--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/misc/hkdf/hkdf.c	Fri Feb 09 21:44:05 2018 +0800
@@ -0,0 +1,143 @@
+/* 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 <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "tomcrypt.h"
+
+#ifdef LTC_HKDF
+
+/* This is mostly just a wrapper around hmac_memory */
+int hkdf_extract(int hash_idx, const unsigned char *salt, unsigned long  saltlen,
+                               const unsigned char *in,   unsigned long  inlen,
+                                     unsigned char *out,  unsigned long *outlen)
+{
+   /* libtomcrypt chokes on a zero length HMAC key, so we need to check for
+      that.  HMAC specifies that keys shorter than the hash's blocksize are
+      0 padded to the block size.  HKDF specifies that a NULL salt is to be
+      substituted with a salt comprised of hashLen 0 bytes.  HMAC's padding
+      means that in either case the HMAC is actually using a blocksize long
+      zero filled key.  Unless blocksize < hashLen (which wouldn't make any
+      sense), we can use a single 0 byte as the HMAC key and still generate
+      valid results for HKDF. */
+   if (salt == NULL || saltlen == 0) {
+      return hmac_memory(hash_idx, (const unsigned char *)"",   1,       in, inlen, out, outlen);
+   } else {
+      return hmac_memory(hash_idx, salt, saltlen, in, inlen, out, outlen);
+   }
+}
+
+int hkdf_expand(int hash_idx, const unsigned char *info, unsigned long infolen,
+                              const unsigned char *in,   unsigned long inlen,
+                                    unsigned char *out,  unsigned long outlen)
+{
+   unsigned long hashsize;
+   int err;
+   unsigned char N;
+   unsigned long Noutlen, outoff;
+
+   unsigned char *T,  *dat;
+   unsigned long Tlen, datlen;
+
+   /* make sure hash descriptor is valid */
+   if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
+      return err;
+   }
+
+   hashsize = hash_descriptor[hash_idx].hashsize;
+
+   /* RFC5869 parameter restrictions */
+   if (inlen < hashsize || outlen > hashsize * 255)
+      return CRYPT_INVALID_ARG;
+   if (info == NULL && infolen != 0)
+      return CRYPT_INVALID_ARG;
+   LTC_ARGCHK(out != NULL);
+
+   Tlen = hashsize + infolen + 1;
+   T = XMALLOC(Tlen); /* Replace with static buffer? */
+   if (T == NULL) {
+      return CRYPT_MEM;
+   }
+   if (info != NULL) {
+      XMEMCPY(T + hashsize, info, infolen);
+   }
+
+   /* HMAC data T(1) doesn't include a previous hash value */
+   dat    = T    + hashsize;
+   datlen = Tlen - hashsize;
+
+   N = 0;
+   outoff = 0; /* offset in out to write to */
+   while (1) { /* an exit condition breaks mid-loop */
+      Noutlen = MIN(hashsize, outlen - outoff);
+      T[Tlen - 1] = ++N;
+      if ((err = hmac_memory(hash_idx, in, inlen, dat, datlen,
+                             out + outoff, &Noutlen)) != CRYPT_OK) {
+         zeromem(T, Tlen);
+         XFREE(T);
+         return err;
+      }
+      outoff += Noutlen;
+
+      if (outoff >= outlen) /* loop exit condition */
+         break;
+
+      /* All subsequent HMAC data T(N) DOES include the previous hash value */
+      XMEMCPY(T, out + hashsize * (N-1), hashsize);
+      if (N == 1) {
+         dat = T;
+         datlen = Tlen;
+      }
+   }
+   zeromem(T, Tlen);
+   XFREE(T);
+   return CRYPT_OK;
+}
+
+/* all in one step */
+int hkdf(int hash_idx, const unsigned char *salt, unsigned long saltlen,
+                       const unsigned char *info, unsigned long infolen,
+                       const unsigned char *in,   unsigned long inlen,
+                             unsigned char *out,  unsigned long outlen)
+{
+   unsigned long hashsize;
+   int err;
+   unsigned char *extracted;
+
+   /* make sure hash descriptor is valid */
+   if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
+      return err;
+   }
+
+   hashsize = hash_descriptor[hash_idx].hashsize;
+
+   extracted = XMALLOC(hashsize); /* replace with static buffer? */
+   if (extracted == NULL) {
+      return CRYPT_MEM;
+   }
+   if ((err = hkdf_extract(hash_idx, salt, saltlen, in, inlen, extracted, &hashsize)) != 0) {
+      zeromem(extracted, hashsize);
+      XFREE(extracted);
+      return err;
+   }
+   err = hkdf_expand(hash_idx, info, infolen, extracted, hashsize, out, outlen);
+   zeromem(extracted, hashsize);
+   XFREE(extracted);
+   return err;
+}
+#endif /* LTC_HKDF */
+
+
+/* vim: set ts=2 sw=2 et ai si: */
+
+/* ref:         $Format:%D$ */
+/* git commit:  $Format:%H$ */
+/* commit time: $Format:%ai$ */