Update OpenSSL Extension to Support KEMs

OpenSSL 3 introduced a KEM API, which is an abstraction for the kinds of cryptographic operations used by the NIST post-quantum cryptography standards (i.e., FIPS-203). KEM stands for "Key Encapsulation Mechanism". It's the preferred way to do asymmetric cryptography. Even RSA-KEM is safer than how most people experience RSA encryption. The relevant functions are EVP_PKEY_encapsulate() and EVP_PKEY_decapsulate(). https://github.com/openssl/openssl/blob/4b4333ffcc8e4ecbf5c70214769c77c7a1bb684f/crypto/evp/kem.c#L225 https://github.com/openssl/openssl/blob/4b4333ffcc8e4ecbf5c70214769c77c7a1bb684f/crypto/evp/kem.c#L262 Currently, these APIs only seem to support classical cryptography (ECC, RSA), but that is one of the APIs that will enable post-quantum cryptography for software using OpenSSL in the future. We intend to send a pull request later this year to include PHP functions in the OpenSSL extension that look like this: function openssl_kem_encaps(OpenSSLAsymmetricKey $pk): array; // 0 -> shared secret (typically 32 bytes) // 1 -> KEM ciphertext for decaps function openssl_kem_decaps(OpenSSLAsymmetricKey $sk, string $kemCiphertext): string; // Returns a shared secret or throws an exception upon decryption failure. I don't know if this change needs an RFC or not, but I wanted to start the discussion just in case. Security Team Paragon Initiative Enterprises <https://paragonie.com/security>