session-ios/SessionMessagingKit/Sending & Receiving/MessageSender+Encryption.swift

import SessionProtocolKit
import SessionUtilitiesKit

internal extension MessageSender {

    static func encryptWithSignalProtocol(_ plaintext: Data, associatedWith message: Message, for publicKey: String, using transaction: Any) throws -> Data {
        let storage = Configuration.shared.signalStorage
        let cipher = try SMKSecretSessionCipher(sessionResetImplementation: Configuration.shared.sessionRestorationImplementation,
            sessionStore: storage, preKeyStore: storage, signedPreKeyStore: storage, identityStore: Configuration.shared.identityKeyStore)
        let useFallbackEncryption: Bool = {
            if (message is SessionRequest) { return true }
            return !storage.containsSession(publicKey, deviceId: 1, protocolContext: transaction)
        }()
        let certificate = Configuration.shared.storage.getSenderCertificate(for: publicKey)
        return try cipher.throwswrapped_encryptMessage(recipientPublicKey: publicKey, deviceID: 1, paddedPlaintext: (plaintext as NSData).paddedMessageBody(),
            senderCertificate: certificate, protocolContext: transaction, useFallbackSessionCipher: useFallbackEncryption)
    }

    static func encryptWithSharedSenderKeys(_ plaintext: Data, for groupPublicKey: String, using transaction: Any) throws -> Data {
        // 1. ) Encrypt the data with the user's sender key
        guard let userPublicKey = Configuration.shared.storage.getUserPublicKey() else {
            SNLog("Couldn't find user key pair.")
            throw Error.noUserPublicKey
        }
        let (ivAndCiphertext, keyIndex) = try SharedSenderKeys.encrypt(plaintext, for: groupPublicKey, senderPublicKey: userPublicKey, using: transaction)
        let encryptedMessage = ClosedGroupCiphertextMessage(_throws_withIVAndCiphertext: ivAndCiphertext, senderPublicKey: Data(hex: userPublicKey), keyIndex: UInt32(keyIndex))
        // 2. ) Encrypt the result for the group's public key to hide the sender public key and key index
        let intermediate = try AESGCM.encrypt(encryptedMessage.serialized, for: groupPublicKey.removing05PrefixIfNeeded())
        // 3. ) Wrap the result
        return try SNProtoClosedGroupCiphertextMessageWrapper.builder(ciphertext: intermediate.ciphertext, ephemeralPublicKey: intermediate.ephemeralPublicKey).build().serializedData()
    }
}