Per discussion, implement the Omaha Client Update Protocol (CUP) in src/crypto.

crypto/crypto.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,
     # Put all transitive dependencies for Windows HMAC here.
     # This is required so that we can build them for nacl win64.
     'hmac_win64_related_sources': [
@@ skipping 33 matching lines @@
           ],
           'conditions': [
             [ 'chromeos==1', {
                 'sources/': [ ['include', '_chromeos\\.cc$'] ]
               },
             ],
           ],
         }, {  # os_posix != 1 or OS == "mac" or OS == "ios" or OS == "android"
             'sources/': [
               ['exclude', '_nss\.cc$'],
+              ['include', 'cup_nss\.cc$'],
               ['include', 'ec_private_key_nss\.cc$'],
               ['include', 'ec_signature_creator_nss\.cc$'],
               ['include', 'encryptor_nss\.cc$'],
               ['include', 'hmac_nss\.cc$'],
               ['include', 'signature_verifier_nss\.cc$'],
               ['include', 'symmetric_key_nss\.cc$'],
             ],
             'sources!': [
               'hmac_win.cc',
               'openpgp_symmetric_encryption.cc',
               'openpgp_symmetric_encryption.h',
               'symmetric_key_win.cc',
             ],
         }],
         [ 'OS != "mac" and OS != "ios"', {
           'sources!': [
             'apple_keychain.h',
             'mock_apple_keychain.cc',
             'mock_apple_keychain.h',
           ],
         }],
         [ 'OS == "android"', {
             'dependencies': [
               '../third_party/openssl/openssl.gyp:openssl',
             ],
             'sources/': [
+              ['exclude', 'cup_nss\.cc$'],
               ['exclude', 'ec_private_key_nss\.cc$'],
               ['exclude', 'ec_signature_creator_nss\.cc$'],
               ['exclude', 'encryptor_nss\.cc$'],
               ['exclude', 'hmac_nss\.cc$'],
               ['exclude', 'signature_verifier_nss\.cc$'],
               ['exclude', 'symmetric_key_nss\.cc$'],
             ],
         }],
         [ 'os_bsd==1', {
           'link_settings': {
@@ skipping 40 matching lines @@
           ],
         }],
         [ 'OS == "win"', {
           # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
           'msvs_disabled_warnings': [4267, ],
         }],
         [ 'use_openssl==1', {
             # TODO(joth): Use a glob to match exclude patterns once the
             #             OpenSSL file set is complete.
             'sources!': [
+              'cup_nss.cc',
               'ec_private_key_nss.cc',
               'ec_signature_creator_nss.cc',
               'encryptor_nss.cc',
               'hmac_nss.cc',
               'nss_util.cc',
               'nss_util.h',
               'openpgp_symmetric_encryption.cc',
               'rsa_private_key_nss.cc',
               'secure_hash_default.cc',
               'signature_creator_nss.cc',
               'signature_verifier_nss.cc',
               'symmetric_key_nss.cc',
               'third_party/nss/chromium-blapi.h',
               'third_party/nss/chromium-blapit.h',
               'third_party/nss/chromium-nss.h',
               'third_party/nss/chromium-sha256.h',
               'third_party/nss/pk11akey.cc',
               'third_party/nss/secsign.cc',
               'third_party/nss/sha512.cc',
             ],
           }, {
             'sources!': [
+              'cup_openssl.cc',
               'ec_private_key_openssl.cc',
               'ec_signature_creator_openssl.cc',
               'encryptor_openssl.cc',
               'hmac_openssl.cc',
               'openssl_util.cc',
               'openssl_util.h',
               'rsa_private_key_openssl.cc',
               'secure_hash_openssl.cc',
               'signature_creator_openssl.cc',
               'signature_verifier_openssl.cc',
               'symmetric_key_openssl.cc',
             ],
         },],
       ],
       'sources': [
         # NOTE: all transitive dependencies of HMAC on windows need
         #     to be placed in the source list above.
         '<@(hmac_win64_related_sources)',
         'apple_keychain.h',
         'apple_keychain_ios.mm',
         'apple_keychain_mac.mm',
         'capi_util.cc',
         'capi_util.h',
         'crypto_export.h',
         'crypto_module_blocking_password_delegate.h',
         'cssm_init.cc',
         'cssm_init.h',
+        'cup.cc',
+        'cup.h',
+        'cup_nss.cc',
+        'cup_openssl.cc',
         'curve25519.cc',
         'curve25519.h',
         'curve25519-donna.c',
         'ghash.cc',
         'ghash.h',
         'ec_private_key.h',
         'ec_private_key_nss.cc',
         'ec_private_key_openssl.cc',
         'ec_signature_creator.cc',
         'ec_signature_creator.h',
@@ skipping 59 matching lines @@
       ],
     },
     {
       'target_name': 'crypto_unittests',
       'type': 'executable',
       'sources': [
         # Infrastructure files.
         'run_all_unittests.cc',
 
         # Tests.
+        'cup_unittest.cc',
         'curve25519_unittest.cc',
         'ec_private_key_unittest.cc',
         'ec_signature_creator_unittest.cc',
         'encryptor_unittest.cc',
         'ghash_unittest.cc',
         'hkdf_unittest.cc',
         'hmac_unittest.cc',
         'nss_util_unittest.cc',
         'p224_unittest.cc',
         'p224_spake_unittest.cc',
@@ skipping 92 matching lines @@
           'configurations': {
             'Common_Base': {
               'msvs_target_platform': 'x64',
             },
           },
         },
       ],
     }],
   ],
 }