Comments and tweaks based on review by asn

Add some documentation

Rename "derive" -> "blind"

Check for failure on randombytes().

src/common/crypto_curve25519.c

@@ -128,7 +128,13 @@ curve25519_keypair_generate(curve25519_keypair_t *keypair_out,
   return 0;
 }
 
-/** DOCDOC */
+/** Write the <b>datalen</b> bytes from <b>data</b> to the file named
+ * <b>fname</b> in the tagged-data format.  This format contains a
+ * 32-byte header, followed by the data itself.  The header is the
+ * NUL-padded string "== <b>typestring</b>: <b>tag</b> ==".  The length
+ * of <b>typestring</b> and <b>tag</b> must therefore be no more than
+ * 24.
+ **/
 int
 crypto_write_tagged_contents_to_file(const char *fname,
                                      const char *typestring,
@@ -159,7 +165,11 @@ crypto_write_tagged_contents_to_file(const char *fname,
   return r;
 }
 
-/** DOCDOC */
+/** Read a tagged-data file from <b>fname</b> into the
+ * <b>data_out_len</b>-byte buffer in <b>data_out</b>. Check that the
+ * typestring matches <b>typestring</b>; store the tag into a newly allocated
+ * string in <b>tag_out</b>. Return -1 on failure, and the number of bytes of
+ * data on success. */
 ssize_t
 crypto_read_tagged_contents_from_file(const char *fname,
                                       const char *typestring,

src/common/crypto_ed25519.c

@@ -138,6 +138,8 @@ ed25519_checksig_batch(int *okay_out,
   }
 
 #if 0
+  /* This is how we'd do it if we were using ed25519_donna.  I'll keep this
+   * code around here in case we ever do that. */
   const uint8_t **ms;
   size_t *lens;
   const uint8_t **pks;
@@ -249,7 +251,7 @@ ed25519_keypair_blind(ed25519_keypair_t *out,
 {
   ed25519_public_key_t pubkey_check;
 
-  ed25519_ref10_derive_secret_key(out->seckey.seckey,
+  ed25519_ref10_blind_secret_key(out->seckey.seckey,
                                   inp->seckey.seckey, param);
 
   ed25519_public_blind(&pubkey_check, &inp->pubkey, param);
@@ -272,7 +274,7 @@ ed25519_public_blind(ed25519_public_key_t *out,
                      const ed25519_public_key_t *inp,
                      const uint8_t *param)
 {
-  ed25519_ref10_derive_public_key(out->pubkey, inp->pubkey, param);
+  ed25519_ref10_blind_public_key(out->pubkey, inp->pubkey, param);
   return 0;
 }