Globally Unique Identifier

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A Globally Unique Identifier ( GUID [ gu: id ]) is a number with 128 bits (16 bytes ) that is used in distributed computer systems. GUID is an implementation of the Universally Unique Identifier Standard (UUID).

GUIDs are usually represented in the 8-4-4-4-12 format XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX , where each X stands for a character from the hexadecimal system and can therefore be a digit 0–9 or a letter A – F , e.g. B. 936DA01F-9ABD-4D9D-80C7-02AF85C822A8 (32 letters / digits, 36 characters with hyphens).

The four most significant bits of the third block (counting from the left) indicate the version of the GUID, from which one can infer the type of algorithm used to generate the GUID. The up to three most significant bits of the fourth block identify the variant used. In the example, the version can be identified by the 4 and the variant by the 8 in 936DA01F-9ABD- 4 D9D- 8 0C7-02AF85C822A8. The same variant as in the example could also be identified by a 9, an A or B instead of an 8, since only the first two bits count for this variant ( 10xx).

GUID approach

A conceivable possibility of obtaining a unique identifier would be allocation by a central registry. For computer network cards there is already such a central registry for the underlying MAC addresses . Assuming that a computer can only create one new data record at a time, a globally unique identifier for the data record can be determined from the MAC address of the creating computer and the time stamp. Version 1 GUIDs are based on the MAC address and the current time of the calculating system. The use of the MAC address is controversial because it shows whether a particular host is the originator of a GUID. This can compromise the privacy of the GUID creators.

In the current version 4, the MAC address is no longer used to generate GUIDs. It is therefore hardly possible to draw conclusions about the author. The majority of a GUID is now a pseudo-random number, which is not, however, cryptographically secure .

application

In Microsoft's Windows operating systems , GUIDs are used in many places, for example to uniquely identify Office documents, COM interfaces or Active-X controls.

Another application is the identification of volumes and partition types in the GUID Partition Table .

A GUID can be saved as a replication ID.

Web links

Individual evidence

  1. ↑ Leach, Paul J., Mealling, Michael, Salz, Rich: A Universally Unique IDentifier (UUID) URN Namespace. Internet Engineering Task Force, July 2015, accessed March 22, 2018 .
  2. ^ Peter Siering, Christian Persson : Big Brother Bill. Microsoft's secret ID numbers - supposedly a glitch . In: c't . heise Verlag, Hanover June 1999 ( online ).