Csharp 具有大字符串的对称加密返回相同的字符串但丢失 15 个字节

我一直在使用我使用SHA1编写的旧代码来处理SHA256或SHA512. 我是密码学领域的新手，我想知道有没有人能告诉我，为什么我在ENCRYPT方法中的输入值通过DECRYPT方法返回时会丢失1-5个字节.

我可以用短字符串运行这些方法，没有问题，但显然不会更大，例如16个字节+.

有问题的两种方法是:

    public string Decrypt(string data, EncryptionValue eV, string passPhrase)
{
    byte[] bytes = Encoding.ASCII.GetBytes(eV.InitVector);
    byte[] rgbSalt = Encoding.ASCII.GetBytes(eV.SaltValue);
    byte[] buffer = Convert.FromBase64String(data);
    byte[] rgbKey = new Rfc2898DeriveBytes(passPhrase, rgbSalt, eV.PassIterations, hash).GetBytes(eV.KeySize / 8);

    var managed = Aes.Create("AesManaged");
    managed.Padding = PaddingMode.PKCS7;
    managed.Mode = CipherMode.CBC;
    ICryptoTransform transform = managed.CreateDecryptor(rgbKey, bytes);
    MemoryStream stream = new(buffer);
    CryptoStream stream2 = new(stream, transform, CryptoStreamMode.Read);
    byte[] buffer5 = new byte[buffer.Length];
    int count = stream2.Read(buffer5, 0, buffer5.Length);
    stream.Close();
    stream2.Close();
    return Encoding.UTF8.GetString(buffer5, 0, count);
}
public string Encrypt(string data, EncryptionValue eV, string passPhrase)
{
    byte[] bytes = Encoding.ASCII.GetBytes(eV.InitVector);
    byte[] rgbSalt = Encoding.ASCII.GetBytes(eV.SaltValue);
    byte[] buffer = Encoding.UTF8.GetBytes(data);
    byte[] rgbKey = new Rfc2898DeriveBytes(passPhrase, rgbSalt, eV.PassIterations, hash).GetBytes(eV.KeySize / 8);

    var managed = Aes.Create("AesManaged");
    managed.Padding = PaddingMode.PKCS7;
    
    managed.Mode = CipherMode.CBC;
    ICryptoTransform transform = managed.CreateEncryptor(rgbKey, bytes);
    MemoryStream stream = new();
    CryptoStream stream2 = new(stream, transform, CryptoStreamMode.Write);
    stream2.Write(buffer, 0, buffer.Length);
    stream2.FlushFinalBlock();
    byte[] inArray = stream.ToArray();
    stream.Close();
    stream2.Close();
    return Convert.ToBase64String(inArray);
}

加密值类别包含随机化的值，这不是这里的问题，但我还是要在这里发布它:

 public int PassIterations { get; set; }
 public int KeySize { get; set; }
 public string InitVector { get; set; }
 public string SaltValue { get; set; }

在我的所有测试中，迭代次数都在1000次左右.我已经做了越来越多的测试. KeySize始终为256或128， InitVector="~1B2C3D4e5F6g7H8"；

我运行了一些测试，正如我所说的，较小的字符串是可以的，但我希望它能够存储至少120个字节.我以为这能行得通？