注册机（英语：Keygen或Keymaker），又称序号机、序号产生器、注册码生成器、串行号生成器，为一种可破解商业软件注册进程之程序。

大部分注册机可根据用户输入注册内容来生成对应注册序号或注册文件。与此同时，也有很多程序不需输入用户名或其他信息即可获得注册时所需之序号。制作注册机者多为黑客或少数本地化作者。一般需要脱壳软件、内存查看软件和反汇编器等破解工具作为辅助。

为维护自身权益，部份软件公司采用机器码或软件分试用版和商业版等方式，以抵制注册机。同时某些新发行软件使用启动机制以试图阻止盗版，然而仍遭注册机破解。

A key generator (key-gen) is a computer program that generates a product licensing key, such as a serial number, necessary to activate for use a software application. Keygens may be legitimately distributed by software manufacturers for licensing software in commercial environments where software has been licensed in bulk for an entire site or enterprise, or they may be distributed illegitimately in circumstances of copyright infringement or software piracy. Illegitimate key generators are typically distributed by software crackers in the warez scene and demoscene, where keygens are often accompanied with chiptunes and artistic visual representations.