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    quickstart.md
    pgpainless-cli/usage.md
    sop.md
-   pgpainless-core/indepth.rst
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+   pgpainless-core/indepth.rst
+   pgpainless-core/migration_2.0.md
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diff --git a/docs/source/pgpainless-core/migration_2.0.md b/docs/source/pgpainless-core/migration_2.0.md
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+# Migration Guide PGPainless 2.0
+
+PGPainless 2.0 makes use of Bouncy Castles new High Level API.
+As a consequence, the use of certain "mid-level" classes, such as `PGPPublicKeyRing`, `PGPSecretKeyRing` is now
+discouraged in favor of their high-level counterparts, e.g. `OpenPGPCertificate`, `OpenPGPKey`.
+
+## Terminology Changes
+
+Bouncy Castles high level API uses OpenPGP terminology as described in the book [OpenPGP for application developers](https://openpgp.dev/book/).
+Therefore, some terms used in the mid-level API are no longer used.
+
+| Old Term        | New Term                   | Description                                          |
+|-----------------|----------------------------|------------------------------------------------------|
+| key ring        | OpenPGP certificate or key |                                                      |
+| public key ring | certificate                |                                                      |
+| secret key ring | key                        |                                                      |
+| subkey          | component key              | A component key is either a primary key, or a subkey |
+
+
+## Key Material
+
+The use of `PGPPublicKeyRing` objects is now discouraged in favor of `OpenPGPCertificate`.
+Appropriately, `OpenPGPKey` replaces `PGPSecretKeyRing`. `OpenPGPKey` extends the `OpenPGPCertificate` class, but also
+contains secret key material.
+
+An `OpenPGPCertificate` consists of `OpenPGPComponentSignature`s and `OpenPGPCertificateComponent`s,
+such as `OpenPGPComponentKey`s and `OpenPGPIdentityComponent`s.
+`OpenPGPIdentityComponent`s are either `OpenPGPUserId`s or `OpenPGPUserAttribute`s.
+Components of an OpenPGP certificate, which contain key material (public keys, secret keys, subkeys...) are represented
+by the `OpenPGPComponentKey` class, from which `OpenPGPPrimaryKey`, `OpenPGPSubkey` and `OpenPGPSecretKey` inherit.
+
+`OpenPGPCertificateComponent`s are bound to the certificate by `OpenPGPSignature`s, which Bouncy Castle organizes into
+`OpenPGPSignatureChains` internally.
+
+## `KeyIdentifier`
+OpenPGP has evolved over time and with it the way to identify individual keys.
+Old protocol versions rely on 64-bit key-ids, which are nowadays deprecated, as 64-bits are not exactly collision-resistant.
+For some time already, the use of fingerprints is therefore encouraged as a replacement.
+However, key-ids were not everywhere at once in the protocol, so many artifacts still contain elements with key-ids in them.
+An example for this are public-key encrypted session-key packets, which in version 1 still only contain the recipients
+key-id.
+In signatures, both key-ids and fingerprints are present.
+
+To solve this inconsistency, Bouncy Castle introduced the `KeyIdentifier` type as an abstraction of both key-ids and fingerprints.
+Now most methods that take some sort of identifier, be it fingerprint or key-id, now also accept a `KeyIdentifier` object.
+
+Consequently, `KeyIdentifier` is now also the preferred way to reference keys in PGPainless and many places where previously
+a key-id or fingerprint was exepcted, now also accept `KeyIdentifier` objects.
+
+## Differences between BCs high level API and PGPainless
+
+With Bouncy Castle now introducing its own high-level API, you might ask, what differences there are between
+high-level PGPainless classes and their new Bouncy Castle counterparts.
+
+### `KeyRingInfo` vs. `OpenPGPCertificate`/`OpenPGPKey`
+
+PGPainless' `KeyRingInfo` class fulfils a similar task as the new `OpenPGPCertificate`/`OpenPGPKey` classes,
+namely evaluating OpenPGP key material, checking self signatures, exposing certain properties like
+subkeys, algorithm preferences etc. in a way accessible for the user, all with respect to a given reference time.
+
+However, `KeyRingInfo` historically gets instantiated *per reference time*, while`OpenPGPCertificate`/`OpenPGPKey`
+is instantiated only *once* and expects you to pass in the reference time each time you are using a
+property getter, lazily evaluating applicable signatures as needed.
+Under the hood, the Bouncy Castle classes now cache expensive signature verification results for later use.
+Consequently, `KeyRingInfo` now wraps `OpenPGPCertificate`/`OpenPGPKey`, forwarding method calls while passing along
+the chosen reference time and mapping basic data types to PGPainless' high level types / enums.
+
+## Replacements
+
+| Old                          | New                   | Comment                                                             |
+|------------------------------|-----------------------|---------------------------------------------------------------------|
+| `PGPPublicKeyRing`           | `OpenPGPCertificate`  | Self-Signatures are automagically evaluated                         |
+| `PGPSecretKeyRing`           | `OpenPGPKey`          | Same as `OpenPGPCertificate`, but also contains secret key material |
+| `PGPPublicKey` (primary key) | `OpenPGPPrimaryKey`   | -                                                                   |
+| `PGPPublicKey` (subkey)      | `OpenPGPComponentKey` | -                                                                   |
+| `PGPSecretKey` (primary key) | `OpenPGPSecretKey`    | -                                                                   |
+| `PGPSecretKey` (subkey)      | `OpenPGPSecretKey`    | -                                                                   |
+| `PGPPrivateKey`              | `OpenPGPPrivateKey`   | -                                                                   |
+| `Long` (Key-ID)              | `KeyIdentifier`       | -                                                                   |
+| `byte[]` (Key Fingerprint)   | `KeyIdentifier`       | -                                                                   |
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