachain.c>
+#include <ccan/tap/tap.h>
+
+#include <stdio.h>
+
+#define NUM_TESTS 255
+
+int main(void)
+{
+ struct sha256 seed;
+ struct shachain chain;
+ struct sha256 expect[NUM_TESTS];
+ size_t i, j;
+
+ /* This is how many tests you plan to run */
+ plan_tests(NUM_TESTS + NUM_TESTS * (NUM_TESTS + 1) + NUM_TESTS);
+
+ memset(&seed, 0, sizeof(seed));
+ /* Generate a whole heap. */
+ for (i = 0; i < NUM_TESTS; i++) {
+ shachain_from_seed(&seed, i, &expect[i]);
+ if (i == 0)
+ ok1(memcmp(&expect[i], &seed, sizeof(expect[i])));
+ else
+ ok1(memcmp(&expect[i], &expect[i-1], sizeof(expect[i])));
+ }
+
+ shachain_init(&chain);
+
+ for (i = 0; i < NUM_TESTS; i++) {
+ struct sha256 hash;
+
+ shachain_add_hash(&chain, i, &expect[i]);
+ for (j = 0; j <= i; j++) {
+ ok1(shachain_get_hash(&chain, j, &hash));
+ ok1(memcmp(&hash, &expect[j], sizeof(hash)) == 0);
+ }
+ ok1(!shachain_get_hash(&chain, i+1, &hash));
+ if (chain.num_valid == 8) {
+ printf("%zu: num_valid %u\n", i, chain.num_valid);
+ for (j = 0; j < 8; j++)
+ printf("chain.known[%zu] = 0x%02x\n",
+ j, chain.known[j].index);
+ }
+ }
+
+ return exit_status();
+}
--- /dev/null
+#include <ccan/crypto/shachain/shachain.h>
+/* Include the C files directly. */
+#include <ccan/crypto/shachain/shachain.c>
+#include <ccan/tap/tap.h>
+
+#define NUM_TESTS 50
+
+int main(void)
+{
+ struct sha256 seed;
+ struct shachain chain;
+ struct sha256 expect[NUM_TESTS];
+ size_t i, j;
+
+ /* This is how many tests you plan to run */
+ plan_tests(NUM_TESTS + NUM_TESTS * (NUM_TESTS + 1) + NUM_TESTS);
+
+ memset(&seed, 0, sizeof(seed));
+ /* Generate a whole heap. */
+ for (i = 0; i < NUM_TESTS; i++) {
+ shachain_from_seed(&seed, i, &expect[i]);
+ if (i == 0)
+ ok1(memcmp(&expect[i], &seed, sizeof(expect[i])));
+ else
+ ok1(memcmp(&expect[i], &expect[i-1], sizeof(expect[i])));
+ }
+
+ shachain_init(&chain);
+
+ for (i = 0; i < NUM_TESTS; i++) {
+ struct sha256 hash;
+
+ shachain_add_hash(&chain, i, &expect[i]);
+ for (j = 0; j <= i; j++) {
+ ok1(shachain_get_hash(&chain, j, &hash));
+ ok1(memcmp(&hash, &expect[j], sizeof(hash)) == 0);
+ }
+ ok1(!shachain_get_hash(&chain, i+1, &hash));
+ }
+
+ return exit_status();
+}