1 files changed, 80 insertions, 3 deletions

diff --git a/crypto/openssl/crypto/ec/ec_key.c b/crypto/openssl/crypto/ec/ec_key.c
index 08aaac5d8a6f5..23efbd015ca47 100644
--- a/crypto/openssl/crypto/ec/ec_key.c
+++ b/crypto/openssl/crypto/ec/ec_key.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 2002-2020 The OpenSSL Project Authors. All Rights Reserved.
  * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
@@ -14,6 +14,7 @@
 #include "internal/refcount.h"
 #include <openssl/err.h>
 #include <openssl/engine.h>
+#include "crypto/bn.h"
 
 EC_KEY *EC_KEY_new(void)
 {
@@ -416,17 +417,86 @@ const BIGNUM *EC_KEY_get0_private_key(const EC_KEY *key)
 
 int EC_KEY_set_private_key(EC_KEY *key, const BIGNUM *priv_key)
 {
+    int fixed_top;
+    const BIGNUM *order = NULL;
+    BIGNUM *tmp_key = NULL;
+
     if (key->group == NULL || key->group->meth == NULL)
         return 0;
+
+    /*
+     * Not only should key->group be set, but it should also be in a valid
+     * fully initialized state.
+     *
+     * Specifically, to operate in constant time, we need that the group order
+     * is set, as we use its length as the fixed public size of any scalar used
+     * as an EC private key.
+     */
+    order = EC_GROUP_get0_order(key->group);
+    if (order == NULL || BN_is_zero(order))
+        return 0; /* This should never happen */
+
     if (key->group->meth->set_private != NULL
         && key->group->meth->set_private(key, priv_key) == 0)
         return 0;
     if (key->meth->set_private != NULL
         && key->meth->set_private(key, priv_key) == 0)
         return 0;
+
+    /*
+     * We should never leak the bit length of the secret scalar in the key,
+     * so we always set the `BN_FLG_CONSTTIME` flag on the internal `BIGNUM`
+     * holding the secret scalar.
+     *
+     * This is important also because `BN_dup()` (and `BN_copy()`) do not
+     * propagate the `BN_FLG_CONSTTIME` flag from the source `BIGNUM`, and
+     * this brings an extra risk of inadvertently losing the flag, even when
+     * the caller specifically set it.
+     *
+     * The propagation has been turned on and off a few times in the past
+     * years because in some conditions has shown unintended consequences in
+     * some code paths, so at the moment we can't fix this in the BN layer.
+     *
+     * In `EC_KEY_set_private_key()` we can work around the propagation by
+     * manually setting the flag after `BN_dup()` as we know for sure that
+     * inside the EC module the `BN_FLG_CONSTTIME` is always treated
+     * correctly and should not generate unintended consequences.
+     *
+     * Setting the BN_FLG_CONSTTIME flag alone is never enough, we also have
+     * to preallocate the BIGNUM internal buffer to a fixed public size big
+     * enough that operations performed during the processing never trigger
+     * a realloc which would leak the size of the scalar through memory
+     * accesses.
+     *
+     * Fixed Length
+     * ------------
+     *
+     * The order of the large prime subgroup of the curve is our choice for
+     * a fixed public size, as that is generally the upper bound for
+     * generating a private key in EC cryptosystems and should fit all valid
+     * secret scalars.
+     *
+     * For preallocating the BIGNUM storage we look at the number of "words"
+     * required for the internal representation of the order, and we
+     * preallocate 2 extra "words" in case any of the subsequent processing
+     * might temporarily overflow the order length.
+     */
+    tmp_key = BN_dup(priv_key);
+    if (tmp_key == NULL)
+        return 0;
+
+    BN_set_flags(tmp_key, BN_FLG_CONSTTIME);
+
+    fixed_top = bn_get_top(order) + 2;
+    if (bn_wexpand(tmp_key, fixed_top) == NULL) {
+        BN_clear_free(tmp_key);
+        return 0;
+    }
+
     BN_clear_free(key->priv_key);
-    key->priv_key = BN_dup(priv_key);
-    return (key->priv_key == NULL) ? 0 : 1;
+    key->priv_key = tmp_key;
+
+    return 1;
 }
 
 const EC_POINT *EC_KEY_get0_public_key(const EC_KEY *key)
@@ -494,6 +564,13 @@ void EC_KEY_clear_flags(EC_KEY *key, int flags)
     key->flags &= ~flags;
 }
 
+int EC_KEY_decoded_from_explicit_params(const EC_KEY *key)
+{
+    if (key == NULL || key->group == NULL)
+        return -1;
+    return key->group->decoded_from_explicit_params;
+}
+
 size_t EC_KEY_key2buf(const EC_KEY *key, point_conversion_form_t form,
                         unsigned char **pbuf, BN_CTX *ctx)
 {