Re: [edk2-devel] [PATCH v1 1/1] CryptoPkg/BaseCryptoLib: Remove unnecessary key generation.

["Li, Yi" <yi1.li@intel.com>]

Hi,

This function has a special use case: when the input PublicKey array is NULL and size is 0, the function will generate EC keypair and update context, and fill PublicKeySize with non-zero keysize to indicate success.

(CryptEc.c  L492)
  if ((PublicKey == NULL) && (*PublicKeySize != 0)) {
    return FALSE;
  }

I recommend the below changes:

  HalfSize = (EC_GROUP_get_degree (Group) + 7) / 8;

+  if ((PublicKey != NULL) && (*PublicKeySize < HalfSize * 2)) {
+    *PublicKeySize = HalfSize * 2;
+    return FALSE;
+  }
  // Assume RAND_seed was called
  if (EC_KEY_generate_key (EcKey) != 1) {
    return FALSE;
  }

-  if (*PublicKeySize < HalfSize * 2) {
+ // If PublicKey is NULL and PublicKeySize is 0, return TRUE and fill PublicKeySize with correct Key size.
+ if (*PublicKeySize == 0) {
    *PublicKeySize = HalfSize * 2;
-   return FALSE;
+   return TRUE;
  }

Regards,
Yi 

-----Original Message-----
From: levi.yun <yeoreum.yun@arm.com> 
Sent: Monday, July 17, 2023 5:54 PM
To: devel@edk2.groups.io
Cc: yeoreum.yun@arm.com; Yao, Jiewen <jiewen.yao@intel.com>; Li, Yi1 <yi1.li@intel.com>; Lu, Xiaoyu1 <xiaoyu1.lu@intel.com>; Jiang, Guomin <guomin.jiang@intel.com>; sami.mujawar@arm.com; pierre.gondois@arm.com; nd@arm.com
Subject: [PATCH v1 1/1] CryptoPkg/BaseCryptoLib: Remove unnecessary key generation.

When EcGenerateKey() is called with PublicKeySize set to zero or less than the required size, it returns the size of the required buffer with failure.
However, EcGenerateKey() generates a key and then checks if the buffer size is insufficient.
This can be optimised by moving the public key size check before generating the key.
Therefore, optimise to avoid unnecessary key generation.

Signed-off-by: levi.yun <yeoreum.yun@arm.com>
---
This changes can be seen at https://github.com/LeviYeoReum/edk2/tree/levi/2716_not_generate_key_on_fail_size_v1

 CryptoPkg/Library/BaseCryptLib/Pk/CryptEc.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/CryptoPkg/Library/BaseCryptLib/Pk/CryptEc.c b/CryptoPkg/Library/BaseCryptLib/Pk/CryptEc.c
index d8cc9ba0e8f968f6cbd9ac4c56018f9a4392cd0b..af67f512a22b23af3844b9bbc87dd57bcf952f04 100644
--- a/CryptoPkg/Library/BaseCryptLib/Pk/CryptEc.c
+++ b/CryptoPkg/Library/BaseCryptLib/Pk/CryptEc.c
@@ -497,16 +497,16 @@ EcGenerateKey (
   Group    = EC_KEY_get0_group (EcKey);
   HalfSize = (EC_GROUP_get_degree (Group) + 7) / 8;

+  if (*PublicKeySize < HalfSize * 2) {
+    *PublicKeySize = HalfSize * 2;
+    return FALSE;
+  }
+
   // Assume RAND_seed was called
   if (EC_KEY_generate_key (EcKey) != 1) {
     return FALSE;
   }

-  if (*PublicKeySize < HalfSize * 2) {
-    *PublicKeySize = HalfSize * 2;
-    return FALSE;
-  }
-
   *PublicKeySize = HalfSize * 2;

   EcPoint = EC_KEY_get0_public_key (EcKey);
--
Guid("CE165669-3EF3-493F-B85D-6190EE5B9759")
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