mirror of https://github.com/oxen-io/session-ios
Added proof of work
Mikunj
6 years ago
parent
c73466f753
commit
f98a143bbe
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//
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// Copyright (c) 2018 Open Whisper Systems. All rights reserved.
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//
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import CryptoSwift
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fileprivate extension Decimal {
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/// Get the remainder of a Decimal
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static func %(lhs: Decimal, rhs: Int) -> Decimal {
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return Decimal(lhs.intValue % rhs)
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}
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/// Divide a Decimal by an Int
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static func /(lhs: Decimal, rhs: Int) -> Decimal {
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return lhs / Decimal(rhs)
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}
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/// Get the Int value of the decimal
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var intValue: Int {
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return Int(self.doubleValue)
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}
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/// Get the Double value of the decimal
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var doubleValue: Double {
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return NSDecimalNumber(decimal: self).doubleValue
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}
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/// Convert a Decimal to a UInt8 array of a given length
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func toArray(ofLength length: Int) -> [UInt8] {
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var array = [UInt8](repeating: 0, count: length)
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for i in 0..<length {
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let n = length - (i + 1)
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// 256 ** n is the value of one bit in arr[i], modulus to carry over
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// (self / 256**n) % 256;
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let denominator = pow(256, n)
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let fraction = self / denominator
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// fraction % 256
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let remainder = fraction % 256
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array[i] = UInt8(remainder.intValue)
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}
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return array
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}
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}
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// UInt8 Array specific stuff we need
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fileprivate extension Array where Element == UInt8 {
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/// Compare if lhs array is greater than rhs array
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static func >(lhs: [UInt8], rhs: [UInt8]) -> Bool {
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guard lhs.count == rhs.count else { return false }
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for i in 0..<lhs.count {
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if (lhs[i] > rhs[i]) { return true }
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if (lhs[i] < rhs[i]) { return false }
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}
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return false
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}
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/// Increment the UInt8 array by a given amount
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///
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/// - Parameter amount: The amount to increment by
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/// - Returns: The incrememnted array
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func increment(by amount: Int) -> [UInt8] {
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var newNonce = [UInt8](self)
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var increment = amount
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for i in (0..<newNonce.count).reversed() {
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guard increment > 0 else { break }
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let sum = Int(newNonce[i]) + increment
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newNonce[i] = UInt8(sum % 256)
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increment = sum / 256
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}
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return newNonce
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}
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}
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/**
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* The main logic which handles proof of work.
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*
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* This was copied from the messenger desktop.
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* Ref: libloki/proof-of-work.js
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*/
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public enum ProofOfWork {
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static let nonceLength = 8
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// Modify this value for difficulty scaling
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enum NonceTrials {
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static let development = 10
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static let production = 100
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}
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public struct Configuration {
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var pubKey: String
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var data: String
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var timestamp: Date
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var ttl: UInt
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var isDevelopment = false
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func getPayload() -> [UInt8] {
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let timestampString = String(timestamp.timeIntervalSince1970)
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let ttlString = String(ttl)
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let payloadString = timestampString + ttlString + pubKey + data
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return [UInt8](payloadString.utf8)
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}
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}
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/// Calculate a proof of work for the given configuration
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///
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/// Ref: https://bitmessage.org/wiki/Proof_of_work
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///
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/// - Parameter config: The configuration data
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/// - Returns: A nonce string or nil if it failed
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public static func calculate(with config: Configuration) -> String? {
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let payload = config.getPayload()
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let nonceTrials = config.isDevelopment ? NonceTrials.development : NonceTrials.production
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let target = calcTarget(ttl: config.ttl, payloadLength: payload.count, nonceTrials: nonceTrials)
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// Ref: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/MAX_SAFE_INTEGER
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let maxSafeInteger = pow(2, 53) - 1
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var trialValue = maxSafeInteger.toArray(ofLength: nonceLength)
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let initialHash = [UInt8](config.data.sha512().utf8)
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var nonce = [UInt8](repeating: 0, count: nonceLength)
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while trialValue > target {
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nonce = nonce.increment(by: 1)
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// This is different to the bitmessage pow
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// resultHash = hash(nonce + hash(data)) ==> hash(nonce + initialHash)
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let resultHash = (nonce + initialHash).sha512()
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trialValue = Array(resultHash[0..<8])
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}
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return nonce.toBase64()
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}
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/// Calculate the UInt8 target we need to reach
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private static func calcTarget(ttl: UInt, payloadLength: Int, nonceTrials: Int) -> [UInt8] {
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let decimalTTL = Decimal(ttl)
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let decimalPayloadLength = Decimal(payloadLength)
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let decimalNonceTrials = Decimal(nonceTrials)
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let decimalTwo16 = pow(2, 16) - 1
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let decimalTwo64 = pow(2, 64) - 1
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// ttl converted to seconds
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let ttlSeconds = decimalTTL / 1000
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// Do all the calculations
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let totalLength = decimalPayloadLength + Decimal(nonceLength)
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let ttlMult = ttlSeconds * totalLength
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let innerFrac = ttlMult / decimalTwo16
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let lenPlusInnerFrac = totalLength + innerFrac
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let denominator = decimalNonceTrials * lenPlusInnerFrac
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let targetNum = decimalTwo64 / denominator.intValue
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return targetNum.toArray(ofLength: nonceLength)
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}
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}
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