Note: The objects described below are the desired format, the current format will soon be changed to the one mentioned below. The format below is only for the data part of the ledger transaction.
Describes the various attributes present in a credential. Contains a field called name and an ordered array of locally named references to Schema Elements (see below) and other Schemas. Every member of a schema must have a unique name. It can optionally contains a field called spec that describes the schema. Note: When a field’s "name" attribute is missing, it inherits its name from the schema or schema element that named.
{
"name": "name",
"items": [
{name: "first", element: <first_name>, encoding: <utf8_sha256>},
{name: "middle", element: <middle_name>, encoding: <utf8_sha256>},
{name: "last", element: <last_name>, encoding: <utf8_sha256>}
]
}
{
"name": "address",
"items": [
{name: "line_1", element: <address_line>, encoding: <utf8_sha256>},
{name: "line_2", element: <address_line>, encoding: <utf8_sha256>},
{name: "line_3", element: <address_line>, encoding: <utf8_sha256>},
{element: <city>, encoding: <utf8_sha256>},
{name: "state", element: <us_state>, encoding: <alpha2>},
{element: <zip_code>, encoding: <dpbc>}
]
}
{
"name": "work_address",
"spec": "address where subject is employed",
"items": [{schema: <address>, flatten: true}]
}
{
"name": "home_address",
"spec": "address where subject lives",
"items": [{schema: <address>, flatten: true}]
}
{
"name": "loan_application",
"spec": "application for a basic loan",
"items": [
{schema: <name>},
{schema: <work_address>},
{schema: <home_address>},
…
]
}
These are the low-level reusable elements that can be composed into Schema.
first_name: {spec: "subject's first given name"}
middle_name: {spec: "subject's other given names minus surname"}
surname: {spec: "subject's surname"}
address_line: {spec: "one line of a physical address"}
city: {spec: "third line of a physical address"}
us_state: {spec: "one of the states or territories of the USA"}
zip_code: {spec: "US zip code"}
birthdate: {spec: "date subject was born"}
expires: {spec: "date credential expires"}
driving_class: {spec: "US driving classification"}
hair_color: {spec: "color of the subject's hair"}
eye_color: {spec: "color of the subject's eyes"}
weight: {spec: "subject's weight"}
height: {spec: "subject's height"}
corrective_lenses: {spec: "subject is required to wear corrective lenses"}
daytime_only: {spec: "a subject's privilege is restricted to daytime"}
Data must be encoded in order to prove things about it. Cryptographic methods work with large integer in finite fields, so we must encode elements of a credential in integers.
since_1870: {spec: "date as a count of days since 1/1/1870"}
us_driving_class: {spec: "US driving class; 'standard' -> 0, 'commercial' -> 1"}
utf8_sha256: {spec: "SHA256 hash of string encoded as UTF-8"}
alpha2: {spec: "two character abbreviation"}
dpbc: {spec: "9 digit integer; 5 digit zip code encoded with trailing zeros; remove hyphen in zip+4; examples: '90210' -> 90210000, '90210-2222' -> 902102222"}
hair_color_codes: {spec: "color of hair; bald -> "BA", black -> "BL, blonde -> "BE", brown -> "BR", gray -> "GR", red/auburn -> "RA", sandy -> "SA", unknown -> "UN", white -> "WH"}
hair_color: {spec: "color of hair; 'bald' -> 9, 'black' -> 1, 'blonde' -> 2, 'brown' -> 3, 'gray' -> 4, 'red/auburn' -> 5, 'sandy' -> 6, 'unknown' -> 7, 'white' -> 8"}
eye_color: {spec: "color of eyes; 'black' -> 0, 'blue' -> 1, 'brown' -> 2, 'dichromat' -> 3, 'gray' -> 4, 'green' -> 5, 'hazel' -> 6, 'maroon' -> 7, 'pink' -> 8, 'unknown' -> 9"}
weight_lbs: {spec: "weight in whole number of pounds (avoirdupois)"}
weight_grams: {spec: "weight in whole number of grams"}
length_half_inches: {spec: "length in whole number of half inches"}
length_mm: {spec: "length in whole number of millimeters"}
bool: {spec: "'true' -> 2, 'false' -> 1, 'unknown' -> 0"}
In the case where only one encoding is used for both proving and revealing, the encoding attribute can be a simple reference to an encoding.
"encoding": "length_mm"
When different encodings are used for proving and revealing, the encoding attribute can be a value with "prove" and "reveal" attributes.
"encoding": {"prove": "utf8_sha256", "reveal": "utf8"}
When multiple encodings are included for an attribute, the encoding attribute can be an array. These encodings can be used for both proving and revealing.
"encoding": ["length_mm", "length_meters"]
If multiple encodings are used for proving, but a different encoding is used for revealing, then the encoding attribute can be an object where the "prove" attribute is an array of encodings.
"encoding": {"prove": ["utf8_sha256", "D–M Soundex"], "reveal": "utf8"}
Units of Measure
Units of measure are encapsulated in encodings. For example:
length_half_inches: {spec: "length in whole number of half inches"}
length_mm: {spec: "length in whole number of millimeters"}
Code Lists
Code lists are also encapsulated in encodings, for example:
hair_color_codes: {spec: "color of hair; bald -> 'BA', black -> 'BL', blonde -> 'BE', brown -> 'BR', gray -> 'GR', red/auburn -> 'RA', sandy -> 'SA', unknown -> 'UN', white -> 'WH'}
Fields can have a subject, which communicates who or what the attribute is about.
{
name: "person"
"items": [
{schema: <name>},
{schema: <address>},
{schema_element: <birthdate>, encoding: <since_1870>},
]
}
{
"name": "birth_certificate",
"items": [
{subject: "father", schema: <person>, flatten: true},
{subject: "mother", schema: <person>, flatten: true},
{subject: "child", schema: <person>, flatten: true},
{subject: "father", schema_element: <bloodtype>},
{subject: "mother", schema_element: <bloodtype>},
]
}