(PHP 7 >= 7.2.0, PHP 8)
sodium_crypto_kx_secretkey — Extract the secret key from a crypto_kx keypair.
$key_pair
) : stringExtract the secret key from a crypto_kx keypair.
key_pairX25519 keypair, such as one generated by sodium_crypto_kx_keypair().
X25519 secret key.