How android writes a signature and its Functions

What is a signature? And why signature?
Today, I am very careful to share with you.
What is a signature? After writing the application, You Need To package, sign, and publish it. All Android applications require developers to use a certificate for digital signature. The private key of the certificate is owned by developers.
Signature function: (1) identity authentication of the sender
(2) ensure the integrity of input information
(3) prevent the occurrence of credit in the transaction
Market Requirements for software: the same package name and different signatures cannot overwrite the installation, and the same package name and signature can overwrite the installation.
To write a signature, follow these steps:
1) Right-click Android Tools in an Eclipse Android project and select Export Signed Application Package
2) Select a project and click next
3) Select create, set the Save path and file name of the signature file, and enter the signature file Password.
4) Fill in relevant information
5) Select the path to save the signature apk.
6) directly finish, and then OK.

This article is from "android Diary"