Expand CRX verifier to verify CRX₃ files.

components/crx_file/crx3.proto

Index: components/crx_file/crx3.proto
diff --git a/components/crx_file/crx3.proto b/components/crx_file/crx3.proto
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+++ b/components/crx_file/crx3.proto
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+// Copyright (c) 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+
+package crx_file;
+
+// A CRX₃ file is a binary file of the following format:
+// [4 octets]: "Cr24", a magic number.
+// [4 octets]: The version of the *.crx file format used (currently 3).
+// [4 octets]: N, little-endian, the length of the header section.
+// [N octets]: The header (the binary encoding of a CrxFileHeader).
+// [M octets]: The ZIP archive.
+// Clients should reject CRX₃ files that contain an N that is too large for the
+// client to safely handle in memory.
+
+message CrxFileHeader {
+  // PSS signature with RSA public key. The public key is formatted as a
+  // X.509 SubjectPublicKeyInfo block, as in CRX₂. In the common case of a
+  // developer key proof, the first 128 bits of the SHA-256 hash of the
+  // public key must equal the crx_id.
+  repeated AsymmetricKeyProof sha256_with_rsa = 2;
+
+  // ECDSA signature, using the NIST P-256 curve. Public key appears in
+  // named-curve format.
+  // The pinned algorithm will be this, at least on 2017-01-01.
+  repeated AsymmetricKeyProof sha256_with_ecdsa = 3;
+
+  // The binary form of a SignedData message. We do not use a nested
+  // SignedData message, as handlers of this message must verify the proofs
+  // on exactly these bytes, so it is convenient to parse in two steps.
+  //
+  // All proofs in this CrxFile message are on the value
+  // "CRX3 SignedData\x00" + signed_header_size + signed_header_data +
+  // archive, where "\x00" indicates an octet with value 0, "CRX3 SignedData"
+  // is encoded using UTF-8, signed_header_size is the size in octets of the
+  // contents of this field and is encoded using 4 octets in little-endian
+  // order, signed_header_data is exactly the content of this field, and
+  // archive is the remaining contents of the file following the header.
+  optional bytes signed_header_data = 10000;
+}
+
+message AsymmetricKeyProof {
+  optional bytes public_key = 1;
+  optional bytes signature = 2;
+}
+
+message SignedData {
+  // This is simple binary, not UTF-8 encoded mpdecimal; i.e. it is exactly
+  // 16 bytes long.
+  optional bytes crx_id = 1;
+}