Linzer

Linzer is a Ruby library for HTTP Message Signatures (RFC 9421).

Install

Add the following line to your Gemfile:

gem "linzer"

Or just gem install linzer.

Usage

TL;DR: I just want to protect my application!!

Add the following middleware to your Rack application and configure it as needed, e.g.:

# config.ru
use Rack::Auth::Signature, except: "/login",
  default_key: {material: Base64.strict_decode64(ENV["MYAPP_KEY"]), alg: "hmac-sha256"}
  # or: default_key: {material: IO.read("app/config/pubkey.pem"), "ed25519"}

or on more complex scenarios:

# config.ru
use Rack::Auth::Signature, except: "/login",
  config_path: "app/configuration/http-signatures.yml"

or with a typical Rails application:

# config/application.rb
config.middleware.use Rack::Auth::Signature, except: "/login",
  config_path: "http-signatures.yml"

And that's it, all routes in the example app (except /login) above will require a valid signature created with the respective private key held by a client. For more details on what configuration options are available, take a look at examples/sinatra/http-signatures.yml to get started and/or lib/rack/auth/signature.rb for full implementation details.

To learn about more specific scenarios or use cases, keep reading on below.

To sign a HTTP request:

There are several options:

If you are using http gem:

# first require http signatures feature class ready to be used with http gem:
require "linzer/http/signature_feature"

key = Linzer.generate_ed25519_key # generate a new key pair
# => #<Linzer::Ed25519::Key:0x00000fe13e9bd208
# or load an existing key with:
# key = Linzer.new_ed25519_key(IO.read("key"), "mykeyid")

# then send the request:
url = "https://example.org/api"
response = HTTP.headers(date: Time.now.to_s, foo: "bar")
               .use(http_signature: {key: key} # <--- covered components
               .get(url) # and signature params can also be customized on the client
=> #<HTTP::Response/1.1 200 OK {"Content-Type" => ...
response.body.to_s
=> "protected content..."

If you are using plain old Net::HTTP:

key = Linzer.generate_ed25519_key
# => #<Linzer::Ed25519::Key:0x00000fe13e9bd208

uri = URI("https://example.org/api/task")
request = Net::HTTP::Get.new(uri)
request["date"] = Time.now.to_s

Linzer.sign!(
  request,
  key: key,
  components: %w[@method @request-target date],
  label: "sig1",
  params: {
    created: Time.now.to_i
  }
)

request["signature"]
# => "sig1=:Cv1TUCxUpX+5SVa7pH0Xh..."
request["signature-input"]
# => "sig1=(\"@method\" \"@request-target\" \"date\" ..."}

Then you can submit the signed request with Net::HTTP client:

require "net/http"

http = Net::HTTP.new(uri.host, uri.port)
http.set_debug_output($stderr)
response = http.request(request)
# opening connection to localhost:9292...
# opened
# <- "POST /some_uri HTTP/1.1\r\n
# <- Date: Fri, 23 Feb 2024 17:57:23 GMT\r\n
# <- X-Custom-Header: foo\r\n
# <- Signature: sig1=:Cv1TUCxUpX+5SVa7pH0X...
# <- Signature-Input: sig1=(\"date\" \"x-custom-header\" \"@method\"...
# <- Accept-Encoding: gzip;q=1.0,deflate;q=0.6,identity;q=0.3\r\n
# <- Accept: */*\r\n
# <- User-Agent: Ruby\r\n
# <- Connection: close\r\n
# <- Host: localhost:9292
# <- Content-Length: 4\r\n
# <- Content-Type: application/x-www-form-urlencoded\r\n\r\n"
# <- "data"
#
# -> "HTTP/1.1 200 OK\r\n"
# -> "Content-Type: text/html;charset=utf-8\r\n"
# -> "Content-Length: 0\r\n"
# -> "X-Xss-Protection: 1; mode=block\r\n"
# -> "X-Content-Type-Options: nosniff\r\n"
# -> "X-Frame-Options: SAMEORIGIN\r\n"
# -> "Server: WEBrick/1.8.1 (Ruby/3.2.0/2022-12-25)\r\n"
# -> "Date: Thu, 28 Mar 2024 17:19:21 GMT\r\n"
# -> "Connection: close\r\n"
# -> "\r\n"
# reading 0 bytes...
# -> ""
# read 0 bytes
# Conn close
# => #<Net::HTTPOK 200 OK readbody=true>

Or you can also use the simple HTTP client bundled with this library:

(This client is probably not suitable for production use but could be useful enough to get started. It's build on top of Net::HTTP.)

key = Linzer.generate_rsa_pss_sha512_key(4096)
uri = URI("https://example.org/api/task")
headers = {"date" => Time.now.to_s}
response =
  Linzer::HTTP
    .post("http://httpbin.org/headers",
          data: "foo",
          debug: true,
          key: key,
          headers: headers)
...
=> #<Net::HTTPOK 200 OK readbody=true>

To verify an incoming request on the server side:

The middleware Rack::Auth::Signature can be used for this scenario as shown above.

Or directly in the application controller (or routes), the incoming request can be verified with the following approach:

post "/foo" do
  request
  # =>
  # #<Sinatra::Request:0x000000011e5a5d60
  #  @env=
  #   {"GATEWAY_INTERFACE" => "CGI/1.1",
  #   "PATH_INFO" => "/api",
  # ...

  result = Linzer.verify!(request, key: some_client_key)
  # => true
  ...
end

If the signature is missing or invalid, the verification method will raise an exception with a message clarifying why the request signature failed verification.

Also, for additional flexibility on the server side, the method above can take a block with the keyid parameter extracted from the signature (if any) as argument. This can be useful to retrieve key data from databases/caches on the server side, e.g.:

get "/bar" do
  ...
  result = Linzer.verify!(request) do |keyid|
    retrieve_pubkey_from_db(db_client, keyid)
  end
  # => true
  ...
end

To verify a received response on the client side:

It's similar to verifying requests, the same method is used, see example below:

response
# => #<Net::HTTPOK 200 OK readbody=true>
response.body
# => "protected"
pubkey = Linzer.new_ed25519_key(IO.read("pubkey.pem"))
result = Linzer.verify!(response, key: pubkey, no_older_than: 600)
# => true

To sign an outgoing response on the server side:

Again, the same principle used to sign outgoing requests, the same method is used, see example below:

put "/baz" do
  ...
  response
  # => #<Sinatra::Response:0x0000000109ac40b8 ...
  response.headers["x-custom-app-header"] = "..."
  Linzer.sign!(response,
    key: my_key,
    components: %w[@status content-type content-digest x-custom-app-header],
    label: "sig1",
    params: {
      created: Time.now.to_i
    }
  )
  response["signature"]
  # => "sig1=:2TPCzD4l48bg6LMcVXdV9u..."
  response["signature-input"]
  # => "sig1=(\"@status\" \"content-type\" \"content-digest\"..."
  ...
end

What do you do if you want to sign/verify requests and responses with your preferred HTTP ruby library/framework (not using Rack or Net::HTTP, for example)?

You can provide an adapter class and then register it with this library. For guidance on how to implement such adapters, you can consult an example adapter for http gem response included with this gem or the ones provided out of the box.

For how to register a custom adapter and how to verify signatures in a response, see this example:

Linzer::Message.register_adapter(HTTP::Response, Linzer::Message::Adapter::HTTPGem::Response)
# Linzer::Message.register_adapter(HTTP::Response, MyOwnResponseAdapter) # or use your own adapter
response = HTTP.get("http://www.example.com/api/service/task")
# => #<HTTP::Response/1.1 200 OK ...
response["signature"]
=> "sig1=:oqzDlQmfejfT..."
response["signature-input"]
=> "sig1=(\"@status\" \"foo\");created=1746480237"
result = Linzer.verify!(response, key: my_key)
# => true

---

Furthermore, on some low-level scenarios where a user wants or needs additional control on how the signing and verification routines are performed, Linzer allows to manipulate instances of internal HTTP messages (requests & responses, see Linzer::Message class and available adapters), signature objects (Linzer::Signature) and how to register additional message adapters for any HTTP ruby library not supported out of the box by this gem.

See below for a few examples of these scenarios.

To verify a valid signature:

test_ed25519_key_pub = key.material.public_to_pem
# => "-----BEGIN PUBLIC KEY-----\nMCowBQYDK2VwAyEAK1ZrC4JqC356pRsUiLVJdFZ3dAjo909VfWs1li33MCQ=\n-----END PUBLIC KEY-----\n"

pubkey = Linzer.new_ed25519_public_key(test_ed25519_key_pub, "some-key-ed25519")
# => #<Linzer::Ed25519::Key:0x00000fe19b9384b0

message = Linzer::Message.new(request)

signature = Linzer::Signature.build(message.headers)

Linzer.verify(pubkey, message, signature)
# => true

To mitigate the risk of "replay attacks" (i.e. an attacker capturing a message with a valid signature and re-sending it at a later point) applications may want to validate the created parameter of the signature. Linzer can do this automatically when given the optional no_older_than keyword argument:

Linzer.verify(