IceCubesApp/IceCubesNotifications/NotificationServiceSupport.swift

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import CryptoKit
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import Foundation
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extension NotificationService {
static func decrypt(payload: Data, salt: Data, auth: Data, privateKey: P256.KeyAgreement.PrivateKey, publicKey: P256.KeyAgreement.PublicKey) -> Data? {
guard let sharedSecret = try? privateKey.sharedSecretFromKeyAgreement(with: publicKey) else {
return nil
}
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let keyMaterial = sharedSecret.hkdfDerivedSymmetricKey(using: SHA256.self, salt: auth, sharedInfo: Data("Content-Encoding: auth\0".utf8), outputByteCount: 32)
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let keyInfo = info(type: "aesgcm", clientPublicKey: privateKey.publicKey.x963Representation, serverPublicKey: publicKey.x963Representation)
let key = HKDF<SHA256>.deriveKey(inputKeyMaterial: keyMaterial, salt: salt, info: keyInfo, outputByteCount: 16)
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let nonceInfo = info(type: "nonce", clientPublicKey: privateKey.publicKey.x963Representation, serverPublicKey: publicKey.x963Representation)
let nonce = HKDF<SHA256>.deriveKey(inputKeyMaterial: keyMaterial, salt: salt, info: nonceInfo, outputByteCount: 12)
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let nonceData = nonce.withUnsafeBytes(Array.init)
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guard let sealedBox = try? AES.GCM.SealedBox(combined: nonceData + payload) else {
return nil
}
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var _plaintext: Data?
do {
_plaintext = try AES.GCM.open(sealedBox, using: key)
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} catch { }
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guard let plaintext = _plaintext else {
return nil
}
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let paddingLength = Int(plaintext[0]) * 256 + Int(plaintext[1])
guard plaintext.count >= 2 + paddingLength else {
fatalError()
}
let unpadded = plaintext.suffix(from: paddingLength + 2)
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return Data(unpadded)
}
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private static func info(type: String, clientPublicKey: Data, serverPublicKey: Data) -> Data {
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var info = Data()
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info.append("Content-Encoding: ".data(using: .utf8)!)
info.append(type.data(using: .utf8)!)
info.append(0)
info.append("P-256".data(using: .utf8)!)
info.append(0)
info.append(0)
info.append(65)
info.append(clientPublicKey)
info.append(0)
info.append(65)
info.append(serverPublicKey)
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return info
}
}