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42 lines
2.4 KiB
Swift
42 lines
2.4 KiB
Swift
import CryptoSwift
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import SessionProtocolKit
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import SessionUtilities
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public extension ReceivingPipeline {
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static func decryptWithSharedSenderKeys(envelope: SNProtoEnvelope, using transaction: Any) throws -> (plaintext: Data, senderPublicKey: String) {
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// 1. ) Check preconditions
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guard let groupPublicKey = envelope.source, Configuration.shared.storage.isClosedGroup(groupPublicKey) else {
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throw Error.invalidGroupPublicKey
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}
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guard let data = envelope.content else {
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throw Error.noData
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}
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guard let hexEncodedGroupPrivateKey = Configuration.shared.storage.getClosedGroupPrivateKey(for: groupPublicKey) else {
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throw Error.noGroupPrivateKey
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}
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let groupPrivateKey = Data(hex: hexEncodedGroupPrivateKey)
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let groupKeyPair = ECKeyPair(publicKey: Data(hex: groupPublicKey), privateKey: groupPrivateKey)
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// 2. ) Parse the wrapper
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let wrapper = try SNProtoClosedGroupCiphertextMessageWrapper.parseData(data)
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let ivAndCiphertext = wrapper.ciphertext
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let ephemeralPublicKey = wrapper.ephemeralPublicKey
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// 3. ) Decrypt the data inside
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guard let ephemeralSharedSecret = Curve25519.generateSharedSecret(fromPublicKey: ephemeralPublicKey, andKeyPair: groupKeyPair) else {
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throw Error.sharedSecretGenerationFailed
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}
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let salt = "LOKI"
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let symmetricKey = try HMAC(key: salt.bytes, variant: .sha256).authenticate(ephemeralSharedSecret.bytes)
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let closedGroupCiphertextMessageAsData = try AESGCM.decrypt(ivAndCiphertext, with: Data(symmetricKey))
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// 4. ) Parse the closed group ciphertext message
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let closedGroupCiphertextMessage = ClosedGroupCiphertextMessage(_throws_with: closedGroupCiphertextMessageAsData)
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let senderPublicKey = closedGroupCiphertextMessage.senderPublicKey.toHexString()
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guard senderPublicKey != Configuration.shared.storage.getUserPublicKey() else { throw Error.selfSend }
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// 5. ) Use the info inside the closed group ciphertext message to decrypt the actual message content
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let plaintext = try SharedSenderKeys.decrypt(closedGroupCiphertextMessage.ivAndCiphertext, for: groupPublicKey,
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senderPublicKey: senderPublicKey, keyIndex: UInt(closedGroupCiphertextMessage.keyIndex), using: transaction)
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// 6. ) Return
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return (plaintext, senderPublicKey)
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}
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}
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