diff --git a/dependabot-core.gemspec b/dependabot-core.gemspec
index 6b96026832..936f22c725 100644
--- a/dependabot-core.gemspec
+++ b/dependabot-core.gemspec
@@ -25,12 +25,12 @@ Gem::Specification.new do |spec|
   spec.add_dependency "docker_registry2", "~> 1.3", ">= 1.3.3"
   spec.add_dependency "excon", "~> 0.55"
   spec.add_dependency "gitlab", "~> 4.1"
+  spec.add_dependency "gpgme", "~> 2.0"
   spec.add_dependency "nokogiri", "~> 1.8"
   spec.add_dependency "octokit", "~> 4.6"
   spec.add_dependency "parseconfig", "~> 1.0"
   spec.add_dependency "parser", "~> 2.5"
   spec.add_dependency "toml-rb", "~> 1.1"
-  spec.add_dependency "gpgme", "~> 2.0"
 
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec", "~> 3.7.0"
diff --git a/lib/dependabot/pull_request_creator.rb b/lib/dependabot/pull_request_creator.rb
index 99de3595da..f1c5498e41 100644
--- a/lib/dependabot/pull_request_creator.rb
+++ b/lib/dependabot/pull_request_creator.rb
@@ -10,11 +10,11 @@ class PullRequestCreator
 
     attr_reader :repo_name, :dependencies, :files, :base_commit,
                 :github_client, :pr_message_footer, :target_branch,
-                :author_details, :custom_labels
+                :author_details, :signature_key, :custom_labels
 
     def initialize(repo:, base_commit:, dependencies:, files:, github_client:,
                    pr_message_footer: nil, target_branch: nil,
-                   author_details: nil, custom_labels: nil)
+                   custom_labels: nil, author_details: nil, signature_key: nil)
       @dependencies      = dependencies
       @repo_name         = repo
       @base_commit       = base_commit
@@ -23,6 +23,7 @@ def initialize(repo:, base_commit:, dependencies:, files:, github_client:,
       @pr_message_footer = pr_message_footer
       @target_branch     = target_branch
       @author_details    = author_details
+      @signature_key     = signature_key
       @custom_labels     = custom_labels
 
       check_dependencies_have_previous_version
@@ -48,6 +49,7 @@ def create
         pr_description: message_builder.pr_message,
         pr_name: message_builder.pr_name,
         author_details: author_details,
+        signature_key: signature_key,
         custom_labels: custom_labels
       ).create
     end
diff --git a/lib/dependabot/pull_request_creator/github.rb b/lib/dependabot/pull_request_creator/github.rb
index 699752a261..f80ad297bf 100644
--- a/lib/dependabot/pull_request_creator/github.rb
+++ b/lib/dependabot/pull_request_creator/github.rb
@@ -61,6 +61,7 @@ def create_commit
         options = author_details&.any? ? { author: author_details } : {}
 
         if options[:author]&.any? && signature_key
+          timestamp = Time.now.utc
           options[:signature] = commit_signature(tree, timestamp)
           options[:author][:date] = timestamp.iso8601
         end
@@ -171,7 +172,8 @@ def default_branch
 
       def commit_signature(tree, timestamp)
         time_str = timestamp.strftime("%s %z")
-        name, email = author_details[:name], author_details[:email]
+        name = author_details[:name]
+        email = author_details[:email]
         commit_object = [
           "commit #{commit_message.length}\0tree #{tree.sha}",
           "parent #{base_commit}",
diff --git a/lib/dependabot/pull_request_updater.rb b/lib/dependabot/pull_request_updater.rb
index 219d31c48e..53df438864 100644
--- a/lib/dependabot/pull_request_updater.rb
+++ b/lib/dependabot/pull_request_updater.rb
@@ -5,16 +5,18 @@
 module Dependabot
   class PullRequestUpdater
     attr_reader :watched_repo, :files, :base_commit, :github_client,
-                :pull_request_number, :author_details
+                :pull_request_number, :author_details, :signature_key
 
     def initialize(repo:, base_commit:, files:, github_client:,
-                   pull_request_number:, author_details: nil)
+                   pull_request_number:, author_details: nil,
+                   signature_key: nil)
       @watched_repo = repo
       @base_commit = base_commit
       @files = files
       @github_client = github_client
       @pull_request_number = pull_request_number
       @author_details = author_details
+      @signature_key = signature_key
     end
 
     def update
@@ -41,6 +43,13 @@ def create_commit
       tree = create_tree
 
       options = author_details&.any? ? { author: author_details } : {}
+
+      if options[:author]&.any? && signature_key
+        timestamp = Time.now.utc
+        options[:signature] = commit_signature(tree, timestamp)
+        options[:author][:date] = timestamp.iso8601
+      end
+
       github_client.create_commit(
         watched_repo,
         commit_message,
@@ -87,15 +96,39 @@ def update_branch(commit)
       )
     rescue Octokit::UnprocessableEntity => error
       # Return quietly if the branch has been deleted
-      return nil if error.message.match?(/Reference does not exist/)
+      return nil if error.message.match?(/Reference does not exist/i)
 
       # Return quietly if the branch has been merged
-      return nil if error.message.match?(/Reference cannot be updated/)
+      return nil if error.message.match?(/Reference cannot be updated/i)
       raise
     end
 
     def commit_message
       github_client.git_commit(watched_repo, pull_request.head.sha).message
     end
+
+    def commit_signature(tree, timestamp)
+      time_str = timestamp.strftime("%s %z")
+      name = author_details[:name]
+      email = author_details[:email]
+      commit_object = [
+        "commit #{commit_message.length}\0tree #{tree.sha}",
+        "parent #{base_commit}",
+        "author #{name} <#{email}> #{time_str}",
+        "committer #{name} <#{email}> #{time_str}",
+        "",
+        commit_message
+      ]
+      data = commit_object.join("\n")
+
+      Dir.mktmpdir do |dir|
+        GPGME::Engine.home_dir = dir
+        GPGME::Key.import(signature_key)
+
+        crypto = GPGME::Crypto.new(armor: true)
+        opts = { mode: GPGME::SIG_MODE_DETACH, signer: email }
+        return crypto.sign(data, opts)
+      end
+    end
   end
 end