# sodium_crypto_box_secretkey

(PHP 7 >= 7.2.0, PHP 8)

sodium_crypto_box_secretkey — Extracts the secret key from a crypto_box keypair

### Descripción

sodium_crypto_box_secretkey(string `$key_pair`): string

Given a keypair, fetch only the secret key.

### Parámetros

`key_pair`

  A keypair, such as one generated by sodium_crypto_box_keypair() or sodium_crypto_box_seed_keypair()

### Valores devueltos

X25519 secret key.