I have some pictures files encrypted in windows. When I transferred that encrypted files in android, the mobile show them as normal without decrypt. With this the purpose of encryption becomes vain. What is the reason behind this and how can we secure our personal data with encryption?
What encryption are you using and if you try and open the files, are they viewable? If you are using the Windows EFS and you copy the file over to the android phone, windows decrypts the files on the fly for viewing and copying. The copy on the android device is no longer encrypted.
You could use something like true crypt to create an encrypted container and you would be able to transfer it and still be required to enter a password however I don't know that it would be viewable on android
i am using EFS. It is vieweable in mobile when i copy the encrypted file in android. Actually i want that with encryption the files open only in my pc and no one can see it by copying in to their computer.
EFS only does data at rest encryption. Meaning while it is on your hard drive it is encrypted. If someone took your hard drive out and tried to look at the data they could not. When you access that data Windows does on the fly decryption because the key is based on your Windows SID. If you copy the encrypted files to your android device or any other storage media Windows does the same thing. On the fly decryption and then copies the data. Even many full disk encryption solutions won't keep the data encrypted if you copy it unless you go with a enterprise product such as Checkpoint Encryption or Sophos Encryption which can be configured with a policy to prevent copying to storage media without encrypting the media. You could , like a said, use True Crypt or Vera Crypt to create encrypted containers and put your data in them. If those containers get copied they stay encrypted.
If you only use Windows and you have either Windows Pro or enterprise you can also create an attach a VHD file (virtual hard drive), mount it to a unused drive letter and then use bitlocker to encrypt the VHD file. So if someone steals the file it will still be encrypted.