使用3des算法，加密模式：CBC，填充：pkcs5padding

/**
 * 3DES加解密类
 */
class Des3phpService
{
    //加密秘钥(base64加密)
    private $key ;
    //初始偏移向量
    private $iv;

    /**
     * 构造，传递二个已经进行base64_encode的KEY与IV
     *
     * @param string $key
     * @param string $iv
     */
    public function __construct($key, $iv)
    {
        $this->iv = $iv;
        $this->key = $key;
    }

    //填充加密快的大小
    public function pkcs5_pad($text, $blocksize)
    {
        $padding_char = $blocksize - (strlen($text) % $blocksize);
        $text .= str_repeat(chr($padding_char), $padding_char);
        return $text;
    }

    //解密
    public function decrypt($encrypted)
    {
        $key = $this->key;
        $encrypted = base64_decode($encrypted);
        $size = openssl_cipher_iv_length("DES-EDE3-CBC");
        if ($this->iv == "") {
            $iv = openssl_random_pseudo_bytes($size);
        } else {
            $iv = $this->iv;
        }
        $rs = openssl_decrypt($encrypted, "DES-EDE3-CBC", $key, OPENSSL_RAW_DATA | OPENSSL_NO_PADDING, $iv);
        $rs = $this->pkcs5_unpad($rs);
        return $rs;
    }

    //加密
    public function encrypt($input)
    {
        $key =$this->key;
        $size = openssl_cipher_iv_length("DES-EDE3-CBC");
        $input = $this->pkcs5_pad($input, $size);
        $rs = openssl_encrypt($input, "DES-EDE3-CBC", $key, OPENSSL_RAW_DATA | OPENSSL_NO_PADDING, $this->iv);
        $rs = base64_encode($rs);
        return $rs;
    }


    public function pkcs5_unpad($text)
    {
        $pad = ord($text[strlen($text) - 1]);
        if ($pad > strlen($text)) {
            return false;
        }
        if (strspn($text, chr($pad), strlen($text) - $pad) != $pad) {
            return false;
        }
        return substr($text, 0, -1 * $pad);
    }
}
$key = 'abcdefgh12345678abcdefgh';
$iv = '12345678';
$des = new Des3phpService($key, $iv);
$str = "api";
echo "source: {$str},len: ", strlen($str), "\r\n";
$e_str = $des->encrypt($str);
echo "entrypt: ", $e_str, "\r\n";
$d_str = $des->decrypt($e_str);
echo "dntrypt: {$d_str},len: ", strlen($d_str), "\r\n";
# 明文='api';
# 密文='eH89ioIVp/Y='