Question

How to Limit Encrypted Password Length

Asked by: sonashish

I am using form based authentication. I have login table where password field length is varchar(25). I want to store encrypted in password field. I review various good articles, some of them mentioned below

http://msdn.microsoft.com/en-us/library/system.web.security.formsauthentication.hashpasswordforstoringinconfigfile.aspx

http://www.dotnetspark.com/Forum/137-how-to-encrypt--decrypt-password-and-stored.aspx

All this codes are good but their encrypted password length are more than 25 character. My problem here I cant change the length password field. Please someone suggest How can I generate 25 character encrypted length?

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Asked On
2009-09-30 at 07:11:32ID24773633
Topics

.NET

,

Microsoft Visual C#.Net

,

Programming for ASP.NET

Participating Experts
2
Points
500
Comments
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Answers

 

by: copyPasteGhostPosted on 2009-09-30 at 07:14:28ID: 25459049

is there a reason why the password length in your DB can't be changed to 50?

a regular MD5 encryption is 32 characters...I've never heard of a 25 character encrypted string. Unless you want to write your own encryption...which a strongly suggested not to do.

CPG

 

by: sonashishPosted on 2009-09-30 at 08:53:41ID: 25460185

To change the password length in db, it is not easy for us. It is huge application and we have used password field in various aspx, pages and store procedure.

Please advise

 

by: copyPasteGhostPosted on 2009-09-30 at 08:56:58ID: 25460225

As long as you INCREASE the size it will not break anything. Decreasing is the problem.

if you are using linq or entites you may need to rebuild your db context. but if you are only using stored procedures you should be good.

CPG

 

by: sonashishPosted on 2009-09-30 at 09:07:04ID: 25460330

I find 1 discussion thread and tested. Seems to look good, but still I am not comfortable. Here is the url

http://www.dreamincode.net/forums/showtopic79233.htm

 

by: copyPasteGhostPosted on 2009-09-30 at 09:14:03ID: 25460401

I'm not sure of the thread here...

if you want to know how to do encryption and decryption here is another post..

http://www.experts-exchange.com/Programming/Languages/C_Sharp/Q_21694806.html

but the posts you mentioned in your question are good as well...

What exactly are you not comfortable with?

CPG

 

by: sonashishPosted on 2009-09-30 at 09:20:48ID: 25460468

COde mentioned in http://www.dreamincode.net/forums/showtopic79233.htm is not very secure. What is your opinion?

 

by: copyPasteGhostPosted on 2009-09-30 at 09:24:38ID: 25460512

right it sucks.

like my pervious post >>Unless you want to write your own encryption...which is strongly suggested not to do.

it's custom. but it's for a school project so I guess thats ok for that implementation.

You need to use something like rijndael encryption, AES. like the sample you had and also the link I just provided.

Let me know if you need further assistance.
CPG

 

by: m_KristianPosted on 2009-09-30 at 09:25:37ID: 25460520

If you use a hash function like SHA-1 to store the passwords, the generated digest will be 20 bytes long. You should be able to store that in your varchar(25).

Have a look at the snippet I included below which should illustrate what I mean. The method HashPasswordForStoring always returns a 20 character string which should be unique to the input you give it - as long as you make sure to specify the right input encoding as well, so there is no misinterpretation of the password before generating the SHA-1 digest.

I am using a single byte encoding (ISO-8859-1) to convert the digest into a string, as this should ensure that each of the 20 bytes is translated into a single unique character. If you use the same approach when comparing passwords for login attempts, it should work.

public static class PasswordHelper
{
    private static Encoding digestEncoding = Encoding.GetEncoding("iso-8859-1");
 
    public static string HashPasswordForStoring(string password)
    {
        return HashPasswordForStoring(password, Encoding.UTF8);
    }
 
    public static string HashPasswordForStoring(string password, Encoding encoding)
    {
        byte[] passwordBytes = encoding.GetBytes(password);
 
        SHA1 hasher = SHA1Managed.Create();
        byte[] digest = hasher.ComputeHash(passwordBytes);
 
        return digestEncoding.GetString(digest);
    }
}

                                              
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by: sonashishPosted on 2009-09-30 at 09:57:22ID: 25460843

Kristian

How to decrypt it or reverse back to original password?

 

by: copyPasteGhostPosted on 2009-09-30 at 10:00:38ID: 25460874

with that encryption you will always need to encrypt the test string and compare it with the stored string . It's one way encryption. You can't decrypt it.

CPG

 

by: m_KristianPosted on 2009-09-30 at 10:13:04ID: 25461003

Right, this is hashing, not encryption. If you do it this way, you will only be able to use the stored values to evaluate login attempts - I didn't realize you needed to be able to get back the password in its original form. I would normally consider it good practice to store only the hashed versions of user passwords, but I may not fully understand your problem domain.

 

by: m_KristianPosted on 2009-09-30 at 10:39:37ID: 25461289

Another option might be to create a new table where you store the passwords in a column with the right datatype. Then you give each password in the new table a unique primary key and store that in the original table instead of the password itself. Similar to a traditional foreign key relationship.

That way you can look up the encrypted password string in the new table when you need it, using the key stored in the legacy table. It will mean a small (but most likely acceptable) performance penalty on the database level, as you have to do an extra query, however, it should avoid any compromises on security.

 

by: sonashishPosted on 2009-09-30 at 11:15:51ID: 25461664

Kristain

Here is the proceddure I have tested successfully. I am storing the hashing for password in password field. Now Once used enter his credentail like username and password (as plain text), first I converted password into hash value and then compared password  from sql table, if it mach thne he will be able to logged into table otherwise he will get erroe validation message.  I am also matchining Username, so there shuld be no duplicate value in the sql table.

What do you think is it correct approach?



 

by: m_KristianPosted on 2009-09-30 at 11:30:14ID: 25461808

That was the idea, yes. Doing it that way, it is not possible to obtain the original passwords, even if someone was to get access to your database. It should provide better security than storing encrypted strings, which could be decrypted by anyone who obtains the necessary keys, or is able to otherwise break the encryption.

You have to make sure to watch out for any encoding issues when storing the hashed password in the database. If the string is changed in any way, either when you first insert it or when you later retrieve it back, then the evalutation of credentials provided by the user will always fail.

It should be fairly simple to test I presume.

20120131-EE-VQP-002

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