Add EVP_aead_chacha20_poly1305_ietf() - The informational RFC 7539,

"ChaCha20 and Poly1305 for IETF Protocols", introduced a modified AEAD
construction that is incompatible with the common style that has been
already used in TLS with EVP_aead_chacha20_poly1305().  The IETF
version also adds a constant (salt) that is prepended to the nonce.

OK mikeb@ jsing@

1 files changed, 111 insertions, 18 deletions

diff --git a/src/lib/libcrypto/evp/e_chacha20poly1305.c b/src/lib/libcrypto/evp/e_chacha20poly1305.c
index 9deb40b72a..47551c4578 100644
--- a/src/lib/libcrypto/evp/e_chacha20poly1305.c
+++ b/src/lib/libcrypto/evp/e_chacha20poly1305.c
@@ -1,5 +1,7 @@
-/* $OpenBSD: e_chacha20poly1305.c,v 1.10 2015/09/10 15:56:25 jsing Exp $ */
+/* $OpenBSD: e_chacha20poly1305.c,v 1.11 2015/11/02 15:40:53 reyk Exp $ */
+
 /*
+ * Copyright (c) 2015 Reyk Floter <reyk@openbsd.org>
  * Copyright (c) 2014, Google Inc.
  *
  * Permission to use, copy, modify, and/or distribute this software for any
@@ -32,6 +34,16 @@
 #define POLY1305_TAG_LEN 16
 #define CHACHA20_NONCE_LEN 8
 
+/*
+ * The informational RFC 7539, "ChaCha20 and Poly1305 for IETF Protocols",
+ * introduced a modified AEAD construction that is incompatible with the
+ * common style that that has been already used in TLS.  The IETF version
+ * also adds a constant (salt) that is prepended to the nonce.
+ */
+#define CHACHA20_CONSTANT_LEN 4
+#define CHACHA20_IV_LEN 8
+#define CHACHA20_NONCE_LEN_IETF (CHACHA20_CONSTANT_LEN + CHACHA20_IV_LEN)
+
 struct aead_chacha20_poly1305_ctx {
         unsigned char key[32];
         unsigned char tag_len;
@@ -88,10 +100,27 @@ poly1305_update_with_length(poly1305_state *poly1305,
                 j >>= 8;
         }
 
-        CRYPTO_poly1305_update(poly1305, data, data_len);
+        if (data != NULL)
+                CRYPTO_poly1305_update(poly1305, data, data_len);
         CRYPTO_poly1305_update(poly1305, length_bytes, sizeof(length_bytes));
 }
 
+static void
+poly1305_update_with_pad16(poly1305_state *poly1305,
+    const unsigned char *data, size_t data_len)
+{
+        static const unsigned char zero_pad16[16];
+        size_t pad_len;
+
+        CRYPTO_poly1305_update(poly1305, data, data_len);
+
+        /* pad16() is defined in RFC 7539 2.8.1. */
+        if ((pad_len = data_len % 16) == 0)
+                return;
+
+        CRYPTO_poly1305_update(poly1305, zero_pad16, 16 - pad_len);
+}
+
 static int
 aead_chacha20_poly1305_seal(const EVP_AEAD_CTX *ctx, unsigned char *out,
     size_t *out_len, size_t max_out_len, const unsigned char *nonce,
@@ -101,7 +130,9 @@ aead_chacha20_poly1305_seal(const EVP_AEAD_CTX *ctx, unsigned char *out,
         const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
         unsigned char poly1305_key[32];
         poly1305_state poly1305;
+        const unsigned char *iv;
         const uint64_t in_len_64 = in_len;
+        uint64_t ctr;
 
         /* The underlying ChaCha implementation may not overflow the block
          * counter into the second counter word. Therefore we disallow
@@ -121,19 +152,40 @@ aead_chacha20_poly1305_seal(const EVP_AEAD_CTX *ctx, unsigned char *out,
                 return 0;
         }
 
-        if (nonce_len != CHACHA20_NONCE_LEN) {
+        if (nonce_len != ctx->aead->nonce_len) {
                 EVPerr(EVP_F_AEAD_CHACHA20_POLY1305_SEAL, EVP_R_IV_TOO_LARGE);
                 return 0;
         }
 
-        memset(poly1305_key, 0, sizeof(poly1305_key));
-        CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
-            c20_ctx->key, nonce, 0);
-
-        CRYPTO_poly1305_init(&poly1305, poly1305_key);
-        poly1305_update_with_length(&poly1305, ad, ad_len);
-        CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
-        poly1305_update_with_length(&poly1305, out, in_len);
+        if (nonce_len == CHACHA20_NONCE_LEN) {
+                /* Google's draft-agl-tls-chacha20poly1305-04, Nov 2013 */
+
+                memset(poly1305_key, 0, sizeof(poly1305_key));
+                CRYPTO_chacha_20(poly1305_key, poly1305_key,
+                    sizeof(poly1305_key), c20_ctx->key, nonce, 0);
+
+                CRYPTO_poly1305_init(&poly1305, poly1305_key);
+                poly1305_update_with_length(&poly1305, ad, ad_len);
+                CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, nonce, 1);
+                poly1305_update_with_length(&poly1305, out, in_len);
+        } else if (nonce_len == CHACHA20_NONCE_LEN_IETF) {
+                /* RFC 7539, May 2015 */
+
+                ctr = (uint64_t)(nonce[0] | nonce[1] << 8 |
+                    nonce[2] << 16 | nonce[3] << 24) << 32;
+                iv = nonce + CHACHA20_CONSTANT_LEN;
+
+                memset(poly1305_key, 0, sizeof(poly1305_key));
+                CRYPTO_chacha_20(poly1305_key, poly1305_key,
+                    sizeof(poly1305_key), c20_ctx->key, iv, ctr);
+
+                CRYPTO_poly1305_init(&poly1305, poly1305_key);
+                poly1305_update_with_pad16(&poly1305, ad, ad_len);
+                CRYPTO_chacha_20(out, in, in_len, c20_ctx->key, iv, ctr + 1);
+                poly1305_update_with_pad16(&poly1305, out, in_len);
+                poly1305_update_with_length(&poly1305, NULL, ad_len);
+                poly1305_update_with_length(&poly1305, NULL, in_len);
+        }
 
         if (c20_ctx->tag_len != POLY1305_TAG_LEN) {
                 unsigned char tag[POLY1305_TAG_LEN];
@@ -157,9 +209,11 @@ aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, unsigned char *out,
         const struct aead_chacha20_poly1305_ctx *c20_ctx = ctx->aead_state;
         unsigned char mac[POLY1305_TAG_LEN];
         unsigned char poly1305_key[32];
+        const unsigned char *iv;
         poly1305_state poly1305;
         const uint64_t in_len_64 = in_len;
         size_t plaintext_len;
+        uint64_t ctr;
 
         if (in_len < c20_ctx->tag_len) {
                 EVPerr(EVP_F_AEAD_CHACHA20_POLY1305_OPEN, EVP_R_BAD_DECRYPT);
@@ -178,7 +232,7 @@ aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, unsigned char *out,
                 return 0;
         }
 
-        if (nonce_len != CHACHA20_NONCE_LEN) {
+        if (nonce_len != ctx->aead->nonce_len) {
                 EVPerr(EVP_F_AEAD_CHACHA20_POLY1305_OPEN, EVP_R_IV_TOO_LARGE);
                 return 0;
         }
@@ -191,13 +245,34 @@ aead_chacha20_poly1305_open(const EVP_AEAD_CTX *ctx, unsigned char *out,
                 return 0;
         }
 
-        memset(poly1305_key, 0, sizeof(poly1305_key));
-        CRYPTO_chacha_20(poly1305_key, poly1305_key, sizeof(poly1305_key),
-            c20_ctx->key, nonce, 0);
+        if (nonce_len == CHACHA20_NONCE_LEN) {
+                /* Google's draft-agl-tls-chacha20poly1305-04, Nov 2013 */
+
+                memset(poly1305_key, 0, sizeof(poly1305_key));
+                CRYPTO_chacha_20(poly1305_key, poly1305_key,
+                    sizeof(poly1305_key), c20_ctx->key, nonce, 0);
+
+                CRYPTO_poly1305_init(&poly1305, poly1305_key);
+                poly1305_update_with_length(&poly1305, ad, ad_len);
+                poly1305_update_with_length(&poly1305, in, plaintext_len);
+        } else if (nonce_len == CHACHA20_NONCE_LEN_IETF) {
+                /* RFC 7539, May 2015 */
+
+                ctr = (uint64_t)(nonce[0] | nonce[1] << 8 |
+                    nonce[2] << 16 | nonce[3] << 24) << 32;
+                iv = nonce + CHACHA20_CONSTANT_LEN;
+
+                memset(poly1305_key, 0, sizeof(poly1305_key));
+                CRYPTO_chacha_20(poly1305_key, poly1305_key,
+                    sizeof(poly1305_key), c20_ctx->key, iv, ctr);
+
+                CRYPTO_poly1305_init(&poly1305, poly1305_key);
+                poly1305_update_with_pad16(&poly1305, ad, ad_len);
+                poly1305_update_with_pad16(&poly1305, in, plaintext_len);
+                poly1305_update_with_length(&poly1305, NULL, ad_len);
+                poly1305_update_with_length(&poly1305, NULL, plaintext_len);
+        }
 
-        CRYPTO_poly1305_init(&poly1305, poly1305_key);
-        poly1305_update_with_length(&poly1305, ad, ad_len);
-        poly1305_update_with_length(&poly1305, in, plaintext_len);
         CRYPTO_poly1305_finish(&poly1305, mac);
 
         if (timingsafe_memcmp(mac, in + plaintext_len, c20_ctx->tag_len) != 0) {
@@ -222,10 +297,28 @@ static const EVP_AEAD aead_chacha20_poly1305 = {
         .open = aead_chacha20_poly1305_open,
 };
 
+static const EVP_AEAD aead_chacha20_poly1305_ietf = {
+        .key_len = 32,
+        .nonce_len = CHACHA20_NONCE_LEN_IETF,
+        .overhead = POLY1305_TAG_LEN,
+        .max_tag_len = POLY1305_TAG_LEN,
+
+        .init = aead_chacha20_poly1305_init,
+        .cleanup = aead_chacha20_poly1305_cleanup,
+        .seal = aead_chacha20_poly1305_seal,
+        .open = aead_chacha20_poly1305_open,
+};
+
 const EVP_AEAD *
 EVP_aead_chacha20_poly1305()
 {
         return &aead_chacha20_poly1305;
 }
 
+const EVP_AEAD *
+EVP_aead_chacha20_poly1305_ietf()
+{
+        return &aead_chacha20_poly1305_ietf;
+}
+
 #endif  /* !OPENSSL_NO_CHACHA && !OPENSSL_NO_POLY1305 */