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Password Storage

Spring Security’s PasswordEncoder interface is used to perform a one-way transformation of a password to let the password be stored securely. Given PasswordEncoder is a one-way transformation, it is not useful when the password transformation needs to be two-way (such as storing credentials used to authenticate to a database). Typically, PasswordEncoder is used for storing a password that needs to be compared to a user-provided password at the time of authentication.

Password Storage History

Throughout the years, the standard mechanism for storing passwords has evolved. In the beginning, passwords were stored in plaintext. The passwords were assumed to be safe because the data store the passwords were saved in required credentials to access it. However, malicious users were able to find ways to get large “data dumps” of usernames and passwords by using attacks such as SQL Injection. As more and more user credentials became public, security experts realized that we needed to do more to protect users' passwords.

Developers were then encouraged to store passwords after running them through a one way hash, such as SHA-256. When a user tried to authenticate, the hashed password would be compared to the hash of the password that they typed. This meant that the system only needed to store the one-way hash of the password. If a breach occurred, only the one-way hashes of the passwords were exposed. Since the hashes were one-way and it was computationally difficult to guess the passwords given the hash, it would not be worth the effort to figure out each password in the system. To defeat this new system, malicious users decided to create lookup tables known as Rainbow Tables. Rather than doing the work of guessing each password every time, they computed the password once and stored it in a lookup table.

To mitigate the effectiveness of Rainbow Tables, developers were encouraged to use salted passwords. Instead of using just the password as input to the hash function, random bytes (known as salt) would be generated for every user’s password. The salt and the user’s password would be run through the hash function to produce a unique hash. The salt would be stored alongside the user’s password in clear text. Then when a user tried to authenticate, the hashed password would be compared to the hash of the stored salt and the password that they typed. The unique salt meant that Rainbow Tables were no longer effective because the hash was different for every salt and password combination.

In modern times, we realize that cryptographic hashes (like SHA-256) are no longer secure. The reason is that with modern hardware we can perform billions of hash calculations a second. This means that we can crack each password individually with ease.

Developers are now encouraged to leverage adaptive one-way functions to store a password. Validation of passwords with adaptive one-way functions are intentionally resource-intensive (they intentionally use a lot of CPU, memory, or other resources). An adaptive one-way function allows configuring a “work factor” that can grow as hardware gets better. We recommend that the “work factor” be tuned to take about one second to verify a password on your system. This trade off is to make it difficult for attackers to crack the password, but not so costly that it puts excessive burden on your own system or irritates users. Spring Security has attempted to provide a good starting point for the “work factor”, but we encourage users to customize the “work factor” for their own system, since the performance varies drastically from system to system. Examples of adaptive one-way functions that should be used include bcrypt, PBKDF2, scrypt, and argon2.

Because adaptive one-way functions are intentionally resource intensive, validating a username and password for every request can significantly degrade the performance of an application. There is nothing Spring Security (or any other library) can do to speed up the validation of the password, since security is gained by making the validation resource intensive. Users are encouraged to exchange the long term credentials (that is, username and password) for a short term credential (such as a session, and OAuth Token, and so on). The short term credential can be validated quickly without any loss in security.

DelegatingPasswordEncoder

Prior to Spring Security 5.0, the default PasswordEncoder was NoOpPasswordEncoder, which required plain-text passwords. Based on the Password History section, you might expect that the default PasswordEncoder would now be something like BCryptPasswordEncoder. However, this ignores three real world problems:

  • Many applications use old password encodings that cannot easily migrate.

  • The best practice for password storage will change again.

  • As a framework, Spring Security cannot make breaking changes frequently.

Instead Spring Security introduces DelegatingPasswordEncoder, which solves all of the problems by:

  • Ensuring that passwords are encoded by using the current password storage recommendations

  • Allowing for validating passwords in modern and legacy formats

  • Allowing for upgrading the encoding in the future

You can easily construct an instance of DelegatingPasswordEncoder by using PasswordEncoderFactories:

Create Default DelegatingPasswordEncoder

  • Java

  • Kotlin

PasswordEncoder passwordEncoder =
    PasswordEncoderFactories.createDelegatingPasswordEncoder();
val passwordEncoder: PasswordEncoder = PasswordEncoderFactories.createDelegatingPasswordEncoder()

Alternatively, you can create your own custom instance:

Create Custom DelegatingPasswordEncoder

  • Java

  • Kotlin

String idForEncode = "bcrypt";
Map encoders = new HashMap<>();
encoders.put(idForEncode, new BCryptPasswordEncoder());
encoders.put("noop", NoOpPasswordEncoder.getInstance());
encoders.put("pbkdf2", Pbkdf2PasswordEncoder.defaultsForSpringSecurity_v5_5());
encoders.put("pbkdf2@SpringSecurity_v5_8", Pbkdf2PasswordEncoder.defaultsForSpringSecurity_v5_8());
encoders.put("scrypt", SCryptPasswordEncoder.defaultsForSpringSecurity_v4_1());
encoders.put("scrypt@SpringSecurity_v5_8", SCryptPasswordEncoder.defaultsForSpringSecurity_v5_8());
encoders.put("argon2", Argon2PasswordEncoder.defaultsForSpringSecurity_v5_2());
encoders.put("argon2@SpringSecurity_v5_8", Argon2PasswordEncoder.defaultsForSpringSecurity_v5_8());
encoders.put("sha256", new StandardPasswordEncoder());

PasswordEncoder passwordEncoder =
    new DelegatingPasswordEncoder(idForEncode, encoders);
val idForEncode = "bcrypt"
val encoders: MutableMap<String, PasswordEncoder> = mutableMapOf()
encoders[idForEncode] = BCryptPasswordEncoder()
encoders["noop"] = NoOpPasswordEncoder.getInstance()
encoders["pbkdf2"] = Pbkdf2PasswordEncoder.defaultsForSpringSecurity_v5_5()
encoders["pbkdf2@SpringSecurity_v5_8"] = Pbkdf2PasswordEncoder.defaultsForSpringSecurity_v5_8()
encoders["scrypt"] = SCryptPasswordEncoder.defaultsForSpringSecurity_v4_1()
encoders["scrypt@SpringSecurity_v5_8"] = SCryptPasswordEncoder.defaultsForSpringSecurity_v5_8()
encoders["argon2"] = Argon2PasswordEncoder.defaultsForSpringSecurity_v5_2()
encoders["argon2@SpringSecurity_v5_8"] = Argon2PasswordEncoder.defaultsForSpringSecurity_v5_8()
encoders["sha256"] = StandardPasswordEncoder()

val passwordEncoder: PasswordEncoder = DelegatingPasswordEncoder(idForEncode, encoders)

Password Storage Format

The general format for a password is:

DelegatingPasswordEncoder Storage Format
{id}encodedPassword

id is an identifier that is used to look up which PasswordEncoder should be used and encodedPassword is the original encoded password for the selected PasswordEncoder. The id must be at the beginning of the password, start with {, and end with }. If the id cannot be found, the id is set to null. For example, the following might be a list of passwords encoded using different id values. All of the original passwords are password.

DelegatingPasswordEncoder Encoded Passwords Example
{bcrypt}$2a$10$dXJ3SW6G7P50lGmMkkmwe.20cQQubK3.HZWzG3YB1tlRy.fqvM/BG (1)
{noop}password (2)
{pbkdf2}5d923b44a6d129f3ddf3e3c8d29412723dcbde72445e8ef6bf3b508fbf17fa4ed4d6b99ca763d8dc (3)
{scrypt}$e0801$8bWJaSu2IKSn9Z9kM+TPXfOc/9bdYSrN1oD9qfVThWEwdRTnO7re7Ei+fUZRJ68k9lTyuTeUp4of4g24hHnazw==$OAOec05+bXxvuu/1qZ6NUR+xQYvYv7BeL1QxwRpY5Pc=  (4)
{sha256}97cde38028ad898ebc02e690819fa220e88c62e0699403e94fff291cfffaf8410849f27605abcbc0 (5)
1 The first password has a PasswordEncoder id of bcrypt and an encodedPassword value of $2a$10$dXJ3SW6G7P50lGmMkkmwe.20cQQubK3.HZWzG3YB1tlRy.fqvM/BG. When matching, it would delegate to BCryptPasswordEncoder
2 The second password has a PasswordEncoder id of noop and encodedPassword value of password. When matching, it would delegate to NoOpPasswordEncoder
3 The third password has a PasswordEncoder id of pbkdf2 and encodedPassword value of 5d923b44a6d129f3ddf3e3c8d29412723dcbde72445e8ef6bf3b508fbf17fa4ed4d6b99ca763d8dc. When matching, it would delegate to Pbkdf2PasswordEncoder
4 The fourth password has a PasswordEncoder id of scrypt and encodedPassword value of $e0801$8bWJaSu2IKSn9Z9kM+TPXfOc/9bdYSrN1oD9qfVThWEwdRTnO7re7Ei+fUZRJ68k9lTyuTeUp4of4g24hHnazw==$OAOec05+bXxvuu/1qZ6NUR+xQYvYv7BeL1QxwRpY5Pc= When matching, it would delegate to SCryptPasswordEncoder
5 The final password has a PasswordEncoder id of sha256 and encodedPassword value of 97cde38028ad898ebc02e690819fa220e88c62e0699403e94fff291cfffaf8410849f27605abcbc0. When matching, it would delegate to StandardPasswordEncoder

Some users might be concerned that the storage format is provided for a potential hacker. This is not a concern because the storage of the password does not rely on the algorithm being a secret. Additionally, most formats are easy for an attacker to figure out without the prefix. For example, BCrypt passwords often start with $2a$.

Password Encoding

The idForEncode passed into the constructor determines which PasswordEncoder is used for encoding passwords. In the DelegatingPasswordEncoder we constructed earlier, that means that the result of encoding password is delegated to BCryptPasswordEncoder and be prefixed with {bcrypt}. The end result looks like the following example:

DelegatingPasswordEncoder Encode Example
{bcrypt}$2a$10$dXJ3SW6G7P50lGmMkkmwe.20cQQubK3.HZWzG3YB1tlRy.fqvM/BG

Password Matching

Matching is based upon the {id} and the mapping of the id to the PasswordEncoder provided in the constructor. Our example in Password Storage Format provides a working example of how this is done. By default, the result of invoking matches(CharSequence, String) with a password and an id that is not mapped (including a null id) results in an IllegalArgumentException. This behavior can be customized by using DelegatingPasswordEncoder.setDefaultPasswordEncoderForMatches(PasswordEncoder).

By using the id, we can match on any password encoding but encode passwords by using the most modern password encoding. This is important, because unlike encryption, password hashes are designed so that there is no simple way to recover the plaintext. Since there is no way to recover the plaintext, it is difficult to migrate the passwords. While it is simple for users to migrate NoOpPasswordEncoder, we chose to include it by default to make it simple for the getting-started experience.

Getting Started Experience

If you are putting together a demo or a sample, it is a bit cumbersome to take time to hash the passwords of your users. There are convenience mechanisms to make this easier, but this is still not intended for production.

withDefaultPasswordEncoder Example

  • Java

  • Kotlin

UserDetails user = User.withDefaultPasswordEncoder()
  .username("user")
  .password("password")
  .roles("user")
  .build();
System.out.println(user.getPassword());
// {bcrypt}$2a$10$dXJ3SW6G7P50lGmMkkmwe.20cQQubK3.HZWzG3YB1tlRy.fqvM/BG
val user = User.withDefaultPasswordEncoder()
    .username("user")
    .password("password")
    .roles("user")
    .build()
println(user.password)
// {bcrypt}$2a$10$dXJ3SW6G7P50lGmMkkmwe.20cQQubK3.HZWzG3YB1tlRy.fqvM/BG

If you are creating multiple users, you can also reuse the builder:

withDefaultPasswordEncoder Reusing the Builder

  • Java

  • Kotlin

UserBuilder users = User.withDefaultPasswordEncoder();
UserDetails user = users
  .username("user")
  .password("password")
  .roles("USER")
  .build();
UserDetails admin = users
  .username("admin")
  .password("password")
  .roles("USER","ADMIN")
  .build();
val users = User.withDefaultPasswordEncoder()
val user = users
    .username("user")
    .password("password")
    .roles("USER")
    .build()
val admin = users
    .username("admin")
    .password("password")
    .roles("USER", "ADMIN")
    .build()

This does hash the password that is stored, but the passwords are still exposed in memory and in the compiled source code. Therefore, it is still not considered secure for a production environment. For production, you should hash your passwords externally.

Encode with Spring Boot CLI

The easiest way to properly encode your password is to use the Spring Boot CLI.

For example, the following example encodes the password of password for use with DelegatingPasswordEncoder:

Spring Boot CLI encodepassword Example
spring encodepassword password
{bcrypt}$2a$10$X5wFBtLrL/kHcmrOGGTrGufsBX8CJ0WpQpF3pgeuxBB/H73BK1DW6

Troubleshooting

The following error occurs when one of the passwords that are stored has no id, as described in Password Storage Format.

java.lang.IllegalArgumentException: There is no PasswordEncoder mapped for the id "null"
	at org.springframework.security.crypto.password.DelegatingPasswordEncoder$UnmappedIdPasswordEncoder.matches(DelegatingPasswordEncoder.java:233)
	at org.springframework.security.crypto.password.DelegatingPasswordEncoder.matches(DelegatingPasswordEncoder.java:196)

The easiest way to resolve it is to figure out how your passwords are currently being stored and explicitly provide the correct PasswordEncoder.

If you are migrating from Spring Security 4.2.x, you can revert to the previous behavior by exposing a NoOpPasswordEncoder bean.

Alternatively, you can prefix all of your passwords with the correct id and continue to use DelegatingPasswordEncoder. For example, if you are using BCrypt, you would migrate your password from something like:

$2a$10$dXJ3SW6G7P50lGmMkkmwe.20cQQubK3.HZWzG3YB1tlRy.fqvM/BG

to

{bcrypt}$2a$10$dXJ3SW6G7P50lGmMkkmwe.20cQQubK3.HZWzG3YB1tlRy.fqvM/BG

For a complete listing of the mappings, see the Javadoc for PasswordEncoderFactories.

BCryptPasswordEncoder

The BCryptPasswordEncoder implementation uses the widely supported bcrypt algorithm to hash the passwords. To make it more resistant to password cracking, bcrypt is deliberately slow. Like other adaptive one-way functions, it should be tuned to take about 1 second to verify a password on your system. The default implementation of BCryptPasswordEncoder uses strength 10 as mentioned in the Javadoc of BCryptPasswordEncoder. You are encouraged to tune and test the strength parameter on your own system so that it takes roughly 1 second to verify a password.

BCryptPasswordEncoder

  • Java

  • Kotlin

// Create an encoder with strength 16
BCryptPasswordEncoder encoder = new BCryptPasswordEncoder(16);
String result = encoder.encode("myPassword");
assertTrue(encoder.matches("myPassword", result));
// Create an encoder with strength 16
val encoder = BCryptPasswordEncoder(16)
val result: String = encoder.encode("myPassword")
assertTrue(encoder.matches("myPassword", result))

Argon2PasswordEncoder

The Argon2PasswordEncoder implementation uses the Argon2 algorithm to hash the passwords. Argon2 is the winner of the Password Hashing Competition. To defeat password cracking on custom hardware, Argon2 is a deliberately slow algorithm that requires large amounts of memory. Like other adaptive one-way functions, it should be tuned to take about 1 second to verify a password on your system. The current implementation of the Argon2PasswordEncoder requires BouncyCastle.

Argon2PasswordEncoder

  • Java

  • Kotlin

// Create an encoder with all the defaults
Argon2PasswordEncoder encoder = Argon2PasswordEncoder.defaultsForSpringSecurity_v5_8();
String result = encoder.encode("myPassword");
assertTrue(encoder.matches("myPassword", result));
// Create an encoder with all the defaults
val encoder = Argon2PasswordEncoder.defaultsForSpringSecurity_v5_8()
val result: String = encoder.encode("myPassword")
assertTrue(encoder.matches("myPassword", result))

Pbkdf2PasswordEncoder

The Pbkdf2PasswordEncoder implementation uses the PBKDF2 algorithm to hash the passwords. To defeat password cracking PBKDF2 is a deliberately slow algorithm. Like other adaptive one-way functions, it should be tuned to take about 1 second to verify a password on your system. This algorithm is a good choice when FIPS certification is required.

Pbkdf2PasswordEncoder

  • Java

  • Kotlin

// Create an encoder with all the defaults
Pbkdf2PasswordEncoder encoder = Pbkdf2PasswordEncoder.defaultsForSpringSecurity_v5_8();
String result = encoder.encode("myPassword");
assertTrue(encoder.matches("myPassword", result));
// Create an encoder with all the defaults
val encoder = Pbkdf2PasswordEncoder.defaultsForSpringSecurity_v5_8()
val result: String = encoder.encode("myPassword")
assertTrue(encoder.matches("myPassword", result))

SCryptPasswordEncoder

The SCryptPasswordEncoder implementation uses the scrypt algorithm to hash the passwords. To defeat password cracking on custom hardware, scrypt is a deliberately slow algorithm that requires large amounts of memory. Like other adaptive one-way functions, it should be tuned to take about 1 second to verify a password on your system.

SCryptPasswordEncoder

  • Java

  • Kotlin

// Create an encoder with all the defaults
SCryptPasswordEncoder encoder = SCryptPasswordEncoder.defaultsForSpringSecurity_v5_8();
String result = encoder.encode("myPassword");
assertTrue(encoder.matches("myPassword", result));
// Create an encoder with all the defaults
val encoder = SCryptPasswordEncoder.defaultsForSpringSecurity_v5_8()
val result: String = encoder.encode("myPassword")
assertTrue(encoder.matches("myPassword", result))

Other PasswordEncoders

There are a significant number of other PasswordEncoder implementations that exist entirely for backward compatibility. They are all deprecated to indicate that they are no longer considered secure. However, there are no plans to remove them, since it is difficult to migrate existing legacy systems.

Password Storage Configuration

Spring Security uses DelegatingPasswordEncoder by default. However, you can customize this by exposing a PasswordEncoder as a Spring bean.

If you are migrating from Spring Security 4.2.x, you can revert to the previous behavior by exposing a NoOpPasswordEncoder bean.

Reverting to NoOpPasswordEncoder is not considered to be secure. You should instead migrate to using DelegatingPasswordEncoder to support secure password encoding.
NoOpPasswordEncoder

  • Java

  • XML

  • Kotlin

@Bean
public static NoOpPasswordEncoder passwordEncoder() {
    return NoOpPasswordEncoder.getInstance();
}
<b:bean id="passwordEncoder"
        class="org.springframework.security.crypto.password.NoOpPasswordEncoder" factory-method="getInstance"/>
@Bean
fun passwordEncoder(): PasswordEncoder {
    return NoOpPasswordEncoder.getInstance();
}

XML Configuration requires the NoOpPasswordEncoder bean name to be passwordEncoder.

Change Password Configuration

Most applications that allow a user to specify a password also require a feature for updating that password.

A Well-Known URL for Changing Passwords indicates a mechanism by which password managers can discover the password update endpoint for a given application.

You can configure Spring Security to provide this discovery endpoint. For example, if the change password endpoint in your application is /change-password, then you can configure Spring Security like so:

Default Change Password Endpoint

  • Java

  • XML

  • Kotlin

http
    .passwordManagement(Customizer.withDefaults())
<sec:password-management/>
http {
    passwordManagement { }
}

Then, when a password manager navigates to /.well-known/change-password then Spring Security will redirect your endpoint, /change-password.

Or, if your endpoint is something other than /change-password, you can also specify that like so:

Change Password Endpoint

  • Java

  • XML

  • Kotlin

http
    .passwordManagement((management) -> management
        .changePasswordPage("/update-password")
    )
<sec:password-management change-password-page="/update-password"/>
http {
    passwordManagement {
        changePasswordPage = "/update-password"
    }
}

With the above configuration, when a password manager navigates to /.well-known/change-password, then Spring Security will redirect to /update-password.