api: use signed endpoint

Library/Homebrew/api.rb

@@ -56,7 +56,7 @@ module Homebrew
                       (Homebrew::EnvConfig.no_auto_update? ||
                       ((Time.now - Homebrew::EnvConfig.api_auto_update_secs.to_i) < target.mtime))
 
-      begin
+      json_data = begin
         begin
           args = curl_args.dup
           args.prepend("--time-cond", target.to_s) if target.exist? && !target.empty?
@@ -83,7 +83,7 @@ module Homebrew
         end
 
         FileUtils.touch(target) unless skip_download
-        [JSON.parse(target.read), !skip_download]
+        JSON.parse(target.read)
       rescue JSON::ParserError
         target.unlink
         retry_count += 1
@@ -92,6 +92,21 @@ module Homebrew
 
         retry
       end
+
+      if endpoint.end_with?(".jws.json")
+        success, data = verify_and_parse_jws(json_data)
+        unless success
+          target.unlink
+          odie <<~EOS
+            Failed to verify integrity (#{data}) of:
+              #{url}
+            Potential MITM attempt detected. Please run `brew update` and try again.
+          EOS
+        end
+        [data, !skip_download]
+      else
+        [json_data, !skip_download]
+      end
     end
 
     sig { params(name: String, git_head: T.nilable(String)).returns(String) }
@@ -140,5 +155,31 @@ module Homebrew
 
       false
     end
+
+    sig { params(json_data: Hash).returns([T::Boolean, T.any(String, Array, Hash)]) }
+    private_class_method def self.verify_and_parse_jws(json_data)
+      signatures = json_data["signatures"]
+      homebrew_signature = signatures&.find { |sig| sig.dig("header", "kid") == "homebrew-1" }
+      return false, "key not found" if homebrew_signature.nil?
+
+      header = JSON.parse(Base64.urlsafe_decode64(homebrew_signature["protected"]))
+      if header["alg"] != "PS512" || header["b64"] != false # NOTE: nil has a meaning of true
+        return false, "invalid algorithm"
+      end
+
+      require "openssl"
+
+      pubkey = OpenSSL::PKey::RSA.new((HOMEBREW_LIBRARY_PATH/"api/homebrew-1.pem").read)
+      signing_input = "#{homebrew_signature["protected"]}.#{json_data["payload"]}"
+      unless pubkey.verify_pss("SHA512",
+                               Base64.urlsafe_decode64(homebrew_signature["signature"]),
+                               signing_input,
+                               salt_length: :digest,
+                               mgf1_hash:   "SHA512")
+        return false, "signature mismatch"
+      end
+
+      [true, JSON.parse(json_data["payload"])]
+    end
   end
 end

Library/Homebrew/api/cask.rb

@@ -27,8 +27,8 @@ module Homebrew
 
         sig { returns(T::Boolean) }
         def download_and_cache_data!
-          json_casks, updated = Homebrew::API.fetch_json_api_file "cask.json",
+          json_casks, updated = Homebrew::API.fetch_json_api_file "cask.jws.json",
-                                                                  target: HOMEBREW_CACHE_API/"cask.json"
+                                                                  target: HOMEBREW_CACHE_API/"cask.jws.json"
 
           cache["casks"] = json_casks.to_h do |json_cask|
             [json_cask["token"], json_cask.except("token")]

Library/Homebrew/api/formula.rb

@@ -22,8 +22,8 @@ module Homebrew
 
         sig { returns(T::Boolean) }
         def download_and_cache_data!
-          json_formulae, updated = Homebrew::API.fetch_json_api_file "formula.json",
+          json_formulae, updated = Homebrew::API.fetch_json_api_file "formula.jws.json",
-                                                                     target: HOMEBREW_CACHE_API/"formula.json"
+                                                                     target: HOMEBREW_CACHE_API/"formula.jws.json"
 
           cache["aliases"] = {}
           cache["formulae"] = json_formulae.to_h do |json_formula|

Library/Homebrew/api/homebrew-1.pem

@@ -0,0 +1,14 @@
+-----BEGIN PUBLIC KEY-----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+-----END PUBLIC KEY-----

Library/Homebrew/cmd/update.sh

@@ -766,28 +766,28 @@ EOS
 
     for formula_or_cask in formula cask
     do
-      if [[ -f "${HOMEBREW_CACHE}/api/${formula_or_cask}.json" ]]
+      if [[ -f "${HOMEBREW_CACHE}/api/${formula_or_cask}.jws.json" ]]
       then
-        INITIAL_JSON_BYTESIZE="$(wc -c "${HOMEBREW_CACHE}"/api/"${formula_or_cask}".json)"
+        INITIAL_JSON_BYTESIZE="$(wc -c "${HOMEBREW_CACHE}"/api/"${formula_or_cask}".jws.json)"
       fi
       JSON_URLS=()
       if [[ -n "${HOMEBREW_API_DOMAIN}" && "${HOMEBREW_API_DOMAIN}" != "${HOMEBREW_API_DEFAULT_DOMAIN}" ]]
       then
-        JSON_URLS=("${HOMEBREW_API_DOMAIN}/${formula_or_cask}.json")
+        JSON_URLS=("${HOMEBREW_API_DOMAIN}/${formula_or_cask}.jws.json")
       fi
-      JSON_URLS+=("${HOMEBREW_API_DEFAULT_DOMAIN}/${formula_or_cask}.json")
+      JSON_URLS+=("${HOMEBREW_API_DEFAULT_DOMAIN}/${formula_or_cask}.jws.json")
       for json_url in "${JSON_URLS[@]}"
       do
         time_cond=()
-        if [[ -s "${HOMEBREW_CACHE}/api/${formula_or_cask}.json" ]]
+        if [[ -s "${HOMEBREW_CACHE}/api/${formula_or_cask}.jws.json" ]]
         then
-          time_cond=("--time-cond" "${HOMEBREW_CACHE}/api/${formula_or_cask}.json")
+          time_cond=("--time-cond" "${HOMEBREW_CACHE}/api/${formula_or_cask}.jws.json")
         fi
         curl \
           "${CURL_DISABLE_CURLRC_ARGS[@]}" \
           --fail --compressed --silent \
           --speed-limit "${HOMEBREW_CURL_SPEED_LIMIT}" --speed-time "${HOMEBREW_CURL_SPEED_TIME}" \
-          --location --remote-time --output "${HOMEBREW_CACHE}/api/${formula_or_cask}.json" \
+          --location --remote-time --output "${HOMEBREW_CACHE}/api/${formula_or_cask}.jws.json" \
           "${time_cond[@]}" \
           --user-agent "${HOMEBREW_USER_AGENT_CURL}" \
           "${json_url}"
@@ -796,8 +796,8 @@ EOS
       done
       if [[ ${curl_exit_code} -eq 0 ]]
       then
-        touch "${HOMEBREW_CACHE}/api/${formula_or_cask}.json"
+        touch "${HOMEBREW_CACHE}/api/${formula_or_cask}.jws.json"
-        CURRENT_JSON_BYTESIZE="$(wc -c "${HOMEBREW_CACHE}"/api/"${formula_or_cask}".json)"
+        CURRENT_JSON_BYTESIZE="$(wc -c "${HOMEBREW_CACHE}"/api/"${formula_or_cask}".jws.json)"
         if [[ "${INITIAL_JSON_BYTESIZE}" != "${CURRENT_JSON_BYTESIZE}" ]]
         then
           rm -f "${HOMEBREW_CACHE}/api/${formula_or_cask}_names.txt"

Library/Homebrew/test/api/cask_spec.rb

@@ -9,12 +9,16 @@ describe Homebrew::API::Cask do
   before do
     stub_const("Homebrew::API::HOMEBREW_CACHE_API", cache_dir)
     Homebrew::API.clear_cache
+    described_class.clear_cache
   end
 
   def mock_curl_download(stdout:)
     allow(Utils::Curl).to receive(:curl_download) do |*_args, **kwargs|
       kwargs[:to].write stdout
     end
+    allow(Homebrew::API).to receive(:verify_and_parse_jws) do |json_data|
+      [true, json_data]
+    end
   end
 
   describe "::all_casks" do

Library/Homebrew/test/api/formula_spec.rb

@@ -8,12 +8,16 @@ describe Homebrew::API::Formula do
 
   before do
     stub_const("Homebrew::API::HOMEBREW_CACHE_API", cache_dir)
+    described_class.clear_cache
   end
 
   def mock_curl_download(stdout:)
     allow(Utils::Curl).to receive(:curl_download) do |*_args, **kwargs|
       kwargs[:to].write stdout
     end
+    allow(Homebrew::API).to receive(:verify_and_parse_jws) do |json_data|
+      [true, json_data]
+    end
   end
 
   describe "::all_formulae" do