Fix code and add a test case. The old code passed on the original input
stream, which has already been consumed.

Bug: 570501
Change-Id: I81f60698ce42443df57e59b1d1ab155574136fa8
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Add detection for the key-value pair format that was available in
gpg-agent for some time already and that has become the default since
gpg-agent 2.2.20. If a secret key in the .gnupg/private-keys-v1.d
directory is found to have this format, extract the human-readable key
from it, convert it to the binary serialized form and hand that to
BouncyCastle.

Encrypted keys in the new format may use AES/OCB. OCB is a patent-
encumbered algorithm; although there is a license for open-source
software, that may not be good enough and OCB may not be available in
Java. It is not available in the default security provider in Java,
and it is also not available in the BouncyCastle version included in
Eclipse.

Implement AES/OCB decryption, throwing a PGPException with a nice
message if the algorithm is not available. Include a copy of the normal
s-expression parser of BouncyCastle and fix it to properly handle data
from such keys: such keys do not contain an internal hash since the
AES/OCB cipher includes and checks a MAC already.

Bug: 570501
Change-Id: Ifa6391a809a84cfc6ae7c6610af6a79204b4143b
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

The gpg-agent stores secret keys in individual files in the secret
key directory private-keys-v1.d. The files have the key's keygrip
(in upper case) as name and extension ".key".

A keygrip is a SHA1 hash over the parameters of the public key. By
computing this keygrip, we can pre-compute the expected file name and
then check only that one file instead of having to iterate over all
keys stored in that directory.

This file naming scheme is actually an implementation detail of
gpg-agent. It is unlikely to change, though. The keygrip itself is
computed via libgcrypt and will remain stable according to the GPG
main author.[1]

Add an implementation for calculating the keygrip and include tests.
Do not iterate over files in BouncyCastleGpgKeyLocator but only check
the single file identified by the keygrip.

Ideally upstream BouncyCastle would provide such a getKeyGrip() method.
But as it re-builds GPG and libgcrypt internals, it's doubtful it would
be included there, and since BouncyCastle even lacks a number of curve
OIDs for ed25519/curve25519 and uses the short-Weierstrass parameters
instead of the more common Montgomery parameters, including it there
might be quite a bit of work.

[1] http://gnupg.10057.n7.nabble.com/GnuPG-2-1-x-and-2-2-x-keyring-formats-tp54146p54154.html

Bug: 547536
Change-Id: I30022a0e7b33b1bf35aec1222f84591f0c30ddfd
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Although not mentioned in the GPG documentation at [1], GPG uses
case-insensitive matching also for the '<' (exact e-mail) and '@'
(partial e-mail) operators. Matching for '=' (full exact match) is
case-sensitive. Compare [2].

[1] https://www.gnupg.org/documentation/manuals/gnupg/Specify-a-User-ID.html
[2] https://dev.gnupg.org/source/gnupg/browse/master/g10/keyring.c;22f7dddc34446a8c3e9eddf6cb281f16802351d7$890

Bug: 547789
Change-Id: I2f5ab65807d5dde3aa00ff032894701bbd8418c9
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Motivation: BouncyCastle serves as 'default' implementation of
the GPG Signer. If a client application does not use it there is no need
to pull in this dependency, especially since BouncyCastle is a large
library.

Move the classes depending on BouncyCastle to an OSGi fragment extending
the org.eclipse.jgit bundle. They are moved to a distinct internal
package in order to avoid split packages. This doesn't break public API
since these classes were already in an internal package before this
change.

Add a new feature org.eclipse.jgit.gpg.bc to enable installation. With
that users can now decide if they want to install it.

Attempts to sign a commit if org.eclipse.jgit.gpg.bc isn't available
will result in ServiceUnavailableException being thrown.

Bug: 559106
Change-Id: I42fd6c00002e17aa9a7be96ae434b538ea86ccf8
Also-by: Michael Dardis <git@md-5.net>
Signed-off-by: Michael Dardis <git@md-5.net>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
Signed-off-by: David Ostrovsky <david@ostrovsky.org>