*.cer 文件通常只包含证书，而不包含签署 APK 所需的私钥.

*.cer files usually only contain certificates, not the private key needed to sign an APK.

列出密钥库的内容:

keytool -list -v -keystore my_keystore.keystore

并寻找 Entry type: 行(对应的别名).该值必须是 PrivateKeyEntry，而不是 trustedCertEntry

And look for the Entry type: line (for the corresponding alias). The value must be PrivateKeyEntry, not trustedCertEntry