I have a question about Core Data encryption. I'm storing some sensitive user data in a Core Data SQLite database. The critical values are all transformables and I'm using AES256 to encrypt and decrypt them 'on the fly', including an individual IV for every value. The encryption key is the SHA512 hash of the password the user has chosen. This works very well so far.
Now about the user password. When the user launches the app he is asked for his password. The password is being hashed with SHA512 and stored in the iOS keychain. For every write or read operation the NSValueTransformer will get the password from the keychain. If the app is being closed, I delete the password hash from the keychain.
In my Core Data database I have a special entity which has a random number != 0 as it's only value. To test if the user has entered the correct password I fetch this entity and read the number. If it is =! 0, I know that the password was correct because when the decryption fails the NSValueTransformer always returns 0.
Now my actual questions: Would you consider this a good approach on encryption? How else would you test if the entered password is correct?
I'm a little concerned that storing the password hash in the keychain while the app is running makes everything slower, because the NSValueTransformer has to access the keychain all the time. Would it be sufficiently secure to just keep the password hash in memory, so it'll be deleted when the app closes?
You shouldn't use the hash of the password, hashes are designed to be fast so it's (comparatively) easy to do a brute-force attack. Use a key derivation function like PBKDF2.
Don't use a key directly derived from the password as an encryption key. If the user changes the password, you need to reencrypt all data and backups become worthless. Use a randomly generated encryption key that you encrypt with a key encryption key based on the password.
I'm not so sure about storing the hash in the keychain instead of just holding it in memory. The last time I looked into this, it was comparetively easy to decrypt the keychain. And every attacker that can read the memory of your running app will most likely be able to snoop on the keychain access or the decrypted data. Just keep it in memory and make sure to wipe the memory if the app suspends into background etc. This holds obviously also true for every piece of decrypted data.
[EDIT: #JeffLockhart to clarify the procedure for a master encryption key]
you generate a random key to encrypt your data, let's call it key A. You could use SecRandomCopyBytes to generate key A, see Apple's CryptoExcercise for a usage example. You use key A to encrypt the user data. To save key A, you have to encrypt key A with a second key B. You shouldn't use the password directly as key B, because of fast brute-force or dictionary attacks. So you derive a key from the password with a PBKDF, like in this
stackoverflow answer. You then encrypt key A with key B, e.g. using CCCrypt. You save the encrypted key A and the salt used to derive key B it.
To decrypt, the user enters the password, you derive key B using the password and the salt. You decrypt key A using the derived key B. Hope that clarifies.
You could have a look at this:
Secure Incremental Store
They have implemented a NSIncrementalStore subclass which is using an encrypted SQLite-Database. This is a drop-in replacement for Apple's SQLite Store. Comes with a price tag as well.
Related
I have heard about Secure Enclave. In which after key generation, data can be encrypted by SecKeyCreateEncryptedData method.
My Use Case: I want to store some sensitive data persistently. For security purposes, I have encrypted data by above method using Secure Enclave.
Now just want to know is it a legal way to store encrypted data in NSUserDefaults or Keychain. or there is something else that should be done.
Any help would be much appreciated!
Since the data is encrypted you can store it anyway you want. Without the key inside the Secure Enclave the data is worthless.
There are several approaches you can go for: save it to UserDefaults, create a JSON inside documents directory etc.
Let's assume you want to save it to UserDefaults then have a look at this link:
How can I use UserDefaults in Swift?
Valuable article about secure enclave and cryptokit:
https://www.andyibanez.com/posts/cryptokit-secure-enclave/
I want to store some keys in an encrypted form in database in a secured fashion. At the same time I need to use the non-encrypted(original) form of the keys somewhere in my code. I planned to use PBKDF2 for password hashing PBKDF2. Is it possible to decrypt the key stored in the database in an encrypted form using PBKDF2. Or Is there any simple and secure procedures available?
Passwords and secret keys are usually stored in their hashed form. That means they are processed through a hash function before being saved to the database. A good hash function such as bcrypt has the following properties:
it produces the same output for the same input
it produces very different output for different inputs
its output is not distinguishable from random
it is not reversible
The last property has a very important security implication: when someone gets access to the database, they cannot recover the original keys because the hash function is not reversible, especially when the hash is salted to prevent attackers from using rainbow tables.
That means if you want to recover the keys later on, you have to save them in encrypted (not hashed) form. An encryption function has similar properties like a hash function, with the key difference that it is in fact reversible. For this decryption step you need a key, which needs to be stored somewhere.
You could store the the key in your application config but that would mean that if someone gains access to your server, they would be able to retrieve the encryption key and decrypt all the stored keys.
I suggest an alternative approach, which will users allow to retrieve only their own stored keys. It is based on the idea that the keys are encrypted with a user-specific password that only the user knows. Whenever you need to perform an action that needs to store or retrieve the keys, the user is prompted for their password. This way, neither yourself nor an attacker will be able to retrieve them, but your program can access them if the user allows it by entering his password.
Store a conventionally hashed user password in the database e.g. using bcrypt
Allow users to store additional password with the following procedure:
Prompt for user password and keys to store
Hash password and compare with database to authenticate
Generate salt for each entered key
Use user-entered password and salt to encrypt keys to store e.g. with AES encryption
Store salt and encrypted keys in database
To retrieve the stored keys in an action requiring them in plain text form:
Prompt for user password
Hash password and compare with database to authenticate
Retrieve encrypted keys and salt from the database
Decrypt stored keys using user password and salt
Be careful to remove user submitted passwords from the application log ;-)
Passwords are never stored in a database in any way that people can decrypt them afterwards. There is no guarantee that someone will not hack your database tables and steal everything that you have stored.
If you store an encrypted (hashed) password for each user, even if your database is hacked, it will take those who stole your decrypted passwords a LOT of time to find out the actual passwords. They can always use your same encryption and compare the resulting hash of common passwords. For example, they can encrypt "MyPassword123" and then compare that hashed password to every password in your database. Weak passwords can still be guessed using this pattern.
Therefore, even non-decryptable passwords have their weaknesses, but if you allow someone to decrypt what you store, then basically it's extremely easy for them to get every single one of your user's passwords. Very bad practice. Some of the biggest and most "secure" companies have had their stored Password Hashes stolen, so you cannot assume you will not be a victim.
I had encountered this same problem with bcrypt using Ruby where it works for user validation since it compares the difference between a user entered clear text and the hashed password and the hashed password never decrypts to clear text. One of the gems I have found that may solve your problem is encryptor, which encrypts using several different keys. So what you can do is to keep your password in the database, while keeping the keys securely in another location (a file in storage).
More information can be found in the rubygems page.
More recent answers to this question:
If you're on Rails <7, use Lockbox
If you're on Rails >=7, encryption is now built in to ActiveRecord
How does it work, that devise knows salts for encrypted passwords? Where does it store these hashes and how is that safe?
This is one of the main files for creating passwords: Devise::DatabaseAuthenticatable
Salt is not stored in the database, it is a string generated by this C program that is run by the BCrypt::Engine.generate_salt() function __bc_salt:
prefix = "$2a$05$CCCCCCCCCCCCCCCCCCCCC.E5YPO9kmyuRGyh0XouQYb4YMJKvyOeW"
__bc_salt(prefix, cost, OpenSSL::Random.random_bytes(MAX_SALT_LENGTH))
This can be found here:
BCrypt::Engine
With some other interesting code here: BCrypt::Password
From what I can gather though, the salt itself is the 29 characters that appear after the third $ in the encrypted password. This alone cannot tell you the password though, since you also need to know the pepper which is based on your apps secret key (usually stored in your /config/initializers/secret_token.rb)
Conclusion: In order to decrypt a password, one would have to be using the right version of BCrypt, have obtained the secret token from the app, and have the encrypted password, and I think that at that point, user passwords are probably the least of your security concerns, so I think its pretty safe.
I'm building an application with Rails and will be pulling timesheets from Harvest, a timetracking app. I'm using an API wrapper called harvested. To be able to interface with their API, I need to provide a subdomain, username and password.
Right now, I'm just storing the passwords as plain strings and have not done any encryption. Would like to encrypt them before storing in the DB. If I encrypt the passwords before storing, can I still use the encrypted password for authenticating with the Harvester API?
OAuth exists for this very reason. Storing plaintext is obviously a bad idea, but storing something encrypted that you then decrypt is ALSO a bad idea.
Modern password flows use one-way encryption: encrypting the password and then comparing it an already encrypted value in the database. This allows use of algorithms that can encrypt easily but are essentially impossible to decrypt. Using an algorithm that allows your application to easily decrypt database fields will also allow an attacker to do the same.
With a one-way flow (encryption only), even if a user gets ahold of your encrypted passwords, they are unusable since anything entered in the password box will be passed through the encryption again before testing for validity.
TL;DR
Use OAuth as someone else pointed out: https://github.com/harvesthq/api/blob/master/Authentication/OAuth%202.0.md
I'm trying to figure out a way to store user-generated text securely in a database (so that only the user is the one who can access his/her stored text). I could have Rails encrypt and decrypt the user's text entries using the user's password as the key, but if the user ever forgot their password there would be no way to ever decrypt their previous content/text (since the Rails app uses BCrypt to store only a hash of the password).
Does anyone know how that could be done? It looks like Dropbox does something like it: "All files stored on Dropbox servers are encrypted (AES-256) and are inaccessible without your account password." (http://www.dropbox.com/help/27) Yet they allow you to reset your password and I'm assuming they don't store your plain text password anywhere.
What am I missing? Any suggestions would be greatly appreciated. Thanks!
Logic dictates that are only two options:
You encrypt using a key known to the server (user's key hash or some other identifier). Intruders can potentially read all the encrypted data, but the user can never lose the encryption token because it is on your server.
You encrypt the data using a key known to the user only (e.g. his password). Then intruders will not be able to read encrypted data, but if the user loses his key, the data is as good as a pile of random bits.
It's clear that Dropbox has chosen (1) from the fact that they allow to reset your password.
Build on Gintautas' Option 1 with a two-prong encryption plan:
Apply option 1, with a key that is known to the server, and
Store the database on disk in an encrypted format with a key that is known only to the server. E.g., in an encrypted volume. When the server starts up, the key must be manually entered in order to access the database.
This "static security" provided by part 2 protects against an intruder in the system gaining access to the database files. Maybe not 100% the exact security you're after, but getting closer.