# termux にて
$ mkdir ~/xxx
$ cd xxx
$ wget https://f-droid.org/FDroid.apk
$ wget https://f-droid.org/FDroid.apk.asc
$ pkg install gnupg
$ pkg install dirmngr

# とりあえず verify
$ gpg --verify FDroid.apk.asc FDroid.apk gpg: Signature made 2019-04-11 21:41:19 +0900 JST
gpg: using RSA key 7A029E54DD5DCE7A
gpg: Can't check signature: No public key

# 鍵取得 ... OK
$ gpg --keyserver keyserver.ubuntu.com --recv-keys 0x7A029E54DD5DCE7A
gpg: key 41E7044E1DBA2E89: 39 signatures not checked due to missing keys
gpg: /data/data/com.termux/files/home/.gnupg/trustdb.gpg: trustdb created
gpg: key 41E7044E1DBA2E89: public key "F-Droid <[email protected]>" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1

# verify ... Good signature 出たからOKかな
$ gpg --verify FDroid.apk.asc FDroid.apk
gpg: Signature made 2019-04-11 21:41:19 +0900 JST
gpg: using RSA key 7A029E54DD5DCE7A
gpg: Good signature from "F-Droid <[email protected]>" [unknown]
gpg: WARNING: This key is not certified with a trusted signature!
gpg: There is no indication that the signature belongs to the owner.
Primary key fingerprint: 37D2 C987 89D8 3119 4839 4E3E 41E7 044E 1DBA 2E89
Subkey fingerprint: 802A 9799 0161 1234 6E1F EFF4 7A02 9E54 DD5D CE7A