Password encryption and decription in asp.net

protected void btnsignup_Click(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["cnn"].ToString());
con.Open();
string pass = passencrypt(txtpassword.Text.Trim());
SqlCommand cmd = new SqlCommand("insert into userdetails values('" + txtusername.Text.Trim() + "','" + pass + "')", con);
cmd.ExecuteNonQuery();
txtusername.Text = ""; txtpassword.Text = "";
}
protected void btnrecoverpassword_Click(object sender, EventArgs e)
{
SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["cnn"].ToString());
con.Open();
SqlCommand cmd = new SqlCommand("select password from userdetails where username=" + session["uname"].Tostring(), con);
string pass =(string) cmd.ExecuteScalar();
pass = passdecrypt(pass);
}

private string passencrypt(string sData)
{
byte[] encData_byte = new byte[sData.Length];
encData_byte = System.Text.Encoding.UTF8.GetBytes(sData);
string encodedData = Convert.ToBase64String(encData_byte);
return encodedData;
}
public string passdecrypt(string sData)
{
System.Text.UTF8Encoding encoder = new System.Text.UTF8Encoding();
System.Text.Decoder utf8Decode = encoder.GetDecoder();
byte[] todecode_byte = Convert.FromBase64String(sData);
int charCount = utf8Decode.GetCharCount(todecode_byte, 0, todecode_byte.Length);
char[] decoded_char = new char[charCount];
utf8Decode.GetChars(todecode_byte, 0, todecode_byte.Length, decoded_char, 0);
string result = new String(decoded_char);
return result;
}