Bitpay\PrivateKey::pemEncode PHP Method

    public function pemEncode($keypair)
    {
        if (is_array($keypair) && (strlen($keypair[0]) < 64 || strlen($keypair[1]) < 128)) {
            throw new \Exception('Invalid or corrupt secp256k1 keypair provided. Cannot decode the supplied PEM data.');
        }
        $dec = '';
        $byte = '';
        $beg_ec_text = '';
        $end_ec_text = '';
        $ecpemstruct = array();
        $digits = array();
        for ($x = 0; $x < 256; $x++) {
            $digits[$x] = chr($x);
        }
        $ecpemstruct = array('sequence_beg' => '30', 'total_len' => '74', 'int_sec_beg' => '02', 'int_sec_len' => '01', 'int_sec_val' => '01', 'oct_sec_beg' => '04', 'oct_sec_len' => '20', 'oct_sec_val' => $keypair[0], 'a0_ele_beg' => 'a0', 'a0_ele_len' => '07', 'obj_id_beg' => '06', 'obj_id_len' => '05', 'obj_id_val' => '2b8104000a', 'a1_ele_beg' => 'a1', 'a1_ele_len' => '44', 'bit_str_beg' => '03', 'bit_str_len' => '42', 'bit_str_val' => '00' . $keypair[1]);
        $beg_ec_text = '-----BEGIN EC PRIVATE KEY-----';
        $end_ec_text = '-----END EC PRIVATE KEY-----';
        $dec = trim(implode($ecpemstruct));
        if (strlen($dec) < 230) {
            throw new \Exception('Invalid or corrupt secp256k1 keypair provided. Cannot encode the supplied data.');
        }
        $dec = Util::decodeHex('0x' . $dec);
        while (Math::cmp($dec, '0') > 0) {
            $dv = Math::div($dec, '256');
            $rem = Math::mod($dec, '256');
            $dec = $dv;
            $byte = $byte . $digits[$rem];
        }
        $byte = $beg_ec_text . "\r\n" . chunk_split(base64_encode(strrev($byte)), 64) . $end_ec_text;
        $this->pemEncoded = $byte;
        return $byte;
    }