Update chacha-poly1305 for draft-irtf-cfrg-chacha20-poly1305-08.

ChangeLog

 2015-01-30  Niels Möller  <nisse@lysator.liu.se>
 
+	Update chacha-poly1305 for draft-irtf-cfrg-chacha20-poly1305-08.
+	* chacha-poly1305.h (CHACHA_POLY1305_NONCE_SIZE): Increase to 12
+	bytes, i.e., CHACHA_NONCE96_SIZE.
+	* chacha-poly1305.c (chacha_poly1305_set_nonce): Use
+	chacha_set_nonce96.
+	(poly1305_pad): New function.
+	(chacha_poly1305_encrypt): Use poly1305_pad.
+	(chacha_poly1305_digest): Call poly1305_pad, and format length
+	fields as a single poly1305 block.
+
 	* chacha-set-nonce.c (chacha_set_nonce96): New function.
 	* chacha.h (CHACHA_NONCE96_SIZE): New constant.
 	* testsuite/chacha-test.c: Add test for chacha with 96-bit nonce.

chacha-poly1305.c

@@ -2,7 +2,7 @@
 
    AEAD mechanism based on chacha and poly1305.
 
-   Copyright (C) 2014 Niels Möller
+   Copyright (C) 2014, 2015 Niels Möller
 
    This file is part of GNU Nettle.
 
@@ -31,6 +31,20 @@
    not, see http://www.gnu.org/licenses/.
 */
 
+/* This implements chacha-poly1305 according to
+   draft-irtf-cfrg-chacha20-poly1305-08. The inputs to poly1305 are:
+
+     associated data
+     zero padding
+     ciphertext
+     zero padding
+     length of associated data (64-bit, little endian)
+     length of ciphertext (64-bit, little endian)
+
+   where the padding fields are 0-15 zero bytes, filling up to a
+   16-byte boundary.
+*/
+
 #if HAVE_CONFIG_H
 # include "config.h"
 #endif
@@ -62,7 +76,7 @@ chacha_poly1305_set_nonce (struct chacha_poly1305_ctx *ctx,
     uint8_t subkey[32];
   } u;
 
-  chacha_set_nonce (&ctx->chacha, nonce);
+  chacha_set_nonce96 (&ctx->chacha, nonce);
   /* Generate authentication key */
   _chacha_core (u.x, ctx->chacha.state, CHACHA_ROUNDS);
   poly1305_set_key (&ctx->poly1305, u.subkey);  
@@ -84,6 +98,17 @@ poly1305_update (struct chacha_poly1305_ctx *ctx,
   MD_UPDATE (ctx, length, data, COMPRESS, (void) 0);
 }
 
+static void
+poly1305_pad (struct chacha_poly1305_ctx *ctx)
+{
+  if (ctx->index)
+    {
+      memset (ctx->block + ctx->index, 0,
+	      POLY1305_BLOCK_SIZE - ctx->index);
+      _poly1305_block(&ctx->poly1305, ctx->block, 1);
+      ctx->index = 0;
+    }
+}
 void
 chacha_poly1305_update (struct chacha_poly1305_ctx *ctx,
 			size_t length, const uint8_t *data)
@@ -102,12 +127,8 @@ chacha_poly1305_encrypt (struct chacha_poly1305_ctx *ctx,
     return;
 
   assert (ctx->data_size % CHACHA_POLY1305_BLOCK_SIZE == 0);
-  if (!ctx->data_size)
-    {
-      uint8_t buf[8];
-      LE_WRITE_UINT64 (buf, ctx->auth_size);
-      poly1305_update (ctx, sizeof(buf), buf);
-    }
+  poly1305_pad (ctx);
+
   chacha_crypt (&ctx->chacha, length, dst, src);
   poly1305_update (ctx, length, dst);
   ctx->data_size += length;
@@ -121,12 +142,8 @@ chacha_poly1305_decrypt (struct chacha_poly1305_ctx *ctx,
     return;
 
   assert (ctx->data_size % CHACHA_POLY1305_BLOCK_SIZE == 0);
-  if (!ctx->data_size)
-    {
-      uint8_t buf[8];
-      LE_WRITE_UINT64 (buf, ctx->auth_size);
-      poly1305_update (ctx, sizeof(buf), buf);
-    }
+  poly1305_pad (ctx);
+
   poly1305_update (ctx, length, src);
   chacha_crypt (&ctx->chacha, length, dst, src);
   ctx->data_size += length;
@@ -136,27 +153,14 @@ void
 chacha_poly1305_digest (struct chacha_poly1305_ctx *ctx,
 			size_t length, uint8_t *digest)
 {
-  uint8_t buf[8];
-  if (!ctx->data_size)
-    {
-      LE_WRITE_UINT64 (buf, ctx->auth_size);
-      poly1305_update (ctx, sizeof(buf), buf);
-    }
-  LE_WRITE_UINT64 (buf, ctx->data_size);
-  poly1305_update (ctx, sizeof(buf), buf);
+  uint8_t buf[16];
 
-  /* Final bytes. FIXME: Duplicated in poly1305_aes128.c */
-  if (ctx->index > 0)
-    {
-      assert (ctx->index < POLY1305_BLOCK_SIZE);
+  poly1305_pad (ctx);
+  LE_WRITE_UINT64 (buf, ctx->auth_size);
+  LE_WRITE_UINT64 (buf + 8, ctx->data_size);
 
-      ctx->block[ctx->index] = 1;
-      memset (ctx->block + ctx->index + 1,
-	      0, POLY1305_BLOCK_SIZE - 1 - ctx->index);
+  _poly1305_block (&ctx->poly1305, buf, 1);
 
-      _poly1305_block (&ctx->poly1305, ctx->block, 0);
-    }
-  
   poly1305_digest (&ctx->poly1305, &ctx->s);
   memcpy (digest, &ctx->s.b, length);
 }

chacha-poly1305.h

@@ -53,7 +53,7 @@ extern "C" {
 #define CHACHA_POLY1305_BLOCK_SIZE 64
 /* FIXME: Any need for 128-bit variant? */
 #define CHACHA_POLY1305_KEY_SIZE 32
-#define CHACHA_POLY1305_NONCE_SIZE CHACHA_NONCE_SIZE
+#define CHACHA_POLY1305_NONCE_SIZE CHACHA_NONCE96_SIZE
 #define CHACHA_POLY1305_DIGEST_SIZE 16
 
 struct chacha_poly1305_ctx

testsuite/chacha-poly1305-test.c

@@ -4,13 +4,30 @@
 void
 test_main(void)
 {
-  /* From draft-agl-tls-chacha20poly1305-04 */
+  /* From draft-irtf-cfrg-chacha20-poly1305-08 */
   test_aead (&nettle_chacha_poly1305, NULL,
-	     SHEX("4290bcb154173531f314af57f3be3b50"
-		  "06da371ece272afa1b5dbdd1100a1007"),	/* key */
-	     SHEX("87e229d4500845a079c0"),		/* auth data */
-	     SHEX("86d09974840bded2a5ca"),		/* plain text */
-	     SHEX("e3e446f7ede9a19b62a4"),		/* ciphertext */
-	     SHEX("cd7cf67be39c794a"),			/* nonce */
-	     SHEX("677dabf4e3d24b876bb284753896e1d6"));	/* tag */
+	     SHEX("8081828384858687 88898a8b8c8d8e8f"
+		  "9091929394959697 98999a9b9c9d9e9f"),
+	     SHEX("50515253c0c1c2c3 c4c5c6c7"),
+	     SHEX("4c61646965732061 6e642047656e746c"
+		  "656d656e206f6620 74686520636c6173"
+		  "73206f6620273939 3a20496620492063"
+		  "6f756c64206f6666 657220796f75206f"
+		  "6e6c79206f6e6520 74697020666f7220"
+		  "7468652066757475 72652c2073756e73"
+		  "637265656e20776f 756c642062652069"
+		  "742e"),
+	     SHEX("d31a8d34648e60db7b86afbc53ef7ec2"
+		  "a4aded51296e08fea9e2b5a736ee62d6"
+		  "3dbea45e8ca9671282fafb69da92728b"
+		  "1a71de0a9e060b2905d6a5b67ecd3b36"
+		  "92ddbd7f2d778b8c9803aee328091b58"
+		  "fab324e4fad675945585808b4831d7bc"
+		  "3ff4def08e4b7a9de576d26586cec64b"
+		  "6116"),
+	     /* The draft splits the nonce into a "common part" and an
+		iv, and it seams the "common part" is the first 4
+		bytes. */
+	     SHEX("0700000040414243 44454647"),
+	     SHEX("1ae10b594f09e26a 7e902ecbd0600691"));
 }