High-Level OpenPGP API

[vanitasvitae]

This PR contains a high-level API for OpenPGP, which simplifies the following tasks:

• Message Creation
  • OpenPGPMessageGenerator sets up an OpenPGPMessageOutputStream based on user configuration
• Message Consumption
  • OpenPGPMessageProcessor processes encrypted / signed / compressed OpenPGP messages and emits the plaintext along with metadata
• Certificate / Key Evaluation
  • OpenPGPCertificate acts as high-level API pendant to PGPPublicKeyRing, evaluating expiration / revocation / key signatures and allows the user to get verified information about the cert
  • OpenPGPKey provides similar high-level API pendant to PGPSecretKeyRing

I decided to use a common OpenPGP* naming scheme for the new HighLevel API classes and also decided to make use of general terminology from the book "OpenPGP for application developers" (https://openpgp.dev).

This PR is still pretty much very early work in progress (as is #1857, which will eventually integrate with this API), but I want you to be able to comment on it during the development phase already :)

[vanitasvitae]

This PR is now based on #1926

[vanitasvitae]

This PR contains #1931 and may need to be rebased if the other patch is merged.

[vanitasvitae]

@dghgit I noticed, that in many places you replaced

for (item : collection)
{

with

for (Iterator it = collection.iterator(); it.hasNext();)
{
    Item item = iterator.next();

I was under the impression that BC was now targeting Java 1.8 primarily, which already supports the former method of collection iteration.
Am I missing something? Why are the Iterators not using generics?

Edit: I see you recently made some changes for Java 4 and 5 compatibility.

[ligefeiBouncycastle]

@vanitasvitae Thank you for the update. I've reviewed the code and have merged the majority of it into the main branch — about 20 files remain to be merged. Two test classes, DoubleBufferedInputStreamTest and PGPKeyPairGeneratorTest, will be merged into master at a later stage. Please take a look at the latest changes on the main branch.

[vanitasvitae]

Looking good! Thank you for your work! :)
One thing: If its not too much of a hassle, I'd prefer if you keep the commit authorship intact :)

[ligefeiBouncycastle]

@vanitasvitae Apologies — the commit authorship information was lost during the branch merges (I had split the work across about 7 branches). I’ll do my best to recover and restore the original authorship.

[ligefeiBouncycastle]

@vanitasvitae Thank you for your greater contribution to this PR. Now all tests related to this PR have been merged with related code. The remaining classes include:
core/src/main/java/org/bouncycastle/util/Objects.java
pg/src/main/java/org/bouncycastle/openpgp/api/exception/PolicyException.java
pg/src/main/java/org/bouncycastle/openpgp/api/util/OpenPGPKeyPrinter.java
pg/src/main/java/org/bouncycastle/openpgp/api/EncryptedDataPacketType.java
pg/src/main/java/org/bouncycastle/openpgp/api/MessageEncryptionMechanism.java
pg/src/main/java/org/bouncycastle/openpgp/api/OpenPGPSignature.java
pg/src/main/java/org/bouncycastle/openpgp/PGPEncryptedDataList.java
pg/src/main/java/org/bouncycastle/openpgp/PGPKeyRing.java
pg/src/main/java/org/bouncycastle/openpgp/PGPKeyRingGenerator.java
pg/src/main/java/org/bouncycastle/openpgp/PGPPublicKey.java
pg/src/main/java/org/bouncycastle/openpgp/PGPSecretKey.java
pg/src/main/java/org/bouncycastle/openpgp/PGPSignatureSubpacketVector.java

Some of these classes will be merged later.

[vanitasvitae]

Nice!
Would it serve you if I rebased the remaining unmerged changes into smaller PRs?

[ligefeiBouncycastle]

@vanitasvitae Thank you! If you're planning to build new functionality that depends on the unmerged changes, feel free to break them into smaller PRs—this will help with quicker reviews and integration. Otherwise, I’ll take care of merging the remaining changes into the main branch later.