Add information on how to use hybrid cryptography (#29)

README.md

@@ -18,14 +18,14 @@ brew install nakabonne/pbgopy/pbgopy
 #### RHEL/CentOS
 
 ```
-rpm -ivh https://github.com/nakabonne/pbgopy/releases/download/v0.2.1/pbgopy_0.2.1_linux_amd64.rpm
+rpm -ivh https://github.com/nakabonne/pbgopy/releases/download/v0.3.0/pbgopy_0.3.0_linux_amd64.rpm
 ```
 
 #### Debian/Ubuntu
 
 ```
-wget https://github.com/nakabonne/pbgopy/releases/download/v0.2.1/pbgopy_0.2.1_linux_amd64.deb
-apt install ./pbgopy_0.2.1_linux_amd64.deb
+wget https://github.com/nakabonne/pbgopy/releases/download/v0.3.0/pbgopy_0.3.0_linux_amd64.deb
+apt install ./pbgopy_0.3.0_linux_amd64.deb
 ```
 
 #### Arch Linux
@@ -79,49 +79,77 @@ pbgopy paste >foo.png
 ## Options
 
 ### End-to-end encryption
-`pbgopy` comes with a built-in ability to encrypt/decrypt with a symmetric-key. Hence allows you to perform end-to-end encryption without working with external tools.
+`pbgopy` comes with a built-in ability to encrypt/decrypt with a variety of keys.
 
-You can derive the key from password with the `-p` flag.
+#### With symmetric-key
 
+You can derive the key from password with the `-p` flag, which is provided so that you can encrypt/decrypt without previous setting.
 ```bash
-pbgopy copy -p your-password <secret.txt
+pbgopy copy -p your-password <plaintext.txt
 ```
 
 ```bash
 pbgopy paste -p your-password
 ```
 
-This flag is provided so that you can encrypt/decrypt without previous setting. Be aware that this way cannot prevent a dictionary attack.
+Be aware that this way cannot prevent a dictionary attack.
 
 For more safety, it is highly recommended to use a 32-bytes symmetric key generated by other methods.
 The `-k` flag or the `PBGOPY_SYMMETRIC_KEY_FILE` environment variable is available to indicate the path to key file.
 
 ```bash
-pbgopy copy -k /path/to/pbgopy.key <secret.txt
+pbgopy copy -k /path/to/pbgopy.key <plaintext.txt
 ```
 
-### Authentication
-HTTP Basic Authentication is available with `-a` flag.
+#### With public/private key-pair
+`pbgopy` can also encrypt using hybrid cryptosystem. If you have already exchanged public keys between devices you want to share data with, this is the way to go.
 
 ```bash
-pbgopy serve -a user:pass
+pbgopy copy --public-key-file /path/to/public.key <plaintext.txt
 ```
 
 ```bash
-pbgopy copy -a user:pass <foo.png
+pbgopy paste --private-key-file /path/to/private.key <plaintext.txt
 ```
 
+You manage your keyring in GPG? The `--gpg-user-id` (`-u`) flag is for you!
+Suppose you want to encrypt with a public key whose user id is `alice`:
+
 ```bash
-pbgopy paste -a user:pass >foo.png
+pbgopy copy -u alice <plaintext.txt
 ```
 
+Then you decrypt it with the private key by specifying the user id on another device:
+
+```bash
+pbgopy paste -u alice
+```
+
+There are a couple of ways to specify a user ID. Visit [here](https://www.gnupg.org/documentation/manuals/gnupg/Specify-a-User-ID.html) to see the entire list.
+
 ### TTL
-You can set TTL for the cache. Give `0s` for disabling it. Default is `24h`.
+If you don't want more data to be cached on the server than necessary, use the `--ttl` flag to set TTL for the cache.
+Give `0s` for disabling it. Default is `24h`.
 
 ```bash
 pbgopy serve --ttl 10m
 ```
 
+### Authentication
+HTTP Basic Authentication is available with `-a` flag.
+
+```bash
+pbgopy serve -a user:pass
+```
+
+```bash
+pbgopy copy -a user:pass <foo.png
+```
+
+```bash
+pbgopy paste -a user:pass >foo.png
+```
+
 ### From clipboard on your OS
 You can put the data stored at the clipboard on your OS into pbgopy server.