patch proposition for #425

@@ -2696,10 +2696,11 @@ sc_pkcs15_get_object_guid(struct sc_pkcs15_card *p15card, const struct sc_pkcs15
 	struct sc_context *ctx = p15card->card->ctx;
 	struct sc_serial_number serialnr;
 	struct sc_pkcs15_id  id;
 	unsigned char guid_bin[SC_PKCS15_MAX_ID_SIZE + SC_MAX_SERIALNR];
 	int rv;
+	int inputSize;
 
 	LOG_FUNC_CALLED(ctx);
 	if(!out || !out_size)
 		LOG_FUNC_RETURN(ctx, SC_ERROR_INVALID_ARGUMENTS);
 
@@ -2746,20 +2747,27 @@ sc_pkcs15_get_object_guid(struct sc_pkcs15_card *p15card, const struct sc_pkcs15
 	}
 
 	memset(guid_bin, 0, sizeof(guid_bin));
 	memcpy(guid_bin, id.value, id.len);
 	memcpy(guid_bin + id.len, serialnr.value, serialnr.len);
-
-	// If OpenSSL is available (SHA1), then rather use the hash of the data
-	// - this also protects against data being too short
+	inputSize = id.len + serialnr.len;
+        // If OpenSSL is available (SHA1), then rather use the hash of the data
+        // - this also protects against data being too short
 #ifdef ENABLE_OPENSSL
-	SHA1(guid_bin, id.len + serialnr.len, guid_bin);
-	id.len = SHA_DIGEST_LENGTH;
-	serialnr.len = 0;
+	SHA1(guid_bin, inputSize, guid_bin);
+	inputSize = SHA_DIGEST_LENGTH;
+#else
+	if (inputSize < 16)
+	{
+		/* guid_bin has a size larger than 16 bytes
+		force the remaining bytes up to 16 bytes to be zero
+		so sc_pkcs15_serialize_guid won't fail because the size is less than 16*/
+		inputSize = 16;
+	}
 #endif
 
-	rv = sc_pkcs15_serialize_guid(guid_bin, id.len + serialnr.len, flags, (char *)out, *out_size);
+	rv = sc_pkcs15_serialize_guid(guid_bin, inputSize, flags, (char *)out, *out_size);
 	LOG_TEST_RET(ctx, rv, "Serialize GUID error");
 
 	*out_size = strlen((char *)out);
 	LOG_FUNC_RETURN(ctx, rv);
 }

define SC_PKCS15_MAX_ID_SIZE 255

define SC_MAX_SERIALNR 32

Without some combination of id and serial number, the resulting GUID could contain only the ID if the ID is long. if id_len/2 > out_size (if I did the math correctly.)
out_size is 40 bytes.
I believe his could result in guids that are the same for multiple cards.