Import code from previous AssetBuilder version

thirdparty/libtomcrypt/pk/dh/dh_generate_key.c

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+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ */
+
+#include "tomcrypt.h"
+
+#ifdef LTC_MDH
+
+static int _dh_groupsize_to_keysize(int groupsize)
+{
+   /* The strength estimates from https://tools.ietf.org/html/rfc3526#section-8
+    * We use "Estimate 2" to get an appropriate private key (exponent) size.
+    */
+   if (groupsize <= 0) {
+      return 0;
+   }
+   else if (groupsize <= 192) {
+      return 30;     /* 1536-bit => key size 240-bit */
+   }
+   else if (groupsize <= 256) {
+      return 40;     /* 2048-bit => key size 320-bit */
+   }
+   else if (groupsize <= 384) {
+      return 52;     /* 3072-bit => key size 416-bit */
+   }
+   else if (groupsize <= 512) {
+      return 60;     /* 4096-bit => key size 480-bit */
+   }
+   else if (groupsize <= 768) {
+      return 67;     /* 6144-bit => key size 536-bit */
+   }
+   else if (groupsize <= 1024) {
+      return 77;     /* 8192-bit => key size 616-bit */
+   }
+   else {
+      return 0;
+   }
+}
+
+int dh_generate_key(prng_state *prng, int wprng, dh_key *key)
+{
+   unsigned char *buf;
+   unsigned long keysize;
+   int err, max_iterations = LTC_PK_MAX_RETRIES;
+
+   LTC_ARGCHK(key         != NULL);
+   LTC_ARGCHK(ltc_mp.name != NULL);
+
+   /* good prng? */
+   if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
+      return err;
+   }
+
+   keysize = _dh_groupsize_to_keysize(mp_unsigned_bin_size(key->prime));
+   if (keysize == 0) {
+      err = CRYPT_INVALID_KEYSIZE;
+      goto freemp;
+   }
+
+   /* allocate buffer */
+   buf = XMALLOC(keysize);
+   if (buf == NULL) {
+      err = CRYPT_MEM;
+      goto freemp;
+   }
+
+   key->type = PK_PRIVATE;
+   do {
+      /* make up random buf */
+      if (prng_descriptor[wprng].read(buf, keysize, prng) != keysize) {
+         err = CRYPT_ERROR_READPRNG;
+         goto freebuf;
+      }
+      /* load the x value - private key */
+      if ((err = mp_read_unsigned_bin(key->x, buf, keysize)) != CRYPT_OK) {
+         goto freebuf;
+      }
+      /* compute the y value - public key */
+      if ((err = mp_exptmod(key->base, key->x, key->prime, key->y)) != CRYPT_OK) {
+         goto freebuf;
+      }
+      err = dh_check_pubkey(key);
+   } while (err != CRYPT_OK && max_iterations-- > 0);
+
+freebuf:
+   zeromem(buf, keysize);
+   XFREE(buf);
+freemp:
+   if (err != CRYPT_OK) dh_free(key);
+   return err;
+}
+
+#endif /* LTC_MDH */
+
+/* ref:         HEAD -> master, tag: v1.18.2 */
+/* git commit:  7e7eb695d581782f04b24dc444cbfde86af59853 */
+/* commit time: 2018-07-01 22:49:01 +0200 */