Tim Bouma wrote a post about Trusted Digital Identity.
In it he unpacks several terms including this one
Identifier: Anything (name, numbers, symbols, etc.) that uniquely distinguishes a member of a population from another member.
I don’t think this definition gets at the complexity of all the things that can be identifiers and how to distinguish them from one another. In 2014 I began working on what I called a field guide to a whole bunch of aspects of identity. This is the section that I wrote about identifiers. I am republishing it here and would love feedback – which I will incorporate into this version of the post. A complementary post is up that looks at a very nuanced discussion of what an identifier actually is What is an Identifier?.
I should say that the frame of a field guide is intentional. We are in a landscape of a range of identifier types – that we need to understand and distinguish among just like the autobahn society created the field guide to birds so we could understand them and their characteristics in different ecosystems.
For people Names are a special class of Identifiers. They are both self-asserted by people and are used to refer to them and acknowledge them in social context.
In systems, bureaucratic, digital and techno-bureaucratic identifiers are alpha numeric string pointers at/for people in systems.
This may seem simple but their are many different types and a person with a record in a system will likely have more then one type. To get these different types of identifiers I will share different examples.
Persistent Correlateable Identifiers
This type of identifier is re-used over time within contexts and across multiple contexts.
Student Number – When I enrolled at my university I was assigned an 8 digit student number. This number was persistent over my time as a student at the school. When interacting with school institutions I was asked to share this number so that activity could be linked together across different facets of the institution.
Aadhar Number – This created by Indian government for each resident of India. To get a number and individual enrolls all 10 finger prints, two iris scans and a photograph – 13 biometrics. Their is a check to see that this person has not registered already and then a number is issued to them.
Phone Number – People today often have a personal number that they use across many different contexts. It is common place to ask for a phone number to be able to contact a person. What people don’t know is that those are used to look people up in data broker services. The phone number is used to link together activity across contexts.
E-mail Address – Many people have one personal address and use it These are often used across different contexts. What people don’t know is that those are used to look people up in 9data broker services like RapLeaf.
These are assigned to individuals by systems of government and businesses to support them being re-identified when they return to an entity to interact again. This is from section 7.4.2 of the PCIM Validation Standard.
Once associated with a person, an assigned identifier uniquely distinguishes that person from all other persons in a population without the use of any other identity attributes. Examples of assigned identifiers include birth registration numbers, driver’s license numbers, and social insurance numbers. The following considerations apply to the use of assigned identifiers:
- Assigned identifiers may be kept internal to the program that maintains them. Examples of internal assigned identifiers are database unique keys and globally unique identifiers.
- Assigned identifiers maintained by one program may be provided to other programs so that those programs can also use the assigned identifier to distinguish between different persons within their program/service population; however, there may be restrictions on this practice due to privacy considerations or legislation.
- Certain assigned identifiers may be subject to legal and policy restrictions. For example, the Government of Canada imposes restrictions on the collection, use, retention, disclosure, and disposal of the social insurance number.
A directed identifier is created to support individuals using different identifiers in different contexts. The purpose of this is to inhibit the ability to link records across contexts.
The British Columbia eID System – This system enrolls citizens and issues a card to them. When the card is used to access different government systems by the citizens. It does not use one identifier for the citizen. Rather for each system it uses a different identifier for the system – an identifier directed for a particular system.
Decentralized Identifiers, DIDs – this type of identifier can be easily created and therefore can be directed – meaning that individuals only use a particular DID for interacting with a particular institution. The reverse is also true. Institutions can created a separate DID for each connection they have to each individual. Sovrin and Veres One are working on creating ways for directed identifiers being accessible to individuals and institutions to manage their connections to one another.
By combining a name names, and key attributes together systems use this combination to create a defacto identifier which uniquely identifies a person often in the context of a whole society. An example is the us of “name” “birth date” and “birth place”. It seems innocent enough to be asked for one’s name, birthdate and place but this becomes a persistent correlateable identifier to link and track activity across many systems. The creation of defacto identifiers that are persistent and correlateable limits people’s ability to control how they present in different contexts.
In the process of creating a feedback loop related to this article Tim pointed to section 7 of this work under development by thePan Canadian Identity Management efforts. Now his definition above makes more sense. In section 7.4 they talk about identity this way. They are oriented to defect identifiers to ensure uniqueness.
A property or characteristic associated with an identifiable person is referred to as an identity attribute or an identity data element. Examples of identity attributes include name, date of birth, and sex. For any given program or service, identity information is the set of identity attributes that is both:
- Sufficient to distinguish between different persons within the program/service population (i.e. achieve the uniqueness requirement for identity); and
- Sufficient to describe the person as required by the program or service.
Section 7.4.1 says this:
The set of identity attributes that is used to uniquely distinguish a unique and particular person within a program/service population is referred to as an identifier
An opaque identifier is one that does not give away information about the subject it identifies.
Examples of Opaque Identifiers
The BC Government eID program has at its core an opaque identifier on each card – it points to their card record. It is just a number with no meaning. If they loose their card a new opaque identifier is issued for their next card.
Examples of Non-Opaque Identifiers
Examples of Non-Opaque Identifiers
- YYMMDD represents the date of birth (DoB);
- SSSS is a sequence number registered with the same birth date (where females are assigned sequential numbers in the range 0000 to 4999 and males from 5000 to 9999);
- C is the citizenship with 0 if the person is a SA citizen, 1 if the person is a permanent resident;
- A is 8 or 9. Prior to 1994 this number was used to indicate the holder’s race;
The US Social Security Number is created via a formula and so the number gives away information about the person it identifiers.
Phone numbers give away information about the metro region that a person was issued the number from.
Some identifiers that represent people are also end-points to which messages can be sent.
It is often forgotten in conversations about digital identity that we had a system of end-points for people before networks known as a mailing address. They system of mailing addresses was developed and is maintained by the US postal service.
Phone Number – Now with cellular phones people have their own phone numbers (not just one for a household or their workplace as a whole). This permits both voice calls being made, text messages and MMS Multi-Media messages. The name space for phone number originates from the ITU-T. They are globally unique. They are also recyclable.
E-mail Address – These addresses permit people to send messages to the address they have. They are globally unique. The name space for domain names resides with ICANN. They are also recyclable.
Many digital devices have unique identifiers. Activity on digital networks can be linked together by tracking these activity originating from particular devices even if people using them .
These are identifiers that do not resolve in digital or physical networks.
Documents like birth certificates have serial numbers that identify the document.
Document Validation Systems
These systems are used to look up which documents are infact valid. When properly constructed they don’t give away any information about the person. Those using the system type in the serial number of the document and information it contains and the system simply returns a Yes/No answer about weather it is valid or not.
A beacon actually broadcasts from a digital device a persistent correlateable identifier to any device that asks for it. It creates a form of tracking people and their devices in the physical world.
RFID chips, cellular phones, laptop computers
These systems generate different identifiers depending on context.
The BC eID system way of using one card that then supports the use of different identifiers depending on context.
Time Limited & Revocable
Some identifiers are created and point at a person but are revocable. An example is a phone number that is after one stops paying one’s phone bill for a month is re-assigned to another person. An employee at a company may have an employee number that is revoked (no longer valid) once employment is terminated. A passport number is an identifier that has a time limit it is good for 5 or 10 years. A landed immigrant card (green card) in the US is only good for 10 years.
These identifiers are persistent and are not revoked. Examples include Social Security Numbers.
Some identifiers are in systems where identifiers that point at one person can be discontinued (they stop paying their phone bill or using their e-mail address) and then the identifier can be re-assigned to a different user.
Delegation (Acting on Behalf of Another)
This functionality is critically to a variety of user populations. Elders who want to delegate access to their accounts children. Service professionals who have contractual relationships with clients such as an accountant managing access to financial & tax records. Most systems are designed with an assumption that people themselves are the only one accessing accounts. This creates a problem when people want to delegate access they have to turn over their own credentials so the person they are delegating to “pretends” to be the actual user.
Stewardship (Care-Taking – Oversight)
Their is another role that is slightly different then delegation when someone turns over a power of attorney like function for a particular account/set of functions. Stewardship of identity is the type of relationship a parent has for a child’s identity or the type of care needed to help the mentally disabled with their interactions online.
The Mesh of Pointers
We end-up with a way that identifiers work together as a web of pointers towards a particular individual.