docs: add/update docs for osx dmg signing

doc/README_osx.txt

@@ -65,3 +65,18 @@ Background images and other features can be added to DMG files by inserting a
 .DS_Store before creation. The easiest way to create this file is to build a
 DMG without one, move it to a device running OSX, customize the layout, then
 grab the .DS_Store file for later use. That is the approach taken here.
+
+As of OSX Mavericks (10.9), using an Apple-blessed key to sign binaries is a
+requirement in order to satisfy the new Gatekeeper requirements. Because this
+private key cannot be shared, we'll have to be a bit creative in order for the
+build process to remain somewhat deterministic. Here's how it works:
+
+- Builders use gitian to create an unsigned release. This outputs an unsigned
+  dmg which users may choose to bless and run. It also outputs an unsigned app
+  structure in the form of a tarball, which also contains all of the tools
+  that have been previously (deterministically) built in order to create a
+  final dmg.
+- The Apple keyholder uses this unsigned app to create a detached signature,
+  using the script that is also included there.
+- Builders feed the unsigned app + detached signature back into gitian. It
+  uses the pre-built tools to recombine the pieces into a deterministic dmg.

doc/release-process.md

@@ -59,17 +59,18 @@ Release Process
 	./bin/gsign --signer $SIGNER --release ${VERSION}-win --destination ../gitian.sigs/ ../bitcoin/contrib/gitian-descriptors/gitian-win.yml
 	mv build/out/bitcoin-*.zip build/out/bitcoin-*.exe ../
 	./bin/gbuild --commit bitcoin=v${VERSION} ../bitcoin/contrib/gitian-descriptors/gitian-osx.yml
-	./bin/gsign --signer $SIGNER --release ${VERSION}-osx --destination ../gitian.sigs/ ../bitcoin/contrib/gitian-descriptors/gitian-osx.yml
+	./bin/gsign --signer $SIGNER --release ${VERSION}-osx-unsigned --destination ../gitian.sigs/ ../bitcoin/contrib/gitian-descriptors/gitian-osx.yml
+	mv build/out/bitcoin-*-unsigned.tar.gz inputs
 	mv build/out/bitcoin-*.tar.gz build/out/bitcoin-*.dmg ../
 	popd
-
+bitcoin-0.9.99-osx-unsigned.tar.gz
   Build output expected:
 
   1. source tarball (bitcoin-${VERSION}.tar.gz)
   2. linux 32-bit and 64-bit binaries dist tarballs (bitcoin-${VERSION}-linux[32|64].tar.gz)
   3. windows 32-bit and 64-bit installers and dist zips (bitcoin-${VERSION}-win[32|64]-setup.exe, bitcoin-${VERSION}-win[32|64].zip)
-  4. OSX installer (bitcoin-${VERSION}-osx.dmg)
+  4. OSX unsigned installer (bitcoin-${VERSION}-osx-unsigned.dmg)
-  5. Gitian signatures (in gitian.sigs/${VERSION}-<linux|win|osx>/(your gitian key)/
+  5. Gitian signatures (in gitian.sigs/${VERSION}-<linux|win|osx-unsigned>/(your gitian key)/
 
 ###Next steps:
 
@@ -78,7 +79,28 @@ Commit your signature to gitian.sigs:
 	pushd gitian.sigs
 	git add ${VERSION}-linux/${SIGNER}
 	git add ${VERSION}-win/${SIGNER}
-	git add ${VERSION}-osx/${SIGNER}
+	git add ${VERSION}-osx-unsigned/${SIGNER}
+	git commit -a
+	git push  # Assuming you can push to the gitian.sigs tree
+	popd
+
+Wait for OSX detached signature:
+	Once the OSX build has 3 matching signatures, Gavin will sign it with the apple App-Store key.
+	He will then upload a detached signature to be combined with the unsigned app to create a signed binary.
+
+Create the signed OSX binary:
+	pushd ./gitian-builder
+	# Fetch the signature as instructed by Gavin
+	cp signature.tar.gz inputs/
+	./bin/gbuild -i ../bitcoin/contrib/gitian-descriptors/gitian-osx-signer.yml
+	./bin/gsign --signer $SIGNER --release ${VERSION}-osx-signed --destination ../gitian.sigs/ ../bitcoin/contrib/gitian-descriptors/gitian-osx-signer.yml
+	mv build/out/bitcoin-${VERSION}-osx.dmg ../
+	popd
+
+Commit your signature for the signed OSX binary:
+
+	pushd gitian.sigs
+	git add ${VERSION}-osx-signed/${SIGNER}
 	git commit -a
 	git push  # Assuming you can push to the gitian.sigs tree
 	popd
@@ -91,8 +113,6 @@ Commit your signature to gitian.sigs:
 
     - Code-sign Windows -setup.exe (in a Windows virtual machine using signtool)
 
-    - Code-sign MacOSX .dmg
-
   Note: only Gavin has the code-signing keys currently.
 
 - Create `SHA256SUMS.asc` for the builds, and GPG-sign it: