Added X963KDF API

X963 KDF is used for CMS ec keyagree Recipient Info.
The X963 KDF that is used by CMS EC Key Agreement has been moved
into a EVP_KDF object. This KDF is almost identical to the the SSKDF
hash variant, so it has been implemented inside the SSKDF code with
its own method table.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/8902)

2 files changed, 43 insertions, 2 deletions

diff --git a/crypto/kdf/kdf_err.c b/crypto/kdf/kdf_err.c
index 84c330fafb..49028ab32f 100644
--- a/crypto/kdf/kdf_err.c
+++ b/crypto/kdf/kdf_err.c
@@ -65,6 +65,7 @@ static const ERR_STRING_DATA KDF_str_functs[] = {
     {ERR_PACK(ERR_LIB_KDF, KDF_F_SSKDF_NEW, 0), "sskdf_new"},
     {ERR_PACK(ERR_LIB_KDF, KDF_F_SSKDF_SIZE, 0), "sskdf_size"},
     {ERR_PACK(ERR_LIB_KDF, KDF_F_TLS1_PRF_ALG, 0), "tls1_prf_alg"},
+    {ERR_PACK(ERR_LIB_KDF, KDF_F_X963KDF_DERIVE, 0), "x963kdf_derive"},
     {0, NULL}
 };
 
@@ -84,6 +85,7 @@ static const ERR_STRING_DATA KDF_str_reasons[] = {
     {ERR_PACK(ERR_LIB_KDF, 0, KDF_R_MISSING_SESSION_ID), "missing session id"},
     {ERR_PACK(ERR_LIB_KDF, 0, KDF_R_MISSING_TYPE), "missing type"},
     {ERR_PACK(ERR_LIB_KDF, 0, KDF_R_MISSING_XCGHASH), "missing xcghash"},
+    {ERR_PACK(ERR_LIB_KDF, 0, KDF_R_NOT_SUPPORTED), "not supported"},
     {ERR_PACK(ERR_LIB_KDF, 0, KDF_R_UNKNOWN_PARAMETER_TYPE),
     "unknown parameter type"},
     {ERR_PACK(ERR_LIB_KDF, 0, KDF_R_UNSUPPORTED_MAC_TYPE),
diff --git a/crypto/kdf/sskdf.c b/crypto/kdf/sskdf.c
index 3dd5b78d26..92bf995425 100644
--- a/crypto/kdf/sskdf.c
+++ b/crypto/kdf/sskdf.c
@@ -66,10 +66,16 @@ static const unsigned char kmac_custom_str[] = { 0x4B, 0x44, 0x46 };
 /*
  * Refer to https://csrc.nist.gov/publications/detail/sp/800-56c/rev-1/final
  * Section 4. One-Step Key Derivation using H(x) = hash(x)
+ * Note: X9.63 also uses this code with the only difference being that the
+ * counter is appended to the secret 'z'.
+ * i.e.
+ *   result[i] = Hash(counter || z || info) for One Step OR
+ *   result[i] = Hash(z || counter || info) for X9.63.
  */
 static int SSKDF_hash_kdm(const EVP_MD *kdf_md,
                           const unsigned char *z, size_t z_len,
                           const unsigned char *info, size_t info_len,
+                          unsigned int append_ctr,
                           unsigned char *derived_key, size_t derived_key_len)
 {
     int ret = 0, hlen;
@@ -104,8 +110,9 @@ static int SSKDF_hash_kdm(const EVP_MD *kdf_md,
         c[3] = (unsigned char)(counter & 0xff);
 
         if (!(EVP_MD_CTX_copy_ex(ctx, ctx_init)
-                && EVP_DigestUpdate(ctx, c, sizeof(c))
+                && (append_ctr || EVP_DigestUpdate(ctx, c, sizeof(c)))
                 && EVP_DigestUpdate(ctx, z, z_len)
+                && (!append_ctr || EVP_DigestUpdate(ctx, c, sizeof(c)))
                 && EVP_DigestUpdate(ctx, info, info_len)))
             goto end;
         if (len >= out_len) {
@@ -468,7 +475,28 @@ static int sskdf_derive(EVP_KDF_IMPL *impl, unsigned char *key, size_t keylen)
             return 0;
         }
         return SSKDF_hash_kdm(impl->md, impl->secret, impl->secret_len,
-                              impl->info, impl->info_len, key, keylen);
+                              impl->info, impl->info_len, 0, key, keylen);
+    }
+}
+
+static int x963kdf_derive(EVP_KDF_IMPL *impl, unsigned char *key, size_t keylen)
+{
+    if (impl->secret == NULL) {
+        KDFerr(KDF_F_X963KDF_DERIVE, KDF_R_MISSING_SECRET);
+        return 0;
+    }
+
+    if (impl->mac != NULL) {
+        KDFerr(KDF_F_X963KDF_DERIVE, KDF_R_NOT_SUPPORTED);
+        return 0;
+    } else {
+        /* H(x) = hash */
+        if (impl->md == NULL) {
+            KDFerr(KDF_F_X963KDF_DERIVE, KDF_R_MISSING_MESSAGE_DIGEST);
+            return 0;
+        }
+        return SSKDF_hash_kdm(impl->md, impl->secret, impl->secret_len,
+                              impl->info, impl->info_len, 1, key, keylen);
     }
 }
 
@@ -482,3 +510,14 @@ const EVP_KDF ss_kdf_meth = {
     sskdf_size,
     sskdf_derive
 };
+
+const EVP_KDF x963_kdf_meth = {
+    EVP_KDF_X963,
+    sskdf_new,
+    sskdf_free,
+    sskdf_reset,
+    sskdf_ctrl,
+    sskdf_ctrl_str,
+    sskdf_size,
+    x963kdf_derive
+};