ParameterEncryptionAlgorithm.cs

using System;
using System.Text;
using System.Threading.Tasks;
using Waher.Networking.XMPP.P2P.SymmetricCiphers;
using Waher.Security;
 
namespace Waher.Networking.XMPP.Contracts
{
    public class ParameterEncryptionAlgorithm : IParameterEncryptionAlgorithm
    {
        private readonly ContractsClient client;
        private readonly SymmetricCipherAlgorithms algorithm;
        private readonly IE2eSymmetricCipher instance;
        private readonly byte[] key;
 
        private ParameterEncryptionAlgorithm(SymmetricCipherAlgorithms Algorithm,
            IE2eSymmetricCipher Instance, byte[] Key, ContractsClient Client)
        {
            this.algorithm = Algorithm;
            this.instance = Instance;
            this.key = Key;
            this.client = Client;
        }
 
        public byte[] Key => this.key;
 
        public SymmetricCipherAlgorithms Algorithm => this.algorithm;
 
        public static Task<ParameterEncryptionAlgorithm> Create(SymmetricCipherAlgorithms Algorithm, ContractsClient Client)
        {
            return Create(null, Algorithm, Client);
        }
 
        public static async Task<ParameterEncryptionAlgorithm> Create(string ContractId, SymmetricCipherAlgorithms DefaultAlgorithm,
            ContractsClient Client)
        {
            string CreatorJid = Client.Client.BareJID;
            byte[] Key = null;
 
            if (!string.IsNullOrEmpty(ContractId))
            {
                Tuple<SymmetricCipherAlgorithms, string, byte[]> T = await Client.TryLoadContractSharedSecret(ContractId);
 
                if (!(T.Item3 is null))
                {
                    DefaultAlgorithm = T.Item1;
                    CreatorJid = T.Item2;
                    Key = T.Item3;
                }
            }
 
            return await Create(ContractId, DefaultAlgorithm, Client, CreatorJid, Key);
        }
 
        public static async Task<ParameterEncryptionAlgorithm> Create(string ContractId, SymmetricCipherAlgorithms Algorithm,
            ContractsClient Client, string CreatorJid, byte[] Key)
        {
            IE2eSymmetricCipher Instance = E2eSymmetricCipher.Create(Algorithm);
 
            if (Key is null)
            {
                Key = Instance.GenerateKey();
 
                if (!string.IsNullOrEmpty(ContractId))
                    await Client.SaveContractSharedSecret(ContractId, CreatorJid, Key, Algorithm, false);
            }
 
            return new ParameterEncryptionAlgorithm(Algorithm, Instance, Key, Client);
        }
 
        public byte[] Encrypt(string ParameterName, string ParameterType, uint ParameterIndex, string CreatorJid, byte[] ContractNonce,
            string ClearText)
        {
            byte[] Data;
 
            Data = new byte[this.key.Length + ContractNonce.Length + 4];
            int c = this.key.Length;
            int d = ContractNonce.Length;
 
            Buffer.BlockCopy(this.key, 0, Data, 0, c);
            Buffer.BlockCopy(ContractNonce, 0, Data, c, d);
            Buffer.BlockCopy(BitConverter.GetBytes(ParameterIndex), 0, Data, c + d, 4);
 
            Data = Hashes.ComputeSHA256Hash(Data);
 
            int SuffixLength = Data[0];
 
            if (ClearText is null)
                Data = new byte[SuffixLength];
            else
            {
                int Prefix = -1;
                int i, j;
 
                for (i = 1, c = Data.Length; i < c; i++)
                {
                    if ((j = Data[i]) != 0)
                    {
                        Prefix = j;
                        break;
                    }
                }
 
                if (Prefix < 0)
                    Prefix = 1;
 
                byte[] Data2 = Encoding.UTF8.GetBytes(ClearText);
                c = Data2.Length;
 
                Data = new byte[1 + c + SuffixLength];
 
                Data[0] = (byte)Prefix;
                Buffer.BlockCopy(Data2, 0, Data, 1, c);
            }
 
            byte[] IV = this.instance.GetIV(ParameterName, ParameterType, CreatorJid,
                Convert.ToBase64String(ContractNonce), ParameterIndex);
            byte[] AssociatedData = Encoding.UTF8.GetBytes(ParameterName);
 
            byte[] Result = this.instance.Encrypt(Data, this.key, IV, AssociatedData, E2eBufferFillAlgorithm.Zeroes);
 
            return Result;
        }
 
        public string Decrypt(string ParameterName, string ParameterType, uint ParameterIndex, string CreatorJid, byte[] ContractNonce,
            byte[] CipherText)
        {
            byte[] IV = this.instance.GetIV(ParameterName, ParameterType, CreatorJid, Convert.ToBase64String(ContractNonce), ParameterIndex);
            byte[] AssociatedData = Encoding.UTF8.GetBytes(ParameterName);
            byte[] Data = this.instance.Decrypt(CipherText, this.key, IV, AssociatedData);
 
            if (Data.Length == 0 || Data[0] == 0)
                return null;
 
            int c = Data.Length - 1;
 
            while (c >= 0 && Data[c] == 0)
                c--;
 
            return Encoding.UTF8.GetString(Data, 1, c);
        }
    }
}