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

crypto/crypto.gyp

Index: crypto/crypto.gyp
===================================================================
--- crypto/crypto.gyp	(revision 201321)
+++ crypto/crypto.gyp	(working copy)
@@ -51,6 +51,7 @@
         }, {  # 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$'],
@@ -77,6 +78,7 @@
               '../third_party/openssl/openssl.gyp:openssl',
             ],
             'sources/': [
+              ['exclude', 'cup_nss\.cc$'],
               ['exclude', 'ec_private_key_nss\.cc$'],
               ['exclude', 'ec_signature_creator_nss\.cc$'],
               ['exclude', 'encryptor_nss\.cc$'],
@@ -137,6 +139,7 @@
             # 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',
@@ -159,6 +162,7 @@
             ],
           }, {
             'sources!': [
+              'cup_openssl.cc',
               'ec_private_key_openssl.cc',
               'ec_signature_creator_openssl.cc',
               'encryptor_openssl.cc',
@@ -186,6 +190,10 @@
         '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',
@@ -265,6 +273,7 @@
         'run_all_unittests.cc',
 
         # Tests.
+        'cup_unittest.cc',
         'curve25519_unittest.cc',
         'ec_private_key_unittest.cc',
         'ec_signature_creator_unittest.cc',