====== PHP RFC: Simple Cryptography Library ======
  * Version: 0.1
  * Date: 2016-01-09
  * Author: Scott Arciszewski, security@paragonie.com
  * Status: Draft
  * First Published at: https://wiki.php.net/rfc/php71-crypto

===== Introduction =====
Cryptography is hard to get right, even for experts. Building atop the victories against insecure design that the password hashing API have brought us, I would seek to provide a simple, secure-by-default cryptography interface that puts as little burden on the user (PHP developers) as possible, that works with multiple cryptography backends.

===== Proposal =====

My proposal is to create a series of new classes (preferably in its own namespace, e.g. \Php\Crypto or simply \Cryptography):

  * ''Asymmetric\Crypto''
  * ''Asymmetric\EncryptionSecretKey''
  * ''Asymmetric\EncryptionPublicKey''
  * ''Asymmetric\SignatureSecretKey''
  * ''Asymmetric\SignaturePublicKey''
  * ''Symmetric\AuthenticationKey''
  * ''Symmetric\Crypto''
  * ''Symmetric\EncryptionKey''
  * ''Key'' (base type that all *Key classes inherit from)
  * ''KeyFactory'' (abstract class, static methods)
  * ''KeyPair''

Users would primarily be interested in the ''Crypto'' classes, and the methods of the ''KeyFactory'' class.

For example:

    $keypair = \Php\Crypto\KeyFactory::generateEncryptionKeyPair('openssl'); 
    var_dump($keypair); // An instance of \Php\Crypto\KeyPair
    $secret = $keypair->getSecretKey(); // \Php\Crypto\Asymmetric\EncryptionSecretKey
    $public = $keypair->getPublicKey(); // \Php\Crypto\Asymmetric\EncryptionPublicKey
    
    $fips = new \Php\Crypto\Asymmetric\Crypto([
        'driver' => 'openssl',
        'cipher' => 'aes-256',
        'hash' => 'sha384'
    ]);
    $ciphertext = $fips->seal(
        'This is a text message',
        $public
    );
    $plaintext = $fips->unseal(
        $ciphertext,
        $secret
    );
    var_dump($plaintext === 'This is a text message'); // bool(true)

The ''Asymmetric\Crypto'' interface would look like this:
  
  * ''string'' ''encrypt( string, EncryptionSecretKey, EncryptionPublicKey )''
  * ''string'' ''decrypt( string, EncryptionSecretKey, EncryptionPublicKey )''
  * ''string'' ''seal( string, EncryptionPublicKey )''
  * ''string'' ''unseal( string, EncryptionSecretKey )''
  * ''string'' ''sign( string, SignatureSecretKey )''
  * ''bool' ''verify( string, SignaturePublicKey, string )''

The ''Symmetric\Crypto'' interface would look like this:

  * ''string'' ''auth( string, AuthenticationKey )''
  * ''bool'' ''verify( string, AuthenticationKey )''
  * ''string'' ''aeadEncrypt( string, EncryptionKey, string )''
  * ''string'' ''aeadDecrypt( string, EncryptionKey, string )''
  * ''string'' ''encrypt( string, EncryptionKey )''
  * ''string'' ''decrypt( string, EncryptionKey )''

All decryption (including unseal()) operations will throw a typed exception (e.g. ''\Php\Crypto\CryptoException'') if the MAC doesn't validate.

===== Drivers, Configurations, and Defaults =====

This API will act similar to PDO in the sense that it can, behind the scenes, support multiple drivers. As of the day we ship PHP 7.1.0, we MUST support at least two:

  * ''libsodium''
  * ''openssl''

Which driver and which primitives can be supplied at the time a Crypto object is created, but the valid choices will be limited.

  * Libsodium (not configurable)
    * Cipher: Xsalsa20
    * Hash/HMAC: HMAC-SHA-512/256
    * Public keys: X25519
    * Signatures: Ed25519
    * HKDF: BLAKE2b
    * Password-Based Key Derivation: Argon2i
  * OpenSSL (configurable):
      * Cipher: AES-128, AES-192, AES-256
      * Hash/HMAC: SHA256, SHA384, SHA512, SHA3-356, SHA3-384, SHA3-512
      * Public keys: ECDH over NIST P-256
      * Signatures: ECDSA over NIST P-256
      * HKDF: (See hash function above)
      * Password-Based Key Derivation: PBKDF2-(hash function above) with 86,000 rounds

If both drivers are installed, both ''Crypto'' classes will default to libsodium (reason: secure defaults) unless otherwise specified.

If you only specify a driver, OpenSSL will default to: AES-256 and SHA-384. Only CTR mode is supported regardless of cipher, except for aeadEncrypt() and aeadDecrypt(), which should only allow GCM mode.

===== Ciphertext Message Format =====

The first four bytes of any message are a header that indicates the version of the library and various other information.

  * First byte: Major version of this interface (e.g. ''01'')
  * Second byte: Minor version of this interface (e.g. ''05'')
  * Third byte: Driver ID
  * Fourth byte: A checksum (''Byte0 ^ Byte1 ^ Byte2'') to detect corruption

Driver-specific metadata can follow this four-byte header, but it is not required.

===== Proposed PHP Version(s) =====

This should be considered for inclusion in PHP 7.1

===== RFC Impact =====

==== To Existing Extensions ====

===== Unaffected PHP Functionality =====



===== Future Scope =====

===== Proposed Voting Choices =====

This is a new feature; would a 50%+1 majority be acceptable?

===== Patches and Tests =====

A prototype is available here, which fleshed out a lot of the ideas: https://github.com/paragonie/pco_prototype

===== Implementation =====



===== References =====



===== Rejected Features =====