I found a false positive at Site Kit by Google plugin:
FILE: third-party/phpseclib/phpseclib/phpseclib/Crypt/Common/SymmetricKey.php
FOUND 26 ERRORS AND 0 WARNINGS AFFECTING 20 LINES
1144 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1176 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1179 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1184 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1192 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1201 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1203 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1506 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1533 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1538 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1548 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2055 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2152 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2153 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2157 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2253 | ERROR | The constant "MCRYPT_MODE_ECB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_CBC" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_CFB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_NOFB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_OFB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_STREAM" is deprecated since PHP 7.1 and removed since PHP 7.2
2254 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2255 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2260 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2260 | ERROR | The constant "MCRYPT_MODE_ECB" is deprecated since PHP 7.1 and removed since PHP 7.2
2265 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
I found a false positive at Site Kit by Google plugin:
FILE: third-party/phpseclib/phpseclib/phpseclib/Crypt/Common/SymmetricKey.php
FOUND 26 ERRORS AND 0 WARNINGS AFFECTING 20 LINES
1144 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1176 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1179 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1184 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1192 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1201 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1203 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1506 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1533 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1538 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
1548 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2055 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2152 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2153 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2157 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2253 | ERROR | The constant "MCRYPT_MODE_ECB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_CBC" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_CFB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_NOFB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_OFB" is deprecated since PHP 7.1 and removed since PHP 7.2
2253 | ERROR | The constant "MCRYPT_MODE_STREAM" is deprecated since PHP 7.1 and removed since PHP 7.2
2254 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2255 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2260 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead
2260 | ERROR | The constant "MCRYPT_MODE_ECB" is deprecated since PHP 7.1 and removed since PHP 7.2
2265 | ERROR | Extension 'mcrypt' is deprecated since PHP 7.1 and removed since PHP 7.2; Use openssl (preferred) or pecl/mcrypt once available instead