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@@ -9,4 +9,19 @@ Similarly a Key in GnuPG is called a KeyRing in BC/PGPainless. This is due to th
 |-------------------|----------------|--------------------------------------------------------------------------|
 | KeyRingCollection | KeyRing/KeyBox | Collection of OpenPGP keys (either of a single user or of multiple users |
 | KeyRing           | Key            | Master key which might have sub keys                                     |
-| Key               |                | Single key which might be a master key or a sub key                      |
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+| Key               |                | Single key which might be a master key or a sub key                      |
+
+## Public, Secret, Private
+
+In GnuPG, the terms PrivateKey and SecretKey are mostly used as synonyms. In Bouncycastle there is a distinction.
+A PGPSecretKey names a private key which might be encrypted with a password. From the PGPSecretKey the private key can be obtained by providing the password. The PGPPrivateKey is never encrypted. It is possible to obtain a PGPPublicKey from a PGPSecretKey.
+
+| PGPainless Term            | Description                                                    |
+|----------------------------|----------------------------------------------------------------|
+| PGPPrivateKey              | Decrypted OpenPGP private key                                  |
+| PGPSecretKey               | (Possibly) password protected OpenPGP private key              |
+| PGPPublicKey               | OpenPGP public key                                             |
+| PGPSecretKeyRing           | (Possibly) password protected private master key with sub keys |
+| PGPPublicKeyRing           | OpenPGP public master key with public sub keys                 |
+| PGPSecretKeyRingCollection | Collection of PGPSecretKeyRings                                |
+| PGPPublicKeyRingCollection | Collection of PGPPublicKeyRings                                |
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