box_secretkey example

    public static function box($plaintext, $nonce, $keypair)
    {
        return self::secretbox(
            $plaintext,
            $nonce,
            self::box_beforenm(
                self::box_secretkey($keypair),
                self::box_publickey($keypair)
            )
        );
    }

    /** * X25519-XSalsa20-Poly1305 with one ephemeral X25519 keypair. * * @internal Do not use this directly. Use ParagonIE_Sodium_Compat. * * @param string $message * @param string $publicKey * @return string * @throws SodiumException * @throws TypeError */

if (ParagonIE_Sodium_Core_Util::strlen($keypair) !== self::CRYPTO_BOX_KEYPAIRBYTES) {
            throw new SodiumException('Argument 1 must be CRYPTO_BOX_KEYPAIRBYTES long.');
        }

        if (self::useNewSodiumAPI()) {
            return (string) sodium_crypto_box_secretkey($keypair);
        }
        if (self::use_fallback('crypto_box_secretkey')) {
            return (string) call_user_func('\\Sodium\\crypto_box_secretkey', $keypair);
        }
        if (PHP_INT_SIZE === 4) {
            return ParagonIE_Sodium_Crypto32::box_secretkey($keypair);
        }
        return ParagonIE_Sodium_Crypto::box_secretkey($keypair);
    }

    /** * Generate an X25519 keypair from a seed. * * @param string $seed * @return string * @throws SodiumException * @throws TypeError * @psalm-suppress MixedArgument * @psalm-suppress UndefinedFunction */

    public static function box($plaintext, $nonce, $keypair)
    {
        $c = self::secretbox(
            $plaintext,
            $nonce,
            self::box_beforenm(
                self::box_secretkey($keypair),
                self::box_publickey($keypair)
            )
        );
        return $c;
    }

    /** * X25519-XSalsa20-Poly1305 with one ephemeral X25519 keypair. * * @internal Do not use this directly. Use ParagonIE_Sodium_Compat. * * @param string $message * @param string $publicKey * @return string * @throws SodiumException * @throws TypeError */

    protected static function box_encrypt($ifp, $ofp, $mlen, $nonce, $boxKeypair)
    {
        if (PHP_INT_SIZE === 4) {
            return self::secretbox_encrypt(
                $ifp,
                $ofp,
                $mlen,
                $nonce,
                ParagonIE_Sodium_Crypto32::box_beforenm(
                    ParagonIE_Sodium_Crypto32::box_secretkey($boxKeypair),
                    ParagonIE_Sodium_Crypto32::box_publickey($boxKeypair)
                )
            );
        }
        return self::secretbox_encrypt(
            $ifp,
            $ofp,
            $mlen,
            $nonce,
            ParagonIE_Sodium_Crypto::box_beforenm(
                ParagonIE_Sodium_Crypto::box_secretkey($boxKeypair),