使用Xcode给iPhone做虚拟地址，或者开发时，编译时有时会遇到证书相关的错误：
Warning: unable to build chain to self-signed root for signer "Mac Developer: Dylan M (*******)"
解决方法：
1. 首先可以尝试Lock all cerficates
a. 打开 Keychain Access
b. File->Lock All Keychains
c. 运行Xcode的工程，访问到证书时重新输入密码
2. 如果第一种方法失败，按下面的提示去下载一个证书，然后clean Xcode的工程，重新编译，通过
If none of the above works, download the WWDR Intermediate Certificate and drag and drop into your 'System' keychain. Don't put it in 'login' - I tried that myself and it did nothing to help me. Try to avoid changing the trust settings of your certificates, Xcode gave me a warning when it saw I had modified my development certificate's trust settings.
