Attention: Please read this topic carefully: This question is not seeking recommendations for books, tools, software libraries, and more. Instead, I am seeking for a method behind existing crypto in applications. A similar previous question got locked - IMHO due to a misunderstanding.
I am looking for the method (and maybe an implementation hint) how others obviously safe password on user drives in a safe way. For example on Windows: You can easily store the passwords of RemoteDesktop sessions w/o the need of entering a password when re-opening the session (even after re-starting your PC). Similar is the case for SMB connections or connections to SharePoint drives. My assumption is therefore, that there must be a safe way to safe passwords. This is what I want to understand. There are (closed source) tools around that store the password in some kind of hash in a file - which only works on that particular computer. This is what I am looking for but hopefully without the need to use excessive crypto libraries.
The background is that I am developing a native cross-platform app (esp. not a web-app but C++) that requires the input of a user name and password to connect to a proxy server. For convenience I want to store this sensitive information encrypted in the settings file of the app, which has INI-File format. Therefore, the file itself shall not be encrypted.
Does someone know an easy algorithm or method to do so?
I did find and tried algorithms based on SHA hashes and so one but they all either required a master password (which doesn't help because the point is exactly not to enter a password) or they literally used tons of crypto-libraries and non-cross-platform APIs which makes it hard to come to a cross-platform implementation.
All of these capabilities ultimately depend on a randomly generated master password that can only be read by a specific logged in user.
The safe way to store such a password is to encrypt it with a password that is generated from a hash of the user's login credentials.
If the user has multiple ways to log in, then a different copy of the master password must be stored for each login method, encrypted with a password generated from a hash of whatever credentials the user must supply for that particular login method. This generally requires OS support.
Often, implementations don't explicitly bother with this, instead relying on file system security to ensure that only the desired user can read the master password. In that case, though, you need to use disk encryption if you want to prevent the password from being accessed by super users or other means of bypassing file system security.
The disk encryption, though, will have its own master password encrypted with a login credential hash.
Related
I have a shell script which has password in clear text used in a command :
--username = 'USER'
--password ='abc100'
I dont want the password to be in clear text here in shell script. Is there a way i can keep this shell script password protected or to not pass the password in clear text and refer another file which is password protected ?
To solve this question well, it's really important to know how what this password represents and what sort of risks compromising it entails. It's also important to understand who has access to the machine on which this script and password file are stored, how the machines are set up, who needs to run this script, etc. It's really hard to give a good answer without understanding the full requirements and risks.
Assuming that compromising this password could have seriously negative repercussions and assuming that lots of people who should not have this password need to run this script, it would -- in my view -- be a mistake to store this password on the machines of everyone who needs to run this. You may want to consider having a smaller number of machines with much more limited access store this password and offer the functionality of the script through a webservice that uses an authentication mechanism such as OAuth (with Bearer tokens for automated access). Then the question becomes how do individual users have a script access the Bearer tokens needed to invoke the web service; although the Bearer tokens are also sensitive, they would at least be unique per user (giving a way to better detect compromise and abuse, though that is something you would still need to implement). In that sense, the question becomes similar to the original question, but with lower stakes.
Assuming that we are now talking about storing Bearer tokens, how you store it will depend on how many different users can access the same machine / filer system. For example, if many different people can have root access on the same machine, there is very little you can do. If there is one user per machine, however, and only that machine's owner can gain root, then you can use UNIX permissions to help limit / control access to files. For example, you could create a user+group that is dedicated to this specific script, have the script always run with that permission (e.g. via the sticky bit), and have the Bearer token information stored in a way that is readable only to that user/group (as a way to prevent other programs run by the same user from accessing that credential). In a setup where many people use the same machine but the people who can run as root can be trusted, you might just store the credential in a folder in the user's home directory that is accessible to only that user (and not readable/writable by the same group or other users); however, this does risk other programs run by that user reading the data. You could attempt to have the script encrypt/decrypt the content of the file on disk (e.g. embedding the key to encrypt/decrypt the data within the script), though unless the script were highly obfuscated and was regularly updated with this key rotated, that would do very little. You could also impose a short expiration on the bearer token so that the token need to be refreshed often as a mitigation measure to other programs misusing the token after it is no longer being used.
The following youtube video does a pretty good job at summarizing how EFS works.
For those interested in a summary of the contents of such windows I have attached
it below. However this leaves me with one question concerning security:
When a user logs on in Windows, presumably a hash is computed from the password
(or alternatively from the password plus the username and perhaps other data such
as a salt). When a user first creates a password, such hash must be stored somewhere
on the hard drive if I am not mistaken. At least, old Unix systems used to work in
such manner (with such has stored in /etc/passwd). Thus when a user logs on, the
password hash is computed and compared to what is stored in such file in order
to authenticate the user. If the hashes match, the user is logged in.
So far so good. If the above mechanism is the one used (on modern Windows systems),
this means that when someone hacks into a Window system, they can read such password hash,
and thus, using the special Microsoft symmetric encryption algorithm (as described below)
which is stored on the hard drive and thus can be learned by a hacker, the password hash
plus the Microsoft special symmetric algorithm plus knowledge of where the encrypted
private key is stored on the hard drive allows the hacker to decrypt it, thus obtaining
the private key. And once the private key is obtained of course, then all data encrypted
using the public key in the certificate can be decrypted by the hacker.
Can someone please point out the flaw in my reasoning?
Presumably the flaw is due to a misunderstanding of mine concerning
how Windows authentication is carried out.
Thanks.
http://www.youtube.com/watch?v=YxgWsa-slOU
Summary of the contents of the above video:
- EFS (available in the NTFS file system) is designed to allow users
to encrypt files and folders so that nobody except for the person
encrypting such file or folder can access it. Administrative accounts
on stolen machines can be created with minimal hacking knowledge, and
can thus gain access to virtually any files contained on the hard drive.
Symmetric key encryption algorithms work about 100 to 1000 times faster
than public key encryption algorithms.
right-click -> Properties -> General -> Advanced... -> Encrypt Contents
to Secure Data and click on Apply, (you can then choose between
encrypting just the file or encrypting the file and its parent folder
and then click on OK). Windows will turn the file green and we will
still have full access to the file. Once this someone logging in
with an administrator account will not be able to see the file.
You can in fact access the certificate manager with the "certmgr"
command, and from there you can view the contents of the
Personal -> Certificates application folder, which can
start out as empty. When we encrypt a file in the above
manner, a symmetric key called a DESX algorithm file encryption key (FEK)
is generated and then the certificate's public key is used to encrypt
the FEK and store it with the encrypted data. In the certificate contained
in the certificate store you can get access to the public key but not the
private key (the cerificate attests that user such and such are who they
say they are and displays the user's public key). The certificate also
points to the private key, but such private key is stored in a special
location on the hard drive, and is encrypted using a special Microsoft
symmetric key algorithm generated master key, where the master key is
generated using a hash component from the username and password of the
user every time the user logs on, and the resulting symmetric key is not
stored anywhere on the hard drive (i.e. it must be kept somewhere in memory).
The hash value that is used to access the private key, which unlocks the symmetric key, is not the same as the hash value that is stored (used for authentication). Both hashes are derived from the password, but they are not computed the same way. Neither are reversible, and they cannot be used interchangeably.
To access your files, they need you to either be logged in already, or they need your password.
Also note that EFS normally designates the administrator or domain administrator as the "recovery agent". When the private key is stored, it also stores a copy that can be accessed by the administrator.
As shown in Figure 15.9, encryption with EFS requires the presence of at least two certificates in the certificate store on the local computer: one for the user (file owner) and one for a recovery agent account.
You can disable this feature by setting another of your accounts as the recovery agent, but in a domain, normally your domain administrator will set this policy and not allow you to disable it. So, the administrator can still access your files.
As long as an attacker doesn't gain the password for the recovery agent's account (or yours), your data should still be safe from an attacker, assuming the attacker isn't the same person as the recovery agent.
It's important to have strong passwords, keep them safe, and avoid running malicious software that could access the data directly.
Thanks for your views on my YouTube video. I am certainly no expert on the details of current encryption technology and so my answer won't do your question justice. The video is intended to give someone who is unfamiliar with the details of EFS a more coherent understanding of how it all works.
However, having said that.. it looks like the previous reply answers the question. Hashes are not reversible. I think I used the words 'virtually impossible' to reverse engineer.. but really Hashes are used because they cannot be reversed to give the passwords. Password crack programs, from my limited understanding, start with a plaintext word from a dictionary, use the same hash algorithm and attempt to generate the same hash as the target hash they are attempting to decrypt. As long as you've used a good password, you can't crack the hash. Bad passwords are the only way passwords get cracked.
It is easy to set up an administrative account if you have access to any machine, but any new account set up will not have access to any private keys. A recovery agent has to be set up PRIOR to encrypting anything with EFS in order for the recovery agent to have access to a user's file. But then, both the Recovery Agents private key hash and the target person's private key hash are both unrecoverable to a new admin account.
I think that's the way it needs to work, or there is no real security.
Dave Crabbe
If I built an application that accessed some of the data from say Gmail, Twitter and Facebook, and I want the user to be able to only have to enter their authentication info once, and it's reset after some days or weeks, what is the best way to do this, dynamically, in Ruby?
I see a lot of people just having a config file of their clients'/users' credentials like so:
gmail_account:
username: myClient
password: myClientsPassword
This seems a) like it's very insecure, and b) it wouldn't work if I wanted to store this kind of information for thousands of users. What is the recommended way to do this?
I would like to be able to build an interface on top of these services, so having to enter credentials every time the user made a transaction isn't feasible.
If you're comforatable with the potential liability when a hacker gets into your database / filesystem, then go for it. And in all fairness, you should also disclose to your users that their passwords will be stored on your system, and let them decide if they want to give your program that level of trust.
But why do this in the first place? Facebook Connect and Twitter & Google using OAuth there's no need for you to store user passwords at all. At some point a user's cookies will expire (or they'll try to access your site from another computer) and they'll have to re-authenticate. You can't prevent re-authentication - instead, you should make it as easy for the end user to handle as possible.
Such services are providing OpenAuth authorization. You are strongly recommended to have a look at it.
Security
I assume your application needs to know the password in plaintext. Then there is no way around storing it in some kind of plain way.
Store in some kind of encoded way eg. Base64, this protects you from knowing password when looking through the database with your eyes, but it does not protect you from anything else.
Ensure that the files are not readable from any other user
Encrypt your harddrive, so nobody can get the passwords from stealing your harddrive. Your computer will require inputung you the password during booting.
Storing
There is nothing wrong with storing much data in your filesystem. For better performance you can do the following
One file for each user, so the filesystem and not ruby needs to search for the data
Make a lot of subdirectorys. Some filessystems performance suffer's if you put to many files into one directory. eg. put the file 'abcd' into 'a/b/c/d'
You could use a database instead of the filesystem
This is the way it works for instance for fetcmailrc which has to be chmod to 600 (readeable and writable only by his owner). And yes, it contains the plain password.
I would strongly suggest you to use OAuth, but if you have to store the passwords (please be absolutely sure that you need to do it) you could use the OpenSSL library to encrypt the passwords. The OpenSSL library is quite poorly documented in Ruby, but as far as I know they are quite similar to the C OpenSSL library. Since I think you should use OAuth, and not storing the passwords I'll let you find the documentation yourself.
However, for the OAuth approach, you want to take a look at the OAuth gem. Google, Twitter (which I recommend you to use the excellent twitter gem for) and facebook (which has two seemingly good alternatives: RFacebook and facebooker)
I was thinking of making a small tool. It is not important what the tool will do. The important thing, is that the tool will need to store some sensitive information on the user's HDD. EDIT: The information that will be stored is USER'S information - I'm not trying to protect my own content, that I distribute with the app.
I understand that I need to encrypt this information. But then, where do I safely store the encryption password? It's some sort of an infinite recursion...
So, is there a way, to encrypt information on windows, and have windows securely manage the passwords? When I say windows I mean Windows XP SP2 or later.
I should also note, that users on the same system must not have access to other users information (even when they are both running my application).
I'm looking for both - .NET 2.0 (C#) and native (C/C++) solutions to this problem.
is there a way, to encrypt information on windows, and have windows securely manage the passwords?
CryptProtectData: http://msdn.microsoft.com/en-us/library/windows/desktop/aa380261(v=vs.85).aspx
Using from .NET: http://msdn.microsoft.com/en-us/library/aa302402.aspx
Historically, Protected Storage (available in XP, read-only in vista+): http://msdn.microsoft.com/en-us/library/bb432403%28VS.85%29.aspx
You should consider using DPAPI for this purpose. It will encrypt your data with a special (internal) symmetric key which is on per-user basis. You don't even need to ask for passwords in this case, because different users on the system will have different keys assigned to them.
The downside of it might be that you can't recover the data if the user is deleted/Windows reinstalled (I believe that this is the case, not quite sure though). In that case encrypt the data with a "self-generated" key derived from the password and store the password in registry/file encrypted using DPAPI.
You can use the native encryption facility. Set the encrypt attribute on your folder or file (from the property page, click on the "advanced" button). Then you can set the users that can access the file (by default this only includes the file creator). The big advantage of this solution is that it is totally transparent from the application and the users points of view.
To do it programmatically: using the Win32 API, call EncryptFile() on the directory where you want to store your sensitive per-user data. From now on all newly created files within this dir will be encrypted and only readable by their creator (that would be the current user of your app). Alternatively you can use the FILE_ATTRIBUTE_ENCRYPTED flag on individual files at creation time. You can check encryption info from the explorer on the file's property page, and see that app-created files are correctly encrypted and restricted to their respective users. There is no password to store or use, everything is transparent.
If you want to hide data from all users then you can create a special app-specific user and impersonate it from your app. This, along with ACLs, is the blessed technique on Windows for system services.
You might want to look at Isolated Storage, which is a way of storing settings and other data on a per-application data automatically.
See an example and MSDN.
This is an alternative to storing normal settings in the registry, a better one in a lot of cases... I'm not sure how the data is stored to file however so you'd need to check, you wouldn't want it to be accessible, even encrypted, to other users. From memory only the app. that created the storage can open it - but that needs checking.
Edit:
From memory when I last used this, a good approach is to write a "Setting" class which handles all the settings etc. in your app. This class then has the equivalent of Serialize and DeSerialize methods which allow it to write all its data to an IsolatedStorage file, or load them back again.
The extra advantage of implementing it in this way is you can use attributes to mark up bits of the source and can then use a Property Grid to quickly give you user-edit control of settings (the Property Grid manipulates class properties at runtime using reflection).
I recommend you look at the Enterprise Library Cryptography Application Block. Check this blog post. Windows has a built in Data Protection API for encrypting data, but the Crypto Application Block makes it more straightforward.
Um, what you're trying to achieve is exactly what DRM tried to achieve. Encrypt something then give the user the keys (however obfuscated) and the crypto. They did it with DVDs. They did it with Blu-Ray. They did it with iTunes.
What you are proposing to do will never be secure. Your average lay person will probably not figure it out, but any sufficiently motivated attacker will work it out and discover the keys, the algorithm and decrypt the data.
If all you're doing is encrypting user data then ask the user for their password. If you're trying to protect your internal data from the user running the application you're S.O.L.
Erm hash the password? You don't need to store the real deal anywhere on the machine just a hashed password (possibly salted too). Then when the user enters their password you perform the same operation on that and compare it to the hashed one you've stored on disk.
Is it possible to store passwords on the local system (Windows XP) that can only be accessed by the application itself?
My instinctive answer would be "no". Even if some kind of hashing or encyption is used I would think that as long as the source code is available then the determined seeker could always use this to retrieve the password.
I'm working on a personal open source hobby project in which I would like to give users the option of storing passwords on disk so that they don't need to type them every time they use the software. One example of a password that could be stored would be the one used to authenticate on their network's proxy server.
There are a few related questions here on Stack Overflow and the most appropriate solution sounds like using an operating system service like DPAPI.
Is the basic premise correct that as long as the password is retrievable by the software without any user input, and the source code is open source, that the password will always be retrievable by a (suitably technically and willfully inclined) passer-by?
You could read about the Pidgin developers' take on it here:Plain Text Passwords.
Using the DPAPI in UserData mode will only allow your account on your machine to access the encrypted data.
It generates a master key based off of your login credentials and uses that for the encryption.
If the password is retrievable by the software without any user input, then the password will always be retrievable by a (suitably technically and willfully inclined) passer-by. Open or closed source only affects how much effort is involved.
Absolutely, you can write a program to store passwords securely.
Using AES, you could have your program generate an AES Key, and have that key stored in an operating system protected area. In WinXP, this is the registry, encrypted with DPAPI. Thus the only way to access the key is to have physical access to the machine.
You need to ensure that when you generate your AES key that you do so in a cryptographically secure manner. Just using RAND won't work, nor will generating a random character string.
Open Source has very little to do with security (in my opinion). Given the level of sophistication in tools for reverse engineering source code, even if you had a closed source solution, people determined to snoop at your code could do so.
Your effort is better spent ensuring that you follow best practice guidelines while using the chosen encryption scheme. I would argue that having your code openly looked at by a larger community would actually make your code more secure; vulnerabilities and threats would likely be identified sooner with a larger audience looking through your code.