In MySQL i can do
SELECT * FROM table WHERE MD5(column) = 'blablabla';
But how do i do that with NHibernate and Criteria functions?
I got a value alrady as md5 but the column in the database is not md5 hashed...
I working in C#.
Some ideas?
In Java, you can use Expression.Sql, the same should work in C#, something like:
var table = session.CreateCriteria(typeof(Table))
.Add(Expression.Sql("MD5(column)= ?", value, NHibernateUtil.String))
.UniqueResult<Table>();
where value is the hex-encoded value of your MD5 hash.
Although, one word of caution - if the value stored in the database is the user's password, then your design is flawed and insecure. You should only store salted, hashed passwords in the database. No, you shouldn't even do that, you should right away use bcrypt, scrypt or PBKDF2 for that.
Related
I have the following issue: I am currently working on a ASP .net core entity framework backend and have the problem that I need to use a Custom Method in LINQ Query and getting a error when doing this. I
researched and found out that it is possible to write custom functions, that will be translated to sql, but I think that there is not a big scope for doing this. (e.g: SQL will not be able to use Libaries and hash strings).
Another way that I have heard of ist to convert my Database to a Enumberale and then apply my Custom Methods on it, which works, but is not that performant, because I am saving my whole Database in my memory, which gets very slow when having a huge amount of data. So my question is, if there is a performant solution to perform custom methods in LINQ queries?
My detailed problem is, that I have saved my salted passwords hashed in my database and when someone want s to log in to his account I have to compare the password in the database with the salt + user password input, that has to get hashed in my where clause. It would work if I wouldnt use salts, because then, I would only have to hash the user input, which is not column of the database.
What you should do is - calculate the hash and salt in the backend, and use the computed hash in your WHERE statement. In this case you don't need to call your methods from SQL equally you don't need to pull entire db (or table) into memory to compute hash.
As I don't know your code, the pseudo-code approach would be:
var user = service.GetUserByEmail(email);
if (user == null) {
//Invalid User
}
var hash = ComputeHash(user.Salt, inputPwd);
if(user.PasswordHash == hash) {
//User is logged in
} else {
//Invalid Password or email
}
How to convert a hashed password in text string in SQL Server 2008?
I want to know the password of user which is stored in SQL Server as hash password. How to convert hashed password to normal text?
thats generally not how it works. Password checks are done on the following principal
Password -> encryption -> saved
then when user enters a password you reencrypt it, and compare the new encrypted to the old, if its the same then you got the right password you can enter. This stops people "finding out" other peoples passwords and keeps systems secure. Which is why often brute force password cracking is needed to get into things.
If you can unencrypt it - then there was no point storing it encrypted in the first place.
you cant send a string and decrypt it, because DecryptByPassPhrase function expects a varbinary parameter.
here is a small example
declare #encrypt varbinary(200)
select #encrypt = EncryptByPassPhrase('key', 'abc' )
select #encrypt
select convert(varchar(100),DecryptByPassPhrase('key', #encrypt ))
I was reading this article about hashing passwords when I came to this part:
To Validate a Password
Retrieve the user's salt and hash from the database.
Prepend the salt to the given password and hash it using the same
hash function.
Compare the hash of the given password with the hash from the
database. If they match, the password is correct. Otherwise, the
password is incorrect.
But I am a little confused with the flow this would follow, for example lets assume I have a database with a user table with id,name,password and email and in order to login to some app I need to input my email and password.
Following the the steps above, I first need to get the salt+hashed password of said user stored in the database.
Question:
Assuming I am using a simple stored procedure would the only way be to do it like this...
CREATE PROCEDURE [dbo].[sp_validate_user]
#us_email VARCHAR (MAX)
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
-- Insert statements for procedure here
SELECT us_id,
us_name,
us_pass,
us_email
FROM Users
WHERE us_email = #us_email
END
Then following step two and three:
public static bool ValidatePassword(string inputPassword, string storedPassword)
{
// Extract the parameters from the hash
char[] delimiter = { ':' };
string[] split = storedPassword.Split(delimiter);
int iterations = Int32.Parse(split[ITERATION_INDEX]);
byte[] salt = Convert.FromBase64String(split[SALT_INDEX]);
byte[] hash = Convert.FromBase64String(split[PBKDF2_INDEX]);
byte[] testHash = PBKDF2(inputPassword, salt, iterations, hash.Length);
return SlowEquals(hash, testHash);
}
My concern comes from the fact that if I am creating objects with the data pulled from the table, doesn't that make the information within vulnerable somehow?
Also does that mean that the only way to use this validation is pulling all the user's information based only on a username/email just to check in runtime if the input password and the hashed one match and then letting said user access the information?
I'm sorry if this sounds confusing but any insight would be great.
It looks like you may be thinking of it backwards. The salt is added to the cleartext password before passing to the hash function. Store the end result in the database.
Commonly, the salt is the username. Something unique to each user to thwart dictionary attacks. (A dictionary attack relies on the economy of scale by cracking one password and then looking for other instances of the same crypto-text. It used to work especially well on very large user databases like well known sites that have millions of users, but hopefully those sites use proper salting and key derivation nowadays).
So for username u, password p, assume SHA2 is hash function. Concatenate u + p to get a salted value, then hash it.
hashtext = SHA2(u + p) // in this case, + is concatenate
hashtext is what you store in the database.
For the login, user enters his username u2 and password p2:
tryhash = SHA2(u2 + p2)
Query database for a user record matching u2, with password hashtext of tryhash
Lets say you have an MVC action receiving loginViewModel which is populated with cleartext email or username as well as cleartext password, entered from the page:
var loginUser = new User(loginViewModel);
CalcHash(loginUser);
var realUser = users.Find(loginUser.username);
if(realUser.HashPassword == loginUser.HashPassword)
// success
While it is also possible to add the hashed password as a second argument to your Data Access method, ie. users.Find(username, hashPass), it is usually not done this way, because you need to access the user record even if the password fails, in order to increment password failure count and lockout the account.
The article covers ASP.NET (C#) Password Hashing Code but you seem to want to use a database?
You have three things to worry about; the unique key for the user (username), your chosen hashing algorithm and adding a salt to the password attempt (prevents rainbow table attacks).
To validate a password you should create a sql stored procedure that accepts the username and password attempt as parameters. This data is in plain text and has been entered into the web form, passed to the web server and will be passed into the database server via the stored procedure.
The stored procedure will do the following;
Lookup the data row for user based on matching the username parameter with the username field and
select the stored salt field
Append the salt from (1) to the password parameter and hash the result
Lookup the data row for the user based on matching the username parameter with the username field
and the hash result from (2) with the hashed password field.
If there is no row found the password hashes don't match and are wrong so return a suitable error code
If there is a row found return the useful user data i.e. First Name, Address
If the stored procedure handles all this then the web server never needs to know what the salt is or the hashing algorithm. At no point does the hash result or the salt get transmitted out of the database server.
I think you understood it correctly, this is the usual workflow:
Get the password-hash by username SELECT password_hash FROM user WHERE email=?.
Extract the salt from the password_hash, or get the salt from a separate field.
Calculate the hash of the entered password with the extracted salt and compare the hashes.
Validating the password cannot be done in a single query, because you first have to extract the salt. Appropriate hash functions like PBKDF2, BCrypt or SCrypt are often not supported by the database system, so you have to do the validation in your code. Additionally to the salt you also have to store other parameters like the cost factor and the algorithm (to be future-proof), so it is a good idea to store all these parameters in the same database field.
The salt should be a random string of at least 20 characters, so it is not safe to use the username as salt, or to derrive the salt from other information.
I have spent the past hour reading up on salting and still don't understand how it is achieved. Forgive me if im wrong, but the way I am thinking of salting is, storing an ArrayList of random strings for example 100 strings. Now when a user registers, a method gets a random string from the array list and retrieves the index of the string within the array to insert into my DB, it then applies this random string to the password the user entered and then hashes the whole string and stores into the DB.
Now when the user logs in it will retrieve the index for the ArrayList of random strings, then applies it to the entered password to then hash the whole string and compare the 2 passwords.
Is this a good way of salting? Is this classed as salting?
It's better to have unique salts for each user/password hash instead of reusing a limited set of 100 salts.
The reason is because of the way hackers attempt to compromise a database full of passwords once they get a hold of it, in particular using rainbow tables to find known values shared between multiple users.
For example (pseudo-code):
This is bad because once a hacker cracks the first password hash, both users are compromised.
//BAD WAY
var nonUniqueSalt = "some salt value";
var userPass1 = "P#ssword!";
var userPass2 = "P#ssword!";
//Bad! This will be true!
var isSame = (DoHash(userPass1 + nonUniqueSalt) == DoHash(userPass2 + nonUniqueSalt));
This way is better, because the salts are different even if the passwords are the same, so the hacker can't use rainbow tables and is forced to compromise each user's password individually.
//BETTER WAY
var uniqueSalt1 = "unique salt 1";
var userPass1 = "P#ssword!";
var uniqueSalt2 = "unique salt 2";
var userPass2 = "P#ssword!";
//Better! This will be false.
var isSame = (DoHash(userPass1 + uniqueSalt1) == DoHash(userPass2 + uniqueSalt2));
As far as the salting "algorithm" some users mentioned in comments, you don't REALLY need to worry about it too much aside from trying to make the salt unique to each user (because of the reasons described above).
In practice, whatever salt you use will need to be stored in the DB alongside the password hash, so once a hacker has the database, he'll have the value you used for a salt no matter how you go about deriving it.
As such, using a salt based on something like Guid.NewGuid().ToString() is sufficient for simply having unique values for each login.
The scenario is that I want to encrypt finance numbers in a column with a data type of int in a sql server table.
It is a big app so it is difficult to change the table column data type from int to any other data type.
I'm using sql server 2005 and asp.net C#.
Is there a two-way encryption method for a column with a data type of int?
Could I use a user-defined-function in sql server 2005 or a possibly a C# method?
I'm sorry but I simply can't see the rationale for encrypting numbers in a database. If you want to protect the data from prying eyes, surely SQL Server has security built into it, yes?
In that case, protect the database with its standard security. If not, get a better DBMS (though I'd be surprised if this were necessary).
If you have bits of information from that table that you want to make available (like some columns but not others), use a view, or a trigger to update another table (less secured), or a periodic transfer to that table.
XOR?
:)
Hmm, need more text...
There are a few two way encryption schemes available in .Net.
Simple insecure two-way "obfuscation" for C#
You can either convert the integer to it's byte array equivalent or convert it to a base-64 string and encrypt that.
Well, every injective, surjective function from int to int can be used as a way to "encode" an integer.
You could build such a function by creating a random array with 65536 items with no duplicate entries und using f(i) = a[i]. To "decode" your int you simply create another array with b[i] = x | a[x] = i.
As the others have mentioned, this may not be what you REALLY want to do. =)
Edit: Check out Jim Dennis' comment!
You might want to look at format preserving encryption.