Now, we need to generate signing certificate to sign android apk. Following is the command to generate a signing certificate. You need to execute this command in the terminal and this will generate flutter_release_apk.jks file in the same folder where terminal opened.
keytool -genkey -v -keystore flutter_release_apk.jks -alias alias_name -keyalg RSA -keysize 2048 -validity 10000
Enter keystore password: abcd1234
Re-enter new password: abcd1234
What is your first and last name?
[Unknown]: demo demo
What is the name of your organizational unit?
[Unknown]: demo
What is the name of your organization?
[Unknown]: demo
What is the name of your City or Locality?
[Unknown]: demo
What is the name of your State or Province?
[Unknown]: demo
What is the two-letter country code for this unit?
[Unknown]: 91
Is CN=demo demo, OU=demo, O=demo, L=demo, ST=demo, C=91 correct?
[no]: yes
Generating 2,048 bit RSA key pair and self-signed certificate (SHA256withRSA) with a validity of 10,000 days
for: CN=demo demo, OU=demo, O=demo, L=demo, ST=demo, C=91
Enter key password for <alias_name>
(RETURN if same as keystore password): abcd1234
Re-enter new password: abcd1234
[Storing flutter_release_apk.jks]
So, now I have my flutter_release_apk.jksin directory where my terminal is open.
NOTE
Copy and Save this file safely because it is required every time you need to update your app. If you lose this file then there is no way to update your app in future