In this post I'll look at some of the source code that makes up the ASP.NET Core Identity framework. In particular, I'm going to look at the PasswordHasher<T> implementation, and how it handles hashing user passwords for verification and storage. You'll also see how it handles updating the hashing algorithm used by your app, while maintaining backwards compatibility with existing hash functions.
I'll start by describing where password hashing fits into ASP.NET Core Identity overall, and the functionality provided by the IPasswordHasher<TUser> interface. Then I'll provide a high-level overview of the PasswordHasher<T> implementation, before finally digging into a few details.
In the next post, I'll show how to create a custom IPasswordHasher<TUser> implementation, so you can integrate an existing user database into ASP.NET Core Identity. This will let you use your existing password hashes without having to reset every user's password, and optionally allow you to migrate them to the suggested ASP.NET Core Identity hash format.
ASP.NET Core Identity and password hashing
You're no doubt familiar with the "username and password" authentication flow used by the vast majority of web apps. ASP.NET Core Identity uses this flow by default (I'm going to ignore third-party login providers for the purposes of this article).
When a user registers with the app, they provide a username and password (and any other required information). The app will create a hash of the password, and store it in the database along with the user's details.
A hash is a one way function, so given the password you can work out the hash, but given the hash you can't get the original password back. For security reasons, the characteristics of the hash function are important; in particular, the hash function should be relatively costly to compute, so that if your database of password hashes were to be compromised, it would take a long time to crack them.
Important You should never store a user's password directly in a database (or anywhere else). Also, you should never store the password in an encrypted format, in which you can recover the password. Instead, passwords should only ever be stored as a hash of the original, using a strong cryptographic hash function designed for this purpose.
When it comes to logging in, users POST their username and password to the app. The app will take the identifier and attempt to find an existing account in its database. If it finds the account, it retrieves the stored password hash associated with the account.
The app then hashes the password that was submitted, and compares the two hashes. If the hashes match, then the password is correct, and the user can be authenticated. If the hashes don't match, the user provided the wrong password, and should be rejected.
The IPasswordHasher<TUser> interface
With this typical flow, there are two different scenarios in which we need to hash a password:
- When the user registers - to create the password hash that will be stored in the database
- When the user logs in - to hash the provided password and compare it to the stored hash
These two scenarios are closely related, and are encapsulated in the IPasswordHasher<TUser> interface in ASP.NET Core Identity. The Identity framework is designed to be highly extensible, so most of the key parts of infrastructure are exposed as interfaces, with default implementations that are registered by default.
The IPasswordHasher<TUser> is one such component. It's used in the two scenarios described above and exposes a method for each, as shown below.
Note: In this post I'm going to show the source code as it exists in the ASP.NET Core 2.0 release, by using the rel/2.0.0 tag in the Identity Github repo. You can view the full source for the IPasswordHasher<TUser> here.
public interface IPasswordHasher<TUser> where TUser : class{ string HashPassword(TUser user, string password); PasswordVerificationResult VerifyHashedPassword( TUser user, string hashedPassword, string providedPassword);}
The IPasswordHasher<TUser> interface is a generic interface, where the generic parameter is the type representing a User in the system - often a class deriving from IdentityUser.
When a new user registers, the Identity framework calls HashPashword() to hash the provided password, before storing it in the database. When a user logs in, the framework calls VerifyHashedPassword() with the user account, the stored password hash, and the password provided by the user.
Pretty self explanatory right? Let's take a look at the default implementation of this interface.
The default PasswordHasher<TUser> implementation
The default implementation in the Identity framework is the PasswordHasher<TUser> class (source code). This clas is designed to work with two different hashing formats:
- ASP.NET Identity Version 2: PBKDF2 with HMAC-SHA1, 128-bit salt, 256-bit subkey, 1000 iterations
- ASP.NET Core Identity Version 3: PBKDF2 with HMAC-SHA256, 128-bit salt, 256-bit subkey, 10000 iterations
The PasswordHasher<TUser> class can hash passwords in both of these formats, as well as verify passwords stored in either one.
Verifying hashed passwords
When a password is provided that you need to compare against a hashed version, the PasswordHasher<TUser> needs to know which format was used to hash the password. To do this, it preppends a single byte to the hash before storing it in the database (Base64 encoded).
When a password needs to be verified, the hasher checks the first byte, and uses the appropriate algorithm to hash the provided password.
public virtual PasswordVerificationResult VerifyHashedPassword(TUser user, string hashedPassword, string providedPassword){ // Convert the stored Base64 password to bytes byte[] decodedHashedPassword = Convert.FromBase64String(hashedPassword); // The first byte indicates the format of the stored hash switch (decodedHashedPassword[0]) { case 0x00: if (VerifyHashedPasswordV2(decodedHashedPassword, providedPassword)) { // This is an old password hash format - the caller needs to rehash if we're not running in an older compat mode. return (_compatibilityMode == PasswordHasherCompatibilityMode.IdentityV3) ? PasswordVerificationResult.SuccessRehashNeeded : PasswordVerificationResult.Success; } else { return PasswordVerificationResult.Failed; } case 0x01: if (VerifyHashedPasswordV3(decodedHashedPassword, providedPassword)) { return PasswordVerificationResult.Success; } else { return PasswordVerificationResult.Failed; } default: return PasswordVerificationResult.Failed; // unknown format marker }}
When the password is verified, the hasher returns one of three results:
PasswordVerificationResult.Failed - the provided password was incorrectPasswordVerificationResult.Success - the provided password was correctPasswordVerificationResult.SuccessRehashNeeded - the provided password was correct, but the stored hash should be updated
The switch statement in VerifyHashedPassword() has two main cases - one for Identity v2 hashing, and one for Identity v3 hashing. If the password has been stored using the older v2 hashing algorithm, and the provided password is correct, then the hasher will either return Success or SuccessRehashNeeded.
Which result it chooses is based on the PasswordHasherCompatibilityMode which is passed in via an IOptions<PasswordHasherOptions> object. This lets you choose whether or not to rehash the older passwords; if you need the password hashes to remain compatible with Identity v2, then you might want to keep the older hash format.
As well as verifying hashed passwords, the PasswordHasher<TUser> is used to create new hashes.
Hashing new passwords
The HashPassword() function is called when a new user registers, and the password needs hashing before it's stored in the database. It's also called after an old v2 format password hash is verified, and needs rehashing.
private readonly RandomNumberGenerator _rng;public virtual string HashPassword(TUser user, string password){ if (_compatibilityMode == PasswordHasherCompatibilityMode.IdentityV2) { return Convert.ToBase64String(HashPasswordV2(password, _rng)); } else { return Convert.ToBase64String(HashPasswordV3(password, _rng)); }}
The hashes are generated in the correct format, depending on the PasswordHasherCompatibilityMode set in the options, which is then Base64 encoded before it's stored in the database.
I won't dwell on the hashing algorithms themselves too much, but as an example, the HashPasswordV2 function is shown below. Of particular note is the line 4th from the bottom, where the "first byte" format marker is set to 0x00:
private static byte[] HashPasswordV2(string password, RandomNumberGenerator rng){ const KeyDerivationPrf Pbkdf2Prf = KeyDerivationPrf.HMACSHA1; // default for Rfc2898DeriveBytes const int Pbkdf2IterCount = 1000; // default for Rfc2898DeriveBytes const int Pbkdf2SubkeyLength = 256 / 8; // 256 bits const int SaltSize = 128 / 8; // 128 bits // Produce a version 2 text hash. byte[] salt = new byte[SaltSize]; rng.GetBytes(salt); byte[] subkey = KeyDerivation.Pbkdf2(password, salt, Pbkdf2Prf, Pbkdf2IterCount, Pbkdf2SubkeyLength); var outputBytes = new byte[1 + SaltSize + Pbkdf2SubkeyLength]; outputBytes[0] = 0x00; // format marker Buffer.BlockCopy(salt, 0, outputBytes, 1, SaltSize); Buffer.BlockCopy(subkey, 0, outputBytes, 1 + SaltSize, Pbkdf2SubkeyLength); return outputBytes;}
The "first byte" format marker is the byte that is used by the VerifyHashedPassword() function to identify the format of the stored password. A format marker of 0x00 indicates that the password is stored in the v2 format; a value of 0x01 indicates the password is stored in the v3 format. In the next post, we'll use this to extend the class and support other formats too.
That's pretty much all there is to the PasswordHasher<TUser> class. If you'd like to see more details of the hashing algorithms themselves, I suggest checking out the source code.
Summary
The IPasswordHasher<TUser> is used by the ASP.NET Core Identity framework to both hash passwords for storage, and to verify that a provided password matches a stored hash. The default implementation PasswordHasher<TUser> supports two different formats of hash function: one used by Identity v2, and a stronger version used by ASP.NET Core Identity v3.
If you need to keep the passwords in the v2 format you can set the PasswordHasherCompatibilityMode on the IOptions<PasswordHasherOptions> object in the constructor to IdentityV2. If you use IdentityV3 instead, new passwords will be hashed with the stronger algorithm, and when old passwords are verified, they will be rehashed with the newer, stronger algorithm.
FAQs
ASP.NET Core Identity and password hashing
The app will create a hash of the password, and store it in the database along with the user's details. A hash is a one way function, so given the password you can work out the hash, but given the hash you can't get the original password back.
What is Aspnetcore identity? ›
ASP.NET Core Identity: Is an API that supports user interface (UI) login functionality. Manages users, passwords, profile data, roles, claims, tokens, email confirmation, and more.
What hashing algorithm does asp net identity use? ›
The default password hasher for ASP.NET Core Identity uses PBKDF2 for password hashing. While PBKDF2 is not the worst choice, there are certainly better password hashing algorithms available to you, such as bcrypt, scrypt, and Argon2.
What is salt in C#? ›
A 'salt' is a random value that we add to the value we are hashing before it is hashed. The purpose of this being that it adds uniqueness to the data compared to other values we hashed using the same algorithm and therefore dramatically increases the effort required to brute force a hashed password.
How do I encrypt and decrypt password in .NET core? ›
Enter your Password and first click on Encrypt button and then after click on Decrypt.
- Example Of First Enter Password = "rraannaammeett"
- EncodePasswordToBase64 function convert your string and give output. ans= "cnJhYW5uYWFtbWVldHQ="
- DecodeFrom64 function convert your strring and give output. ans="rraannaammeett"
Commonly used hashing algorithms include Message Digest (MDx) algorithms, such as MD5, and Secure Hash Algorithms (SHA), such as SHA-1 and the SHA-2 family that includes the widely used SHA-256 algorithm.
What are core identities examples? ›
An individual has (in the brain) a core identity theme (behaviors then becoming understandable as a theme and variations as in music). We summarize this into four core identities: worshiper, learner, family, and missionary.
How to get user identity in ASP.NET Core? ›
You can create a method to get the current user : private Task<ApplicationUser> GetCurrentUserAsync() => _userManager. GetUserAsync(HttpContext. User);
How to create identity in ASP.NET Core? ›
- From Solution Explorer, right-click on the project > Add > New Scaffolded Item.
- From the left pane of the Add Scaffold dialog, select Identity > Add.
- In the Add Identity dialog, select the options you want. ...
- To use your existing data context, select at least one file to override.
There are many different types of hash algorithms such as RipeMD, Tiger, xxhash and more, but the most common type of hashing used for file integrity checks are MD5, SHA-2 and CRC32.
ASP.NET Identity is Microsoft's user management library for ASP.NET. It includes functionality such as password hashing, password validation, user storage, and claims management. It usually also comes with some basic authentication, bringing its own cookies and multi-factor authentication to the party.
What are two most popular hashing algorithms? ›
There are multiple types of hashing algorithms, but the most common are Message Digest 5 (MD5) and Secure Hashing Algorithm (SHA) 1 and 2.
Why do we need to salt password? ›
Password salting is a technique to protect passwords stored in databases by adding a string of 32 or more characters and then hashing them. Salting prevents hackers who breach an enterprise environment from reverse-engineering passwords and stealing them from the database.
Where are password salts stored? ›
Where should salted passwords be stored? In terms of how this works in the IT infrastructure, salts have to be stored in a database along with the user password, as illustrated below. Salts are recommended to be random and unique per login to mitigate attacks using rainbow tables of pre-computed hashes.
How does password hashing work? ›
Hashing turns your password (or any other piece of data) into a short string of letters and/or numbers using an encryption algorithm. If a website is hacked, cyber criminals don't get access to your password. Instead, they just get access to the encrypted “hash” created by your password.
Is it possible to decrypt password from hash? ›
Instead, passwords are “hashed”, or transformed with a one-way function. The result of the transformation, if one is performed correctly, cannot be reversed, and the original password cannot be “decrypted” from the result of a hash function.
What are the four 3 most secured encryption techniques? ›
Best Encryption Algorithms
- AES. The Advanced Encryption Standard (AES) is the trusted standard algorithm used by the United States government, as well as other organizations. ...
- Triple DES. ...
- RSA. ...
- Blowfish. ...
- Twofish. ...
- Rivest-Shamir-Adleman (RSA).
Hash functions are designed to go only one way. If you have a password, you can easily turn it into a hash, but if you have the hash, the only way to get the original password back is by brute force, trying all possible passwords to find one that would generate the hash that you have.
Which algorithm is best for strong passwords? ›
The Easy Algorithm for Better Passwords
- Come up with a word you remember. Longer words are best, and phrases are even better. ...
- Pick a number you can remember, such as the year you graduated high school. ...
- Add a unique element to each password. ...
- Pick a symbol you will remember. ...
- Lastly, decide the order.
The problem is that the hashes still have to be stored, and anything that is stored can be stolen. Hackers could get the password hashes from the server they are stored on in a number of ways. These include through disgruntled employees, SQL injections and a range of other attacks.
Probably the one most commonly used is SHA-256, which the National Institute of Standards and Technology (NIST) recommends using instead of MD5 or SHA-1. The SHA-256 algorithm returns hash value of 256-bits, or 64 hexadecimal digits.
What are the 3 types of identities? ›
Interpersonal identity development is composed of three elements:
- Categorization: Assigning everyone into categories.
- Identification: Associating others with certain groups.
- Comparison: Comparing groups.
Marcia (1966) based his theory of adolescent identity development on Erikson's (1950/1980) theory of psychosocial identity development and identified four identity statuses: identity diffusion, identity foreclosure, identity moratorium, and identity achievement.
What are the 4 standard identities? ›
The standard identities (algebraic), i.e., the standard identities of algebra are as follows:
- (a + b)2 = a2 + b2 + 2ab.
- (a – b)2 = a2 + b2 – 2ab.
- (a + b)3 = a3 + b3 + 3ab(a + b) = a3 + b3 + 3a2b + 3ab. ...
- (a – b)3 = a3 – b3 – 3ab(a – b) = a3 – b3 – 3a2b + 3ab. ...
- (a + b + c)2 = a2 + b2 + c2 + 2ab + 2bc + 2ca.
Difference between auth()->user()->id and Auth::user()->id. Short explanation: No difference really, they both return an instance of Illuminate\Auth\AuthManager . So Auth:: and auth() in your examples will be the exact same object.
How to get user ID in ASP.NET identity? ›
In order to get the Id of the current logged in user using ASP.NET Identity, we use the GetUserId method.
How do I find my core identity? ›
Try these strategies to begin establishing a more concrete, independent identity.
- Define your values. Values and personal beliefs are fundamental aspects of identity. ...
- Make your own choices. ...
- Spend time alone. ...
- Consider how to achieve your ideals.
ASP.NET Core provides many tools and libraries to secure ASP.NET Core apps such as built-in identity providers and third-party identity services such as Facebook, Twitter, and LinkedIn. ASP.NET Core provides several approaches to store app secrets.
How authentication works in .NET Core? ›
Authentication is the process of determining a user's identity. Authorization is the process of determining whether a user has access to a resource. In ASP.NET Core, authentication is handled by the authentication service, IAuthenticationService, which is used by authentication middleware.
How to create asp net identity tables inside existing database? ›
In this article
- Get started with ASP.NET Identity.
- Add Identity packages to your app.
- Add a web form to register users.
- Verify the LocalDb Identity database and tables generated by Entity Framework.
- Configure the application for OWIN authentication.
- Install authentication packages to your application.
Common attacks like brute force attacks can take years or even decades to crack the hash digest, so SHA-2 is considered the most secure hash algorithm.
How to use ASP.NET identity in Web API? ›
You need following simple step for how to use “Identity“. Create a new Project select Asp.net web application. Select Web API and change Authentication with (select Individual User Accounts). Now, your web API project is ready.
How does .NET identity work? ›
ASP.NET Core Identity is a membership system which allows you to add login functionality to your application. Users can create an account and login with a user name and password or they can use an external login providers such as Facebook, Google, Microsoft Account, Twitter and more.
Does ASP.NET identity use cookies? ›
You do not need a separate CookieAuthentication middleware when you are using ASPNET identity. UseIdentity() will do that for you and generate a cookie. You can set the "cookie options" in the AddIdentity block of the application like so: services.
What are the 3 types of hashing? ›
This article focuses on discussing different hash functions: Division Method. Mid Square Method. Folding Method.
Which hash algorithm is fastest? ›
xxHash is an Extremely fast Hash algorithm, running at RAM speed limits. It successfully completes the SMHasher test suite which evaluates collision, dispersion and randomness qualities of hash functions.
What are 4 characteristics a strong hashing algorithm should possess? ›
The Characteristics of Cryptographic Hash Functions
It accepts a message of any length. It produces a fixed-length message digest. It is easy (and therefore fast) to compute the message digest for any given message. The hash is irreversible – it is not possible to generate a message from its message digest.
What is difference between encryption and hashing? ›
Since encryption is two-way, the data can be decrypted so it is readable again. Hashing, on the other hand, is one-way, meaning the plaintext is scrambled into a unique digest, through the use of a salt, that cannot be decrypted.
Can you crack a salted password? ›
As you can see from the above example it is possible to crack passwords that use salts. It just takes much longer and requires more processing time. Hashed passwords that use salts are what most modern authentication systems use.
Is salting passwords different than hashing? ›
Hashing is a one-way process that converts a password to ciphertext using hash algorithms. A hashed password cannot be decrypted, but a hacker can try to reverse engineer it. Password salting adds random characters before or after a password prior to hashing to obfuscate the actual password.
Hashing vs Encryption
However, in almost all circ*mstances, passwords should be hashed, NOT encrypted. Hashing is a one-way function (i.e., it is impossible to "decrypt" a hash and obtain the original plaintext value). Hashing is appropriate for password validation.
Should password salt be secret? ›
It is standard practice not to keep the salt secret but to save it with the password hashed verifier. If the salt is not secret a brute force search is possible if the password is weak such as being on a list of frequent passwords.
Where are password hashes stored? ›
This hash value can be stored on the server instead of the plaintext password. The plaintext is then only used in memory during the login process.
What is the best password hash? ›
To protect passwords, experts suggest using a strong and slow hashing algorithm like Argon2 or Bcrypt, combined with salt (or even better, with salt and pepper). (Basically, avoid faster algorithms for this usage.) To verify file signatures and certificates, SHA-256 is among your best hashing algorithm choices.
What is password hashing with example? ›
Password hashing is defined as putting a password through a hashing algorithm (bcrypt, SHA, etc) to turn plaintext into an unintelligible series of numbers and letters.
Why would an attacker want password hashes? ›
By laterally moving between devices and accounts, attackers can use pass the hash to gain the right credentials to eventually escalate their domain privileges and access more influential systems, such as an administrator account on the domain controller.
How does ASP NET identity work? ›
ASP.NET Identity is Microsoft's user management library for ASP.NET. It includes functionality such as password hashing, password validation, user storage, and claims management. It usually also comes with some basic authentication, bringing its own cookies and multi-factor authentication to the party.
How does hashing work with passwords? ›
Hashing turns your password (or any other piece of data) into a short string of letters and/or numbers using an encryption algorithm. If a website is hacked, cyber criminals don't get access to your password. Instead, they just get access to the encrypted “hash” created by your password.
How does a system authenticate a user when passwords are stored as hash values? ›
How hashing is used in authentication. In authentication systems, when users create a new account and input their chosen password, the application code passes that password through a hashing function and stores the result in the database.
How does ASP Net authentication work? ›
Authentication is the process of determining a user's identity. Authorization is the process of determining whether a user has access to a resource. In ASP.NET Core, authentication is handled by the authentication service, IAuthenticationService, which is used by authentication middleware.
Digital identity verification methods such as biometric verification, face recognition and digital ID document verification can help companies, governments, and financial institutions verify the identity of a person online.
Is password hashing enough? ›
Unfortunately, hashing a password is not nearly enough. It does not take very much computational power to generate a table of hashes of combinations of letters, numbers and symbols. Once you have this store of hashes, you can then compare the hash you want to crack and see if it matches.
Can hashed passwords be hacked? ›
Hacking a hashed password
Hashed passwords are a great way to fight off potential hackers, but it doesn't make it impossible for them to gain access. If a system uses a properly designed algorithm to create a hashed password, chances of hacking are extremely low.
Which are the 3 security requirements that a secure hash functions should satisfy? ›
Data Encryption
A cryptographic hash function must satisfy three criteria: Preimage resistance. Second preimage resistance (weak collision resistance) Strong collision resistance.
Can hashed passwords be decrypted? ›
Instead, passwords are “hashed”, or transformed with a one-way function. The result of the transformation, if one is performed correctly, cannot be reversed, and the original password cannot be “decrypted” from the result of a hash function.
What are the three 3 main types of authentication techniques? ›
There are three basic types of authentication. The first is knowledge-based — something like a password or PIN code that only the identified user would know. The second is property-based, meaning the user possesses an access card, key, key fob or authorized device unique to them. The third is biologically based.
