The Uniqueness of Unique Identifiers (RFC1439)
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2000-Sep-12
Internet Society Requests For Comment (RFCs)
This RFC provides information that may be useful when selecting a method to use for assigning unique identifiers to people.
Network Working Group C. Finseth
Request for Comments: 1439 University of Minnesota
The Uniqueness of Unique Identifiers
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard. Distribution of this memo is
This RFC provides information that may be useful when selecting a
method to use for assigning unique identifiers to people.
1. The Issue
Computer systems require a way to identify the people associated with
them. These identifiers have been called "user names" or "account
names." The identifers are typically short, alphanumeric strings.
In general, these identifiers must be unique.
The uniqueness is usually achieved in one of three ways:
1) The identifiers are assigned in a unique manner without using
information associated with the individual. Example identifiers are:
This method was often used by large timesharing systems. While it
achieved the uniqueness property, there was no way of guessing the
identifier without knowing it through other means.
2) The identifiers are assigned in a unique manner where the bulk of
the identifier is algorithmically derived from the individual's name.
Example identifers are:
3) The identifiers are in general not assigned in a unique manner:
the identifier is algorithmically derived from the individual's name
and duplicates are handled in an ad-hoc manner. Example identifiers
Now that we have widespread electronic mail, an important feature of
an identifier system is the ability to predict the identifier based
on other information associated with the individual. This other
information is typically the person's name.
Methods two and three make such predictions possible, especially if
you have one example mapping from a person's name to the identifier.
Method two relies on using some or all of the name and
algorithmically varying it to ensure uniqueness (for example, by
appending an integer). Method three relies on using some or all of
the name and selects an alternate identifier in the case of a
For both methods, it is important to minimize the need for making the
adjustments required to ensure uniqueness (i.e., an integer that is
not 1 or an alternate identifier). The probability that an
adjustment will be required depends on the format of the identifer
and the size of the organization.
2. Identifier Formats
There are a number of popular identifier formats. This section will
list some of them and supply both typical and maximum values for the
number of possible identifiers. A "typical" value is the number that
you are li...