[discrete]
[[hashing-settings]]
==== User cache and password hash algorithms

Certain realms store user credentials in memory. To limit exposure
to credential theft and mitigate credential compromise, the cache only stores
a hashed version of the user credentials in memory. By default, the user cache
is hashed with a salted `sha-256` hash algorithm. You can use a different
hashing algorithm by setting the `cache.hash_algo` realm settings to any of the
following values:

[[cache-hash-algo]]
.Cache hash algorithms
|=======================
| Algorithm           | | | Description
| `ssha256`           | | | Uses a salted `sha-256` algorithm (default).
| `md5`               | | | Uses `MD5` algorithm.
| `sha1`              | | | Uses `SHA1` algorithm.
| `bcrypt`            | | | Uses `bcrypt` algorithm with salt generated in 1024 rounds.
| `bcrypt4`           | | | Uses `bcrypt` algorithm with salt generated in 16 rounds.
| `bcrypt5`           | | | Uses `bcrypt` algorithm with salt generated in 32 rounds.
| `bcrypt6`           | | | Uses `bcrypt` algorithm with salt generated in 64 rounds.
| `bcrypt7`           | | | Uses `bcrypt` algorithm with salt generated in 128 rounds.
| `bcrypt8`           | | | Uses `bcrypt` algorithm with salt generated in 256 rounds.
| `bcrypt9`           | | | Uses `bcrypt` algorithm with salt generated in 512 rounds.
| `pbkdf2`            | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 10000 iterations.
| `pbkdf2_1000`       | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 1000 iterations.
| `pbkdf2_10000`      | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 10000 iterations.
| `pbkdf2_50000`      | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 50000 iterations.
| `pbkdf2_100000`     | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 100000 iterations.
| `pbkdf2_500000`     | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                              pseudorandom function using 500000 iterations.
| `pbkdf2_1000000`    | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 1000000 iterations.
| `noop`,`clear_text` | | | Doesn't hash the credentials and keeps it in clear text in
                            memory. CAUTION: keeping clear text is considered insecure
                            and can be compromised at the OS level (for example through
                            memory dumps and using `ptrace`).
|=======================

Likewise, realms that store passwords hash them using cryptographically strong 
and password-specific salt values. You can configure the algorithm for password 
hashing by setting the `xpack.security.authc.password_hashing.algorithm` setting 
to one of the following:

[[password-hashing-algorithms]]
.Password hashing algorithms
|=======================
| Algorithm           | | | Description

| `bcrypt`            | | | Uses `bcrypt` algorithm with salt generated in 1024 rounds. (default)
| `bcrypt4`           | | | Uses `bcrypt` algorithm with salt generated in 16 rounds.
| `bcrypt5`           | | | Uses `bcrypt` algorithm with salt generated in 32 rounds.
| `bcrypt6`           | | | Uses `bcrypt` algorithm with salt generated in 64 rounds.
| `bcrypt7`           | | | Uses `bcrypt` algorithm with salt generated in 128 rounds.
| `bcrypt8`           | | | Uses `bcrypt` algorithm with salt generated in 256 rounds.
| `bcrypt9`           | | | Uses `bcrypt` algorithm with salt generated in 512 rounds.
| `bcrypt10`          | | | Uses `bcrypt` algorithm with salt generated in 1024 rounds.
| `bcrypt11`          | | | Uses `bcrypt` algorithm with salt generated in 2048 rounds.
| `bcrypt12`          | | | Uses `bcrypt` algorithm with salt generated in 4096 rounds.
| `bcrypt13`          | | | Uses `bcrypt` algorithm with salt generated in 8192 rounds.
| `bcrypt14`          | | | Uses `bcrypt` algorithm with salt generated in 16384 rounds.
| `pbkdf2`            | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 10000 iterations.
| `pbkdf2_1000`       | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 1000 iterations.
| `pbkdf2_10000`      | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 10000 iterations.
| `pbkdf2_50000`      | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 50000 iterations.
| `pbkdf2_100000`     | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 100000 iterations.
| `pbkdf2_500000`     | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                              pseudorandom function using 500000 iterations.
| `pbkdf2_1000000`    | | | Uses `PBKDF2` key derivation function with `HMAC-SHA512` as a
                             pseudorandom function using 1000000 iterations.
|=======================