37 lines
1.5 KiB
Swift
37 lines
1.5 KiB
Swift
import SessionSnodeKit
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import SessionUtilitiesKit
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enum ProofOfWork {
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/// A modified version of [Bitmessage's Proof of Work Implementation](https://bitmessage.org/wiki/Proof_of_work).
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static func calculate(ttl: UInt64, publicKey: String, data: String) -> (timestamp: UInt64, base64EncodedNonce: String)? {
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let nonceSize = MemoryLayout<UInt64>.size
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// Get millisecond timestamp
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let timestamp = NSDate.millisecondTimestamp()
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// Construct payload
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let payloadAsString = String(timestamp) + String(ttl) + publicKey + data
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let payload = payloadAsString.bytes
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// Calculate target
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let numerator = UInt64.max
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let difficulty = UInt64(1)
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let totalSize = UInt64(payload.count + nonceSize)
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let ttlInSeconds = ttl / 1000
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let denominator = difficulty * (totalSize + (ttlInSeconds * totalSize) / UInt64(UInt16.max))
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let target = numerator / denominator
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// Calculate proof of work
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var value = UInt64.max
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let payloadHash = payload.sha512()
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var nonce = UInt64(0)
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while value > target {
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nonce = nonce &+ 1
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let hash = (nonce.bigEndianBytes + payloadHash).sha512()
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guard let newValue = UInt64(fromBigEndianBytes: [UInt8](hash[0..<nonceSize])) else { return nil }
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value = newValue
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}
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// Encode as base 64
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let base64EncodedNonce = nonce.bigEndianBytes.toBase64()!
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// Return
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return (timestamp, base64EncodedNonce)
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}
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}
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