Encryption API 2.0

[vanitasvitae]

I noticed, that the builder pattern for the encryption/signing API was a bit complex and inflexible.
Most importantly, the user was expected to define which algorithms to use when encrypting. Furthermore sign-only operations would not allow change of algorithms at all (see #75).

This PR introduces a new API which moves options for signing and encrypting into separate builders.
Instead of calling

        EncryptionStream encryptor = PGPainless.encryptAndOrSign()
                .onOutputStream(envelope)
                .toRecipients(recipientPub)
                .usingAlgorithms(SymmetricKeyAlgorithm.AES_256, HashAlgorithm.SHA512, CompressionAlgorithm.ZIP)
                .signWith(keyDecryptor, senderSec)
                .signBinaryDocument()
                .noArmor();

the API has been simplified to

        EncryptionOptions encOpt = new EncryptionOptions()
                .addRecipient(recipientPub);
        SigningOptions signOpt = new SigningOptions()
                .addInlineSignature(keyDecryptor, senderSec, type);

        EncryptionStream encryptor = PGPainless.encryptAndOrSign()
                .onOutputStream(envelope)
                .withOptions(ProducerOptions
                        .signAndEncrypt(encOpt, signOpt)
                        .setAsciiArmor(armor));

The new API evaluates the keys used to sign/encrypt and automatically negotiates algorithms.
It is still possible to use custom algorithms though:

        encOpts.overrideEncryptionAlgorithm(AES_128);
        signOpts.overrideHashAlgorithm(SHA_256);
        prodOpts.overrideCompressionAlgorithm(UNCOMPRESSED);

Default algorithms and fallbacks can be controlled via PGPainless.getPolicy().

Lastly the new API also allows control over which subkeys are used for encryption.
Instead of encrypting to all available encryption subkeys of a keyring, the API will now per default only encrypt to the first encryption capable subkey that is being found.
This behaviour can for example be modified by calling

        encOpts.addRecipient(aliceKey, EncryptionOptions.encryptToAllCapableSubkeys())

Other implementations are possible by implementing EncryptionKeySelector.

All in all, the new API should be way more flexible. We now have better separation of concerns, which should also make the implementation more maintainable and easier for external contributors to understand.

TODO:

• squash

[tomholub]

Thank you - this looks to be an improvement 👍

[coveralls]

Pull Request Test Coverage Report for Build 501

• 568 of 809 (70.21%) changed or added relevant lines in 33 files are covered.
• 112 unchanged lines in 12 files lost coverage.
• Overall coverage increased (+0.3%) to 74.237%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pgpainless-core/src/main/java/org/pgpainless/signature/cleartext_signatures/MultiPassStrategy.java	0	1	0.0%
pgpainless-core/src/main/java/org/pgpainless/util/SignatureTree.java	0	1	0.0%
pgpainless-sop/src/main/java/org/pgpainless/sop/Print.java	5	6	83.33%
pgpainless-core/src/main/java/org/pgpainless/exception/KeyValidationException.java	0	2	0.0%
pgpainless-core/src/main/java/org/pgpainless/key/SubkeyIdentifier.java	2	4	50.0%
pgpainless-sop/src/main/java/org/pgpainless/sop/commands/Armor.java	0	2	0.0%
pgpainless-core/src/main/java/org/pgpainless/algorithm/negotiation/SymmetricKeyAlgorithmNegotiator.java	18	21	85.71%
pgpainless-sop/src/main/java/org/pgpainless/sop/SopKeyUtil.java	6	9	66.67%
pgpainless-core/src/main/java/org/pgpainless/encryption_signing/EncryptionResult.java	30	34	88.24%
pgpainless-core/src/main/java/org/pgpainless/key/info/KeyAccessor.java	19	23	82.61%

Files with Coverage Reduction	New Missed Lines	%
pgpainless-core/src/main/java/org/pgpainless/decryption_verification/OpenPgpMetadata.java	2	84.47%
pgpainless-core/src/main/java/org/pgpainless/encryption_signing/EncryptionBuilder.java	2	76.67%
pgpainless-core/src/main/java/org/pgpainless/key/SubkeyIdentifier.java	2	40.0%
pgpainless-core/src/main/java/org/pgpainless/util/Passphrase.java	2	90.2%
pgpainless-core/src/main/java/org/pgpainless/util/selection/key/impl/NoRevocation.java	2	40.0%
pgpainless-core/src/main/java/org/pgpainless/util/selection/key/impl/SignatureKeySelectionStrategy.java	2	83.33%
pgpainless-sop/src/main/java/org/pgpainless/sop/Print.java	3	50.0%
pgpainless-core/src/main/java/org/pgpainless/encryption_signing/EncryptionStream.java	4	83.58%
pgpainless-core/src/main/java/org/pgpainless/util/Tuple.java	6	0%
pgpainless-core/src/main/java/org/pgpainless/util/selection/key/impl/And.java	9	47.37%

Totals
Change from base Build 475:	0.3%
Covered Lines:	3674
Relevant Lines:	4949

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💛 - Coveralls