<?php

/*
	This file is part of the ParTCP PHP Library project
	Copyright (C) 2023 Martin Wandelt

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU Affero General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Affero General Public License for more details.

	You should have received a copy of the GNU Affero General Public License
	along with this program.  If not, see <https://www.gnu.org/licenses/>
*/

class ParTCP_Crypto {

	static $privKeySign;
	static $privKeyCrypt;
	static $remoteKeySign;
	static $remoteKeyCrypt;
	static $useLegacyKx = FALSE;
	static $errors;


	static function get_signature_length(){
		return 88;
	}


	static function get_pubkey_length(){
		return 88;
	}


	static function get_privkey_length(){
		return 128;
	}


	static function generate_keys( $setLocalPrivKey = FALSE ){
		$keyPair = sodium_crypto_sign_keypair();
		$privKeySign = sodium_crypto_sign_secretkey( $keyPair );
		$pubKeySign = sodium_crypto_sign_publickey( $keyPair );
		$keyPair = sodium_crypto_box_keypair();
		$privKeyCrypt = sodium_crypto_box_secretkey( $keyPair );
		$pubKeyCrypt = sodium_crypto_box_publickey( $keyPair );
		$keys = [
			base64_encode( $pubKeySign . $pubKeyCrypt ),
			base64_encode( $privKeySign . $privKeyCrypt ),
		];
		if ( $setLocalPrivKey ){
			self::$privKeySign = $privKeySign;
			self::$privKeyCrypt = $privKeyCrypt;
		}
		return $keys;
	}


	static function set_remote_pubkey( $key ){
		if ( strlen( $key ) != self::get_pubkey_length() ){
			throw new Exception('Invalid public key length ' . strlen( $key ) );
		}
		$key = base64_decode( $key );
		self::$remoteKeySign = substr( $key, 0, SODIUM_CRYPTO_SIGN_PUBLICKEYBYTES );
		self::$remoteKeyCrypt = substr( $key, SODIUM_CRYPTO_SIGN_PUBLICKEYBYTES );
	}


	static function set_local_privkey( $key ){
		if ( strlen( $key ) != self::get_privkey_length() ){
			throw new Exception('Invalid private key length ' . strlen( $key ) );
		}
		$key = base64_decode( $key );
		self::$privKeySign = substr( $key, 0, SODIUM_CRYPTO_SIGN_SECRETKEYBYTES );
		self::$privKeyCrypt = substr( $key, SODIUM_CRYPTO_SIGN_SECRETKEYBYTES );
	}


	static function generate_private_hash( $data ){
		if ( ! self::$privKeySign ){
			throw new Exception('No private key for signing specified');
		}
		$hash = hash( 'sha256', $data . self::$privKeySign );
		return base64_encode( $hash );
	}


	static function generate_signature( $data ){
		if ( ! self::$privKeySign ){
			throw new Exception('No private key for signing specified');
		}
		$data = str_replace( ["\r\n", "\r"], "\n", trim( $data ) );
		$signature = sodium_crypto_sign_detached( $data, self::$privKeySign );
		return base64_encode( $signature );
	}


	static function verify_signature( $signature, $data ){
		if ( ! self::$remoteKeySign ){
			throw new Exception('No remote key specified');
		}
		if ( strlen( $signature ) != self::get_signature_length() ){
			throw new Exception('Invalid signature length');
		}
		$data = str_replace( ["\r\n", "\r"], "\n", trim( $data ) );
		$signature = base64_decode( $signature );
		$result = sodium_crypto_sign_verify_detached( $signature, $data,
			self::$remoteKeySign );
		if ( $result != 1 ){
			return FALSE;
		}
		return TRUE;
	}


	static function encrypt( $data ){
		if ( ! self::$privKeyCrypt ){
			throw new Exception('No private key for encryption specified');
		}
		if ( ! self::$remoteKeyCrypt ){
			throw new Exception('No remote key specified');
		}
		$iv = openssl_random_pseudo_bytes( 16 );
		$secret = sodium_crypto_scalarmult( self::$privKeyCrypt, self::$remoteKeyCrypt );
		if ( self::$useLegacyKx ){
			$encrypted = openssl_encrypt( $data, 'aes-256-ctr', $secret, 0, $iv );
		}
		else {
			$secret = hash( 'sha256', $secret, TRUE );
			$encrypted = openssl_encrypt( $data, 'aes-256-cbc', $secret, 0, $iv );
		}
		return base64_encode( $iv ) . ':' . $encrypted;
	}


	static function decrypt( $data ){
		if ( ! self::$privKeyCrypt ){
			throw new Exception('No private key for encryption specified');
		}
		if ( ! self::$remoteKeyCrypt ){
			throw new Exception('No remote key specified');
		}
		list( $iv, $encrypted ) = explode( ':', $data ) + [ '', '' ];
		$iv = base64_decode( $iv );
		if ( ! $iv || strlen( $iv ) != 16 ){
			throw new Exception('Missing or invalid initialization vector');
		}
		$secret = sodium_crypto_scalarmult( self::$privKeyCrypt, self::$remoteKeyCrypt );
		if ( self::$useLegacyKx ){
			$decrypted = openssl_decrypt( $encrypted, 'aes-256-ctr', $secret, 0, $iv );
		}
		else {
			$secret = hash( 'sha256', $secret, TRUE );
			$decrypted = openssl_decrypt( $encrypted, 'aes-256-cbc', $secret, 0, $iv );
		}
		if ( $decrypted === FALSE ){
			while ( $msg = openssl_error_string() ){
				self::$errors[] = $msg;
			}
		}
		return $decrypted;
	}

}

// end of file crypto.class.php