crypto/shachain: new module

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/ccan/crypto/shachain/LICENSE b/ccan/crypto/shachain/LICENSE
new file mode 120000 (symlink)
index 0000000..2b1feca
--- /dev/null
+++ b/ccan/crypto/shachain/LICENSE
@@ -0,0 +1 @@
+../../../licenses/BSD-MIT
\ No newline at end of file

diff --git a/ccan/crypto/shachain/_info b/ccan/crypto/shachain/_info
new file mode 100644 (file)
index 0000000..7cbf02d
--- /dev/null
+++ b/ccan/crypto/shachain/_info
@@ -0,0 +1,29 @@
+#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;
+}

diff --git a/ccan/crypto/shachain/shachain.c b/ccan/crypto/shachain/shachain.c
new file mode 100644 (file)
index 0000000..4b6a31d
--- /dev/null
+++ b/ccan/crypto/shachain/shachain.c
@@ -0,0 +1,87 @@
+/* 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;
+}

diff --git a/ccan/crypto/shachain/shachain.h b/ccan/crypto/shachain/shachain.h
new file mode 100644 (file)
index 0000000..b0f947e
--- /dev/null
+++ b/ccan/crypto/shachain/shachain.h
@@ -0,0 +1,32 @@
+/* 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 */

diff --git a/ccan/crypto/shachain/test/run-8bit.c b/ccan/crypto/shachain/test/run-8bit.c
new file mode 100644 (file)
index 0000000..10520bc
--- /dev/null
+++ b/ccan/crypto/shachain/test/run-8bit.c
@@ -0,0 +1,52 @@
+#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();
+}

diff --git a/ccan/crypto/shachain/test/run.c b/ccan/crypto/shachain/test/run.c
new file mode 100644 (file)
index 0000000..3939168
--- /dev/null
+++ b/ccan/crypto/shachain/test/run.c
@@ -0,0 +1,42 @@
+#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();
+}