SystemExtensions/SystemExtensions.NetStandard.Security/Encryption/AesEncrypter.cs

using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Threading.Tasks;
using System.Security.Utilities;

namespace System.Security.Encryption;

public sealed class AesEncrypter : ISymmetricEncrypter, IDisposable
{
    private readonly Aes aes;

    public AesEncrypter()
    {
        this.aes = Aes.Create();
    }

    public AesEncrypter(Aes aes)
    {
        this.aes = aes;
    }

    public async Task<string> Decrypt(string key, string iv, string value)
    {
        using var valueStream = BytesToStream(StringToBytes(value));
        using var decryptedStream = await this.DecryptInternal(StringToBytes(key), StringToBytes(iv), valueStream).ConfigureAwait(false);
        return StreamToString(decryptedStream);
    }

    public async Task<string> Decrypt(byte[] key, byte[] iv, string value)
    {
        using var valueStream = BytesToStream(StringToBytes(value));
        using var decryptedStream = await this.DecryptInternal(key, iv, valueStream).ConfigureAwait(false);
        return StreamToString(decryptedStream);
    }

    public async Task<byte[]> Decrypt(string key, string iv, byte[] value)
    {
        using var valueStream = BytesToStream(value);
        using var decryptedStream = await this.DecryptInternal(StringToBytes(key), StringToBytes(iv), valueStream).ConfigureAwait(false);
        return StreamToBytes(decryptedStream);
    }

    public async Task<byte[]> Decrypt(byte[] key, byte[] iv, byte[] value)
    {
        using var valueStream = BytesToStream(value);
        using var decryptedStream = await this.DecryptInternal(key, iv, valueStream).ConfigureAwait(false);
        return StreamToBytes(decryptedStream);
    }

    public async Task<Stream> Decrypt(string key, string iv, Stream value)
    {
        return await this.DecryptInternal(StringToBytes(key), StringToBytes(iv), value).ConfigureAwait(false);
    }

    public async Task<Stream> Decrypt(byte[] key, byte[] iv, Stream value)
    {
        return await this.DecryptInternal(key, iv, value).ConfigureAwait(false);
    }

    public async Task<string> Encrypt(string key, string iv, string value)
    {
        using var valueStream = BytesToStream(StringToBytes(value));
        using var encryptedStream = await this.EncryptInternal(StringToBytes(key), StringToBytes(iv), valueStream).ConfigureAwait(false);
        return StreamToString(encryptedStream);
    }

    public async Task<string> Encrypt(byte[] key, byte[] iv, string value)
    {
        using var valueStream = BytesToStream(StringToBytes(value));
        using var encryptedStream = await this.EncryptInternal(key, iv, valueStream).ConfigureAwait(false);
        return StreamToString(encryptedStream);
    }

    public async Task<byte[]> Encrypt(string key, string iv, byte[] value)
    {
        using var valueStream = BytesToStream(value);
        using var encryptedStream = await this.EncryptInternal(StringToBytes(key), StringToBytes(iv), valueStream).ConfigureAwait(false);
        return StreamToBytes(encryptedStream);
    }

    public async Task<byte[]> Encrypt(byte[] key, byte[] iv, byte[] value)
    {
        using var valueStream = BytesToStream(value);
        using var encryptedStream = await this.EncryptInternal(key, iv, valueStream).ConfigureAwait(false);
        return StreamToBytes(encryptedStream);
    }

    public async Task<Stream> Encrypt(string key, string iv, Stream value)
    {
        return value is null
            ? throw new ArgumentNullException(nameof(value))
            : await this.EncryptInternal(StringToBytes(key), StringToBytes(iv), value).ConfigureAwait(false);
    }

    public async Task<Stream> Encrypt(byte[] key, byte[] iv, Stream value)
    {
        return value is null
            ? throw new ArgumentNullException(nameof(value))
            : await this.EncryptInternal(key, iv, value).ConfigureAwait(false);
    }

    public Stream GetEncryptionStream(string key, string iv, Stream outStream)
    {
        return this.GetEncryptionStreamInternal(StringToBytes(key), StringToBytes(iv), outStream);
    }

    public Stream GetEncryptionStream(byte[] key, byte[] iv, Stream outStream)
    {
        return this.GetEncryptionStreamInternal(key, iv, outStream);
    }

    public Stream GetDecryptionStream(string key, string iv, Stream inStream)
    {
        return this.GetDecryptionStreamInternal(StringToBytes(key), StringToBytes(iv), inStream);
    }

    public Stream GetDecryptionStream(byte[] key, byte[] iv, Stream inStream)
    {
        return this.GetDecryptionStreamInternal(key, iv, inStream);
    }

    private async Task<Stream> EncryptInternal(byte[] key, byte[] iv, Stream toEncryptStream)
    {
        if (key.Length < 32)
        {
            throw new ArgumentException($"{nameof(key)} must be at least 32 bytes");
        }

        if (iv.Length < 16)
        {
            throw new ArgumentException($"{nameof(iv)} must be at least 16 bytes");
        }

        key = key.Take(32).ToArray();
        iv = iv.Take(16).ToArray();


        var encryptedMemoryStream = new MemoryStream();
        using var cryptoStream = this.GetEncryptionStreamInternal(key, iv, encryptedMemoryStream);
        await toEncryptStream.CopyToAsync(cryptoStream).ConfigureAwait(false);
        if (!cryptoStream.HasFlushedFinalBlock)
        {
            cryptoStream.FlushFinalBlock();
        }

        encryptedMemoryStream.Position = 0;
        return encryptedMemoryStream;
    }

    private async Task<Stream> DecryptInternal(byte[] key, byte[] iv, Stream toDecryptStream)
    {
        if (key.Length < 32)
        {
            throw new ArgumentException($"{nameof(key)} must be at least 32 bytes");
        }

        if (iv.Length < 16)
        {
            throw new ArgumentException($"{nameof(iv)} must be at least 16 bytes");
        }

        key = key.Take(32).ToArray();
        iv = iv.Take(16).ToArray();


        var decryptedMemoryStream = new MemoryStream();
        using var cryptoStream = this.GetDecryptionStreamInternal(key, iv, toDecryptStream);
        await cryptoStream.CopyToAsync(decryptedMemoryStream).ConfigureAwait(false);
        if (!cryptoStream.HasFlushedFinalBlock)
        {
            cryptoStream.FlushFinalBlock();
        }

        decryptedMemoryStream.Position = 0;
        return decryptedMemoryStream;
    }

    private CryptoStream GetEncryptionStreamInternal(byte[] key, byte[] iv, Stream encryptedStream)
    {
        var crypto = this.aes.CreateEncryptor(key, iv);
        var cryptoStream = new NotClosingCryptoStream(encryptedStream, crypto, CryptoStreamMode.Write);
        return cryptoStream;
    }

    private CryptoStream GetDecryptionStreamInternal(byte[] key, byte[] iv, Stream encryptedStream)
    {
        var crypto = this.aes.CreateDecryptor(key, iv);
        var cryptoStream = new NotClosingCryptoStream(encryptedStream, crypto, CryptoStreamMode.Read);
        return cryptoStream;
    }

    private static byte[] StreamToBytes(Stream value)
    {
        value.Position = 0;
        var buffer = new byte[1024];
        using var ms = new MemoryStream();
        var read = -1;
        do
        {
            read = value.Read(buffer, 0, buffer.Length);
            ms.Write(buffer, 0, read);
        } while (read > 0);
        return ms.ToArray();
    }

    private static string StreamToString(Stream value)
    {
        return Convert.ToBase64String(StreamToBytes(value));
    }

    private static byte[] StringToBytes(string value)
    {
        return Convert.FromBase64String(value);
    }

    private static Stream BytesToStream(byte[] value)
    {
        return new MemoryStream(value);
    }

    public void Dispose()
    {
        this.aes.Dispose();
    }
}