C# 文件加密解密 SHA256

/// <summary>
/// 加密文件随机数生成
/// </summary>
private static RandomNumberGenerator rand = new RNGCryptoServiceProvider();
private const int BUFFER_SIZE = 128 * 1024;
private const ulong FC_TAG = 0xFC010203040506CF;
/// <summary>
/// 生成指定长度的随机Byte数组
/// </summary>
/// <param name="count">Byte数组长度</param>
/// <returns>随机Byte数组</returns>
private static byte[] GenerateRandomBytes(int count)
{
byte[] bytes = new byte[count];
//产生随机序列
rand.GetBytes(bytes);
return bytes;
}
/// <summary>
/// 创建Rijndael SymmetricAlgorithm
/// </summary>
/// <param name="password">密码</param>
/// <param name="salt"></param>
/// <returns>加密对象</returns>
private static SymmetricAlgorithm CreateRijndael(string password, byte[] salt)
{
PasswordDeriveBytes pdb = new PasswordDeriveBytes(password, salt, "SHA256", 1000);

SymmetricAlgorithm sma = Rijndael.Create();
sma.KeySize = 256;
sma.Key = pdb.GetBytes(16);
sma.Padding = PaddingMode.PKCS7;
return sma;
}
public static void EncryptFile(string inFile, string outFile, string password)
{
using (FileStream fin = File.OpenRead(inFile),
fout = File.OpenWrite(outFile))
{
long lSize = fin.Length; // 输入文件长度
int size = (int)lSize;
byte[] bytes = new byte[BUFFER_SIZE]; // 缓存
int read = -1; // 输入文件读取数量
int value = 0;

// 获取IV和salt
//密钥salt在加密算法中主要被设计用来防止“字典攻击”。字典攻击也是一种穷举的暴力破解法。字典中会假设一定数量的密码值，
//攻击者会尝试用这些密码来解密密文。Salt是在密钥导出之前在密码末尾引入的随机字节，它使这类攻击变得非常困难
//初始化向量IV在加密算法中起到的也是增强破解难度的作用。在加密过程中，如果遇到相同的数据块，其加密出来的结果也一致，相对就会容易破解。
//加密算法在加密数据块的时候，往往会同时使用密码和上一个数据块的加密结果。因为要加密的第一个数据块显然不存在上一个数据块，所以这个初始化向量就是被设计用来当作初始数据块的加密结果。
byte[] IV = GenerateRandomBytes(16);
byte[] salt = GenerateRandomBytes(16);

// 创建加密对象
SymmetricAlgorithm sma = CreateRijndael(password, salt);
sma.IV = IV;

// 在输出文件开始部分写入IV和salt
fout.Write(IV, 0, IV.Length);
fout.Write(salt, 0, salt.Length);

// 创建散列加密
HashAlgorithm hasher = SHA256.Create();
//     定义将数据流链接到加密转换的流。
using (CryptoStream cout = new CryptoStream(fout, sma.CreateEncryptor(), CryptoStreamMode.Write),
chash = new CryptoStream(Stream.Null, hasher, CryptoStreamMode.Write))
{
BinaryWriter bw = new BinaryWriter(cout);
bw.Write(lSize);

bw.Write(FC_TAG);

// 读写字节块到加密流缓冲区
while ((read = fin.Read(bytes, 0, bytes.Length)) != 0)
{
cout.Write(bytes, 0, read);
chash.Write(bytes, 0, read);
value += read;
}
// 关闭加密流
chash.Flush();
chash.Close();

// 读取散列
//在 chash 获取散列密钥
byte[] hash = hasher.Hash;

// 输入文件写入散列
cout.Write(hash, 0, hash.Length);

// 关闭文件流
cout.Flush();
cout.Close();
}
}
}
/// <summary>
/// 解密文件
/// </summary>
/// <param name="inFile">待解密文件</param>
/// <param name="outFile">解密后输出文件</param>
/// <param name="password">解密密码</param>
public static void DecryptFile(string inFile, string outFile, string password)
{
// 创建打开文件流
using (FileStream fin = File.OpenRead(inFile),
fout = File.OpenWrite(outFile))
{
int size = (int)fin.Length;
byte[] bytes = new byte[BUFFER_SIZE];
int read = -1;
int value = 0;
int outValue = 0;

byte[] IV = new byte[16];
fin.Read(IV, 0, 16);
byte[] salt = new byte[16];
fin.Read(salt, 0, 16);

SymmetricAlgorithm sma = CreateRijndael(password, salt);
sma.IV = IV;

value = 32;
long lSize = -1;

// 创建散列对象, 校验文件
HashAlgorithm hasher = SHA256.Create();

using (CryptoStream cin = new CryptoStream(fin, sma.CreateDecryptor(), CryptoStreamMode.Read),
chash = new CryptoStream(Stream.Null, hasher, CryptoStreamMode.Write))
{
// 读取文件长度
BinaryReader br = new BinaryReader(cin);
lSize = br.ReadInt64();
ulong tag = br.ReadUInt64();

if (FC_TAG != tag)
throw new Exception("文件被破坏");

long numReads = lSize / BUFFER_SIZE;

long slack = (long)lSize % BUFFER_SIZE;

for (int i = 0; i < numReads; ++i)
{
read = cin.Read(bytes, 0, bytes.Length);
fout.Write(bytes, 0, read);
chash.Write(bytes, 0, read);
value += read;
outValue += read;
}

if (slack > 0)
{
read = cin.Read(bytes, 0, (int)slack);
fout.Write(bytes, 0, read);
chash.Write(bytes, 0, read);
value += read;
outValue += read;
}

chash.Flush();
chash.Close();

fout.Flush();
fout.Close();

byte[] curHash = hasher.Hash;

// 获取比较和旧的散列对象
byte[] oldHash = new byte[hasher.HashSize / 8];
read = cin.Read(oldHash, 0, oldHash.Length);
if ((oldHash.Length != read) || (!CheckByteArrays(oldHash, curHash)))
throw new Exception("文件被破坏");
}

if (outValue != lSize)
throw new Exception("文件大小不匹配");
}
}
/// <summary>
/// 检验两个Byte数组是否相同
/// </summary>
/// <param name="b1">Byte数组</param>
/// <param name="b2">Byte数组</param>
/// <returns>true－相等</returns>
private static bool CheckByteArrays(byte[] b1, byte[] b2)
{
if (b1.Length == b2.Length)
{
for (int i = 0; i < b1.Length; ++i)
{
if (b1[i] != b2[i])
return false;
}
return true;
}
return false;
}