Description:
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Hello,

the PHP openssl extension lacks support to export private keys in PKCS#8[1] format. The function openssl_pkey_export()[2] only supports one export format - the traditional PEM format. This is especially a problem when maintaining keys for applications that accept only the PKCS#8 format as input (like the Dovecot MailCrypt plugin[3])

The only PHP libraries I found with PKCS#8 support are phpseclib[4] and SOP\pkcs8[5]. Unfortunately, both lack support for elliptic curve keys, so they're not an option for me either.

The only option left to me, was to spawn a system call to `openssl pkey` just for the sake of migrating the traditional PEM key to PKCS#8 format.

[1] https://en.wikipedia.org/wiki/PKCS_8
[2] https://secure.php.net/manual/en/function.openssl-pkey-export.php
[3] https://wiki.dovecot.org/Plugins/MailCrypt#EC_key
[4] https://github.com/phpseclib/phpseclib
[5] https://github.com/sop/pkcs8