SKien\PNServer\PNEncryption::encrypt()

Complexity

Conditions	8
Paths	21

Size

Total Lines	71
Code Lines	33

Duplication

Lines	0
Ratio	0 %

Importance

Changes	1
Bugs	1	Features	0

<?php
    public function encrypt(string $strPayload)
    {
        $this->strError = '';
        $this->strPayload = $strPayload;
        $strContent = false;

        // there's nothing to encrypt without payload...
        if (strlen($strPayload) == 0) {
            // it's OK - just set content-length of request to 0!
            return '';
        }

        if ($this->strEncoding !== 'aesgcm' && $this->strEncoding !== 'aes128gcm') {
            $this->strError = "Encoding '" . $this->strEncoding . "' is not supported!";
            return false;
        }

        if (mb_strlen($this->strSubscrKey, '8bit') !== 65) {
            $this->strError = "Invalid client public key length!";
            return false;
        }

        try {
            // create random salt and local key pair
            $this->strSalt = \random_bytes(16);
            if (!$this->createLocalKey()) {
                return false;
            }

            // create shared secret between local private key and public subscription key
            $strSharedSecret = $this->getSharedSecret();

            // context and pseudo random key (PRK) to create content encryption key (CEK) and nonce
            /*
             * A nonce is a value that prevents replay attacks as it should only be used once.
             * The content encryption key (CEK) is the key that will ultimately be used toencrypt
             * our payload.
             * @link https://en.wikipedia.org/wiki/Cryptographic_nonce
             */
            $context = $this->createContext();
            $prk = $this->getPRK($strSharedSecret);

            // derive the encryption key
            $cekInfo = $this->createInfo($this->strEncoding, $context);
            $cek = self::hkdf($this->strSalt, $prk, $cekInfo, 16);

            // and the nonce
            $nonceInfo = $this->createInfo('nonce', $context);
            $nonce = self::hkdf($this->strSalt, $prk, $nonceInfo, 12);

            // pad payload ... from now payload converted to binary string
            $strPayload = $this->padPayload($strPayload, self::MAX_COMPATIBILITY_PAYLOAD_LENGTH);

            // encrypt
            // "The additional data passed to each invocation of AEAD_AES_128_GCM is a zero-length octet sequence."
            $strTag = '';
            $strEncrypted = openssl_encrypt($strPayload, 'aes-128-gcm', $cek, OPENSSL_RAW_DATA, $nonce, $strTag);

            // base64URL encode salt and local public key (for aes128gcm they are needed in binary form)
            if ($this->strEncoding === 'aesgcm') {
                $this->strSalt = self::encodeBase64URL($this->strSalt);
                $this->strLocalPublicKey = self::encodeBase64URL($this->strLocalPublicKey);
            }

            $strContent = $this->getContentCodingHeader() . $strEncrypted . $strTag;
        } catch (\RuntimeException $e) {
            $this->strError = $e->getMessage();
            $strContent = false;
        }

        return $strContent;
    }