82 lines
3.5 KiB
C#
82 lines
3.5 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Text;
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namespace Duplicati.Encryption
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{
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/// <summary>
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/// Implements AES encryption
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/// </summary>
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public class AESEncryption : EncryptionBase, IEncryption
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{
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/// <summary>
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/// The AES instance
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/// </summary>
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private System.Security.Cryptography.Rijndael m_instance;
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/// <summary>
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/// Constructs a new AES encryption/decyption instance
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/// </summary>
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/// <param name="key">The key used for encryption. The key gets stretched through SHA hashing to fit the key size requirements</param>
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public AESEncryption(string key)
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{
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m_instance = System.Security.Cryptography.Rijndael.Create();
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System.Security.Cryptography.SHA256 sha = System.Security.Cryptography.SHA256.Create();
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int len = m_instance.IV.Length + m_instance.Key.Length;
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System.IO.MemoryStream ms = new System.IO.MemoryStream();
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//We stretch the key material by issuing cascading hash operations.
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//This somewhat alters the characteristics of the key, but as long
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//as the hashing is cryptographically safe and does not induce aliasing
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//with the encryption, it does not reduce the strength of the encryption
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byte[] tmp = System.Text.Encoding.UTF8.GetBytes(key);
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while (ms.Length < len)
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{
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if (!sha.CanReuseTransform)
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sha = System.Security.Cryptography.SHA256.Create();
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sha.Initialize();
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tmp = sha.ComputeHash(tmp);
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ms.Write(tmp, 0, (int)Math.Min(tmp.Length, len - ms.Length));
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}
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byte[] realkey = new byte[m_instance.Key.Length];
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byte[] iv = new byte[m_instance.IV.Length];
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ms.Position = 0;
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if (ms.Read(iv, 0, iv.Length) != iv.Length)
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throw new Exception("Bad key stretch");
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if (ms.Read(realkey, 0, realkey.Length) != realkey.Length)
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throw new Exception("Bad key stretch");
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ms.Dispose();
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m_instance.IV = iv;
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m_instance.Key = realkey;
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m_instance.Mode = System.Security.Cryptography.CipherMode.CBC;
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}
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#region IEncryption Members
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public override void Encrypt(System.IO.Stream input, System.IO.Stream output)
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{
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if (m_instance.Mode == System.Security.Cryptography.CipherMode.ECB)
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throw new Exception("Useless encryption detected");
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System.Security.Cryptography.ICryptoTransform ct = m_instance.CreateEncryptor();
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using (System.Security.Cryptography.CryptoStream cs = new System.Security.Cryptography.CryptoStream(input, ct, System.Security.Cryptography.CryptoStreamMode.Write))
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Core.Utility.CopyStream(cs, output);
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}
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public override void Decrypt(System.IO.Stream input, System.IO.Stream output)
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{
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if (m_instance.Mode == System.Security.Cryptography.CipherMode.ECB)
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throw new Exception("Useless encryption detected");
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System.Security.Cryptography.ICryptoTransform ct = m_instance.CreateDecryptor();
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using (System.Security.Cryptography.CryptoStream cs = new System.Security.Cryptography.CryptoStream(input, ct, System.Security.Cryptography.CryptoStreamMode.Read))
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Core.Utility.CopyStream(cs, output);
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}
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#endregion
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}
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}
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