Thanks for your advice, I finally made pinentry_0.8.4-r0_core2-32.ipk.
I misunderstood how pinentry works. pinentry did not require GUI window and worked with terminal. That was good. But, generating key may be a too much burden for Edison. When gpg --gen-key started generating key after my entering passphrase, Edison's response became slow. After the key generation returned, Edison started acting strange. I rebooted Edison, but, it was still not responding correctly. I'm going to flash Edison.
Now, I realized I just needed encryption and decryption on Edison and I may be able to use a key that is generated somewhere else. So, I will create a key on my PC and try to use it with gpg on Edison.