five-bells-condition
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Implementation of crypto-conditions in JavaScript
355 lines (313 loc) • 11.4 kB
JavaScript
/**
* @module types
*/
const Condition = require('../lib/condition')
const Fulfillment = require('../lib/fulfillment')
const BaseSha256 = require('./base-sha256')
const MissingDataError = require('../errors/missing-data-error')
const isInteger = require('../util/is-integer')
const Asn1ThresholdFingerprintContents = require('../schemas/fingerprint').ThresholdFingerprintContents
const CONDITION = 'condition'
const FULFILLMENT = 'fulfillment'
/**
* THRESHOLD-SHA-256: Threshold gate condition using SHA-256.
*
* Threshold conditions can be used to create m-of-n multi-signature groups.
*
* Threshold conditions can represent the AND operator by setting the threshold
* to equal the number of subconditions (n-of-n) or the OR operator by setting
* the thresold to one (1-of-n).
*
* Since threshold conditions operate on conditions, they can be nested as well
* which allows the creation of deep threshold trees of public keys.
*
* By using Merkle trees, threshold fulfillments do not need to to provide the
* structure of unfulfilled subtrees. That means only the public keys that are
* actually used in a fulfillment, will actually appear in the fulfillment,
* saving space.
*
* One way to formally interpret a threshold condition is as a booleanthreshold
* gate. A tree of threshold conditions forms a boolean threshold circuit.
*
* THRESHOLD-SHA-256 is assigned the type ID 2. It relies on the SHA-256 and
* THRESHOLD feature suites which corresponds to a feature bitmask of 0x09.
*/
class ThresholdSha256 extends BaseSha256 {
constructor () {
super()
this.threshold = null
this.subconditions = []
}
/**
* Add a subcondition (unfulfilled).
*
* This can be used to generate a new threshold condition from a set of
* subconditions or to provide a non-fulfilled subcondition when creating a
* threshold fulfillment.
*
* @param {Condition|String} subcondition Condition object or URI string
* representing a new subcondition to be added.
*/
addSubcondition (subcondition) {
if (typeof subcondition === 'string') {
subcondition = Condition.fromUri(subcondition)
} else if (!(subcondition instanceof Condition)) {
throw new Error('Subconditions must be URIs or objects of type Condition')
}
this.subconditions.push({
type: CONDITION,
body: subcondition
})
}
/**
* Add a fulfilled subcondition.
*
* When constructing a threshold fulfillment, this method allows you to
* provide a fulfillment for one of the subconditions.
*
* Note that you do **not** have to add the subcondition if you're adding the
* fulfillment. The condition can be calculated from the fulfillment and will
* be added automatically.
*
* @param {Fulfillment|String} subfulfillment Fulfillment object or URI string
* representing a new subfulfillment to be added.
*/
addSubfulfillment (subfulfillment) {
if (typeof subfulfillment === 'string') {
subfulfillment = Fulfillment.fromUri(subfulfillment)
} else if (!(subfulfillment instanceof Fulfillment)) {
throw new Error('Subfulfillments must be URIs or objects of type Fulfillment')
}
this.subconditions.push({
type: FULFILLMENT,
body: subfulfillment
})
}
/**
* Set the threshold.
*
* Determines the threshold that is used to consider this condition fulfilled.
* If the number of valid subfulfillments is greater or equal to this number,
* the threshold condition is considered to be fulfilled.
*
* @param {Number} threshold Integer threshold
*/
setThreshold (threshold) {
if (!isInteger(threshold) || threshold < 1) {
throw new TypeError('Threshold must be a integer greater than zero, was: ' +
threshold)
}
this.threshold = threshold
}
/**
* Get set of used type names.
*
* This is a type of condition that can contain subconditions. A complete
* set of subtypes must contain all types that must be supported in order to
* validate this fulfillment. Therefore, we need to join the type of this
* fulfillment with all of the sets of subtypes for each of the subconditions.
*
* @return {Number} Complete set of types for this fulfillment.
*/
getSubtypes () {
const typeSets = this.subconditions
.map(x => Array.from(x.body.getSubtypes()).concat(x.body.getTypeName()))
const subtypes = new Set(Array.prototype.concat.apply([], typeSets))
// Never include our own type as a subtype. The reason is that we already
// know that the validating implementation knows how to interpret this type,
// otherwise it wouldn't be able to verify this fulfillment to begin with.
subtypes.delete(this.constructor.TYPE_NAME)
return subtypes
}
/**
* Comparison function used to pre-sort conditions due to lack of sorting
* support in our current DER encoder of choice.
*
* See: https://github.com/indutny/asn1.js/issues/80
*
* @param {Condition} a First condition to compare
* @param {Condition} b Second condition to compare
*
* @private
*/
static compareConditions (a, b) {
return Buffer.compare(a.serializeBinary(), b.serializeBinary())
}
/**
* Produce the contents of the condition hash.
*
* This function is called internally by the `getCondition` method.
*
* @return {Buffer} Encoded contents of fingerprint hash.
*
* @private
*/
getFingerprintContents () {
return Asn1ThresholdFingerprintContents.encode({
threshold: this.threshold,
subconditions: this.subconditions
.map(x => (
x.body instanceof Condition
? x.body
: x.body.getCondition()
))
.sort(ThresholdSha256.compareConditions)
.map(x => x.getAsn1Json())
})
}
/**
* Calculate the cost of fulfilling this condition.
*
* In a threshold condition, the cost consists of the t most expensive
* subconditions plus n times 32 where t is the threshold and n is the
* total number of subconditions.
*
* @return {Number} Expected maximum cost to fulfill this condition
* @private
*/
calculateCost () {
// Calculate length of longest fulfillments
const subconditions = this.subconditions
.map(this.constructor.getSubconditionCost)
const worstCaseFulfillmentsCost =
this.constructor.calculateWorstCaseLength(
this.threshold,
subconditions
)
if (worstCaseFulfillmentsCost === -Infinity) {
throw new MissingDataError('Insufficient number of subconditions to meet the threshold')
}
return worstCaseFulfillmentsCost + 1024 * subconditions.length
}
static getSubconditionCost (cond) {
return cond.type === FULFILLMENT
? cond.body.getCondition().getCost()
: cond.body.getCost()
}
/**
* Calculate the worst case cost of a set of subconditions.
*
* Given a set of costs C and a threshold t, it returns the sum of the largest
* t elements in C.
*
* @param {Number} threshold Threshold that the remaining subconditions have
* to meet.
* @param {Number[]} subconditionCosts Set of subconditions.
* @return {Number} Maximum cost of a valid, minimal set of fulfillments or
* -Infinity if there is no valid set.
*
* @private
*/
static calculateWorstCaseLength (threshold, subconditionCosts) {
if (subconditionCosts.length < threshold) {
return -Infinity
}
return subconditionCosts
.sort((a, b) => a - b)
.slice(-threshold)
.reduce((total, size) => total + size, 0)
}
parseJson (json) {
this.setThreshold(json.threshold)
if (json.subfulfillments) {
for (let fulfillmentJson of json.subfulfillments) {
this.addSubfulfillment(Fulfillment.fromJson(fulfillmentJson))
}
}
if (json.subconditions) {
for (let conditionJson of json.subconditions) {
this.addSubcondition(Condition.fromJson(conditionJson))
}
}
}
parseAsn1JsonPayload (json) {
this.setThreshold(json.subfulfillments.length)
if (json.subfulfillments) {
for (let fulfillmentJson of json.subfulfillments) {
this.addSubfulfillment(Fulfillment.fromAsn1Json(fulfillmentJson))
}
}
if (json.subconditions) {
for (let conditionJson of json.subconditions) {
this.addSubcondition(Condition.fromAsn1Json(conditionJson))
}
}
}
getAsn1JsonPayload () {
const fulfillments = this.subconditions.filter(x => x.type === FULFILLMENT)
.sort((a, b) => a.body.getCondition().getCost() - b.body.getCondition().getCost())
const conditions = this.subconditions.filter(x => x.type === CONDITION)
if (fulfillments.length < this.threshold) {
throw new Error('Not enough fulfillments')
}
const minimalFulfillments = fulfillments
.slice(0, this.threshold)
const remainingConditions = conditions
.map(x => x.body)
.concat(
fulfillments
.slice(this.threshold)
.map(x => x.body.getCondition())
)
return {
subfulfillments: minimalFulfillments
.map(x => x.body)
.sort(ThresholdSha256.compareConditions)
.map(x => x.getAsn1Json()),
subconditions: remainingConditions
.sort(ThresholdSha256.compareConditions)
.map(x => x.getAsn1Json())
}
}
/**
* Select the smallest valid set of fulfillments.
*
* From a set of fulfillments, selects the smallest combination of
* fulfillments which meets the given threshold.
*
* @param {Number} threshold (Remaining) threshold that must be met.
* @param {Object[]} fulfillments Set of fulfillments
* @return {Object[]} Minimal set of fulfillments.
*
* @private
*/
static calculateSmallestValidFulfillmentSet (threshold, fulfillments) {
fulfillments.sort((a, b) => b.size - a.size)
return fulfillments.slice(0, threshold)
}
/**
* Check whether this fulfillment meets all validation criteria.
*
* This will validate the subfulfillments and verify that there are enough
* subfulfillments to meet the threshold.
*
* @param {Buffer} message Message to validate against.
* @return {Boolean} Whether this fulfillment is valid.
*/
validate (message) {
const fulfillments = this.subconditions.filter((cond) => cond.type === FULFILLMENT)
// Number of fulfilled conditions must meet the threshold
if (fulfillments.length < this.threshold) {
throw new Error('Threshold not met')
}
// But the set must be minimal, there mustn't be any fulfillments
// we could take out
if (fulfillments.length > this.threshold) {
throw new Error('Fulfillment is not minimal')
}
// Ensure all subfulfillments are valid
return fulfillments.every((f) => f.body.validate(message))
}
}
ThresholdSha256.TYPE_ID = 2
ThresholdSha256.TYPE_NAME = 'threshold-sha-256'
ThresholdSha256.TYPE_ASN1_CONDITION = 'thresholdSha256Condition'
ThresholdSha256.TYPE_ASN1_FULFILLMENT = 'thresholdSha256Fulfillment'
ThresholdSha256.TYPE_CATEGORY = 'compound'
// DEPRECATED
ThresholdSha256.prototype.addSubconditionUri =
ThresholdSha256.prototype.addSubcondition
ThresholdSha256.prototype.addSubfulfillmentUri =
ThresholdSha256.prototype.addSubfulfillment
module.exports = ThresholdSha256