Allow specifying the tag after AAD in CCM mode

tniessen · mattcaswell · commit b48e3be947dd · 2019-05-08T11:02:42.000+01:00
This change allows to pass the authentication tag after specifying the AAD in CCM mode. This is already true for the other two supported AEAD modes (GCM and OCB) and it seems appropriate to match the behavior. GCM and OCB also support to set the tag at any point before the call to `EVP_*Final`, but this won't work for CCM due to a restriction imposed by section 2.6 of RFC3610: The tag must be set before actually decrypting data. This commit also adds a test case for setting the tag after supplying plaintext length and AAD. Reviewed-by: Paul Dale <paul.dale@oracle.com> Reviewed-by: Matt Caswell <matt@openssl.org> (Merged from #7243) (cherry picked from commit 67c81ec)
diff --git a/crypto/evp/e_aes.c b/crypto/evp/e_aes.c
@@ -3643,8 +3643,6 @@ static int aes_ccm_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
     if (!cctx->iv_set)
         return -1;
 
-    if (!EVP_CIPHER_CTX_encrypting(ctx) && !cctx->tag_set)
-        return -1;
     if (!out) {
         if (!in) {
             if (CRYPTO_ccm128_setiv(ccm, EVP_CIPHER_CTX_iv_noconst(ctx),
@@ -3659,6 +3657,11 @@ static int aes_ccm_cipher(EVP_CIPHER_CTX *ctx, unsigned char *out,
         CRYPTO_ccm128_aad(ccm, in, len);
         return len;
     }
+
+    /* The tag must be set before actually decrypting data */
+    if (!EVP_CIPHER_CTX_encrypting(ctx) && !cctx->tag_set)
+        return -1;
+
     /* If not set length yet do it */
     if (!cctx->len_set) {
         if (CRYPTO_ccm128_setiv(ccm, EVP_CIPHER_CTX_iv_noconst(ctx),
diff --git a/doc/man3/EVP_EncryptInit.pod b/doc/man3/EVP_EncryptInit.pod
@@ -412,7 +412,9 @@ The following I<ctrl>s are supported in CCM mode.
 This call is made to set the expected B<CCM> tag value when decrypting or
 the length of the tag (with the C<tag> parameter set to NULL) when encrypting.
 The tag length is often referred to as B<M>. If not set a default value is
-used (12 for AES).
+used (12 for AES). When decrypting, the tag needs to be set before passing
+in data to be decrypted, but as in GCM and OCB mode, it can be set after
+passing additional authenticated data (see L<AEAD Interface>).
 
 =item EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_L, ivlen, NULL)
 
diff --git a/test/evp_test.c b/test/evp_test.c
@@ -462,6 +462,7 @@ typedef struct cipher_data_st {
     size_t aad_len;
     unsigned char *tag;
     size_t tag_len;
+    int tag_late;
 } CIPHER_DATA;
 
 static int cipher_test_init(EVP_TEST *t, const char *alg)
@@ -525,6 +526,15 @@ static int cipher_test_parse(EVP_TEST *t, const char *keyword,
             return parse_bin(value, &cdat->aad, &cdat->aad_len);
         if (strcmp(keyword, "Tag") == 0)
             return parse_bin(value, &cdat->tag, &cdat->tag_len);
+        if (strcmp(keyword, "SetTagLate") == 0) {
+            if (strcmp(value, "TRUE") == 0)
+                cdat->tag_late = 1;
+            else if (strcmp(value, "FALSE") == 0)
+                cdat->tag_late = 0;
+            else
+                return 0;
+            return 1;
+        }
     }
 
     if (strcmp(keyword, "Operation") == 0) {
@@ -610,7 +620,7 @@ static int cipher_test_enc(EVP_TEST *t, int enc,
          * If encrypting or OCB just set tag length initially, otherwise
          * set tag length and value.
          */
-        if (enc || expected->aead == EVP_CIPH_OCB_MODE) {
+        if (enc || expected->aead == EVP_CIPH_OCB_MODE || expected->tag_late) {
             t->err = "TAG_LENGTH_SET_ERROR";
             tag = NULL;
         } else {
@@ -633,14 +643,6 @@ static int cipher_test_enc(EVP_TEST *t, int enc,
         goto err;
     }
 
-    if (!enc && expected->aead == EVP_CIPH_OCB_MODE) {
-        if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG,
-                                 expected->tag_len, expected->tag)) {
-            t->err = "TAG_SET_ERROR";
-            goto err;
-        }
-    }
-
     if (expected->aead == EVP_CIPH_CCM_MODE) {
         if (!EVP_CipherUpdate(ctx, NULL, &tmplen, NULL, out_len)) {
             t->err = "CCM_PLAINTEXT_LENGTH_SET_ERROR";
@@ -675,6 +677,15 @@ static int cipher_test_enc(EVP_TEST *t, int enc,
                 goto err;
         }
     }
+
+    if (!enc && (expected->aead == EVP_CIPH_OCB_MODE || expected->tag_late)) {
+        if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_AEAD_SET_TAG,
+                                 expected->tag_len, expected->tag)) {
+            t->err = "TAG_SET_ERROR";
+            goto err;
+        }
+    }
+
     EVP_CIPHER_CTX_set_padding(ctx, 0);
     t->err = "CIPHERUPDATE_ERROR";
     tmplen = 0;
diff --git a/test/recipes/30-test_evp_data/evpciph.txt b/test/recipes/30-test_evp_data/evpciph.txt
@@ -733,6 +733,17 @@ Ciphertext = 9a5fcccdb4cf04e7293d2775cc76a488f042382d949b43b7d6bb2b9864786726
 Operation = DECRYPT
 Result = CIPHERUPDATE_ERROR
 
+# Test that the tag can be set after specifying AAD.
+Cipher = aes-256-ccm
+Key = 1bde3251d41a8b5ea013c195ae128b218b3e0306376357077ef1c1c78548b92e
+IV = 5b8e40746f6b98e00f1d13ff41
+AAD = c17a32514eb6103f3249e076d4c871dc97e04b286699e54491dc18f6d734d4c0
+Tag = 2024931d73bca480c24a24ece6b6c2bf
+SetTagLate = TRUE
+Operation = DECRYPT
+Plaintext = 53bd72a97089e312422bf72e242377b3c6ee3e2075389b999c4ef7f28bd2b80a
+Ciphertext = 9a5fcccdb4cf04e7293d2775cc76a488f042382d949b43b7d6bb2b9864786726
+
 # AES GCM test vectors from http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf
 Cipher = aes-128-gcm
 Key = 00000000000000000000000000000000
