pkcs15-sec: Remove logging after PKCS#1 v1.5 depadding

To prevent Marvin attack on RSA PKCS#1 v1.5 padding
when logging the return value, signaling the padding error.

src/libopensc/pkcs15-sec.c

@@ -308,10 +308,10 @@ int sc_pkcs15_decipher(struct sc_pkcs15_card *p15card,
 
  /* Strip any padding */
  if (pad_flags & SC_ALGORITHM_RSA_PAD_PKCS1) {
- int s = r;
- int key_size = alg_info->key_length;
+ unsigned int s = r;
+ unsigned int key_size = (unsigned int)alg_info->key_length;
  r = sc_pkcs1_strip_02_padding_constant_time(ctx, key_size / 8, out, s, out, &s);
- LOG_TEST_RET(ctx, r, "Invalid PKCS#1 padding");
+ /* for keeping PKCS#1 v1.5 depadding constant-time, do not log error here */
  }
 #ifdef ENABLE_OPENSSL
  if (pad_flags & SC_ALGORITHM_RSA_PAD_OAEP)
@@ -333,7 +333,8 @@ int sc_pkcs15_decipher(struct sc_pkcs15_card *p15card,
  LOG_TEST_RET(ctx, r, "Invalid OAEP padding");
  }
 #endif
- LOG_FUNC_RETURN(ctx, r);
+ /* do not log error code to prevent side channel attack */
+ return r;
 }
 
 /* derive one key from another. RSA can use decipher, so this is for only ECDH