app/controllers/concerns/signature_verification.rb
# frozen_string_literal: true
# Implemented according to HTTP signatures (Draft 6)
# <https://tools.ietf.org/html/draft-cavage-http-signatures-06>
module SignatureVerification
extend ActiveSupport::Concern
include DomainControlHelper
EXPIRATION_WINDOW_LIMIT = 12.hours
CLOCK_SKEW_MARGIN = 1.hour
class SignatureVerificationError < StandardError; end
class SignatureParamsParser < Parslet::Parser
rule(:token) { match("[0-9a-zA-Z!#$%&'*+.^_`|~-]").repeat(1).as(:token) }
rule(:quoted_string) { str('"') >> (qdtext | quoted_pair).repeat.as(:quoted_string) >> str('"') }
# qdtext and quoted_pair are not exactly according to spec but meh
rule(:qdtext) { match('[^\\\\"]') }
rule(:quoted_pair) { str('\\') >> any }
rule(:bws) { match('\s').repeat }
rule(:param) { (token.as(:key) >> bws >> str('=') >> bws >> (token | quoted_string).as(:value)).as(:param) }
rule(:comma) { bws >> str(',') >> bws }
# Old versions of node-http-signature add an incorrect "Signature " prefix to the header
rule(:buggy_prefix) { str('Signature ') }
rule(:params) { buggy_prefix.maybe >> (param >> (comma >> param).repeat).as(:params) }
root(:params)
end
class SignatureParamsTransformer < Parslet::Transform
rule(params: subtree(:p)) do
(p.is_a?(Array) ? p : [p]).each_with_object({}) { |(key, val), h| h[key] = val }
end
rule(param: { key: simple(:key), value: simple(:val) }) do
[key, val]
end
rule(quoted_string: simple(:string)) do
string.to_s
end
rule(token: simple(:string)) do
string.to_s
end
end
def require_signature!
render plain: signature_verification_failure_reason, status: signature_verification_failure_code unless signed_request_account
end
def signed_request?
request.headers['Signature'].present?
end
def signature_verification_failure_reason
@signature_verification_failure_reason
end
def signature_verification_failure_code
@signature_verification_failure_code || 401
end
def signature_key_id
signature_params['keyId']
rescue SignatureVerificationError
nil
end
def signed_request_account
return @signed_request_account if defined?(@signed_request_account)
raise SignatureVerificationError, 'Request not signed' unless signed_request?
raise SignatureVerificationError, 'Incompatible request signature. keyId and signature are required' if missing_required_signature_parameters?
raise SignatureVerificationError, 'Unsupported signature algorithm (only rsa-sha256 and hs2019 are supported)' unless %w(rsa-sha256 hs2019).include?(signature_algorithm)
raise SignatureVerificationError, 'Signed request date outside acceptable time window' unless matches_time_window?
verify_signature_strength!
verify_body_digest!
account = account_from_key_id(signature_params['keyId'])
raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if account.nil?
signature = Base64.decode64(signature_params['signature'])
compare_signed_string = build_signed_string
return account unless verify_signature(account, signature, compare_signed_string).nil?
account = stoplight_wrap_request { account.possibly_stale? ? account.refresh! : account_refresh_key(account) }
raise SignatureVerificationError, "Public key not found for key #{signature_params['keyId']}" if account.nil?
return account unless verify_signature(account, signature, compare_signed_string).nil?
@signature_verification_failure_reason = "Verification failed for #{account.username}@#{account.domain} #{account.uri} using rsa-sha256 (RSASSA-PKCS1-v1_5 with SHA-256)"
@signed_request_account = nil
rescue SignatureVerificationError => e
@signature_verification_failure_reason = e.message
@signed_request_account = nil
end
def request_body
@request_body ||= request.raw_post
end
private
def signature_params
@signature_params ||= begin
raw_signature = request.headers['Signature']
tree = SignatureParamsParser.new.parse(raw_signature)
SignatureParamsTransformer.new.apply(tree)
end
rescue Parslet::ParseFailed
raise SignatureVerificationError, 'Error parsing signature parameters'
end
def signature_algorithm
signature_params.fetch('algorithm', 'hs2019')
end
def signed_headers
signature_params.fetch('headers', signature_algorithm == 'hs2019' ? '(created)' : 'date').downcase.split(' ')
end
def verify_signature_strength!
raise SignatureVerificationError, 'Mastodon requires the Date header or (created) pseudo-header to be signed' unless signed_headers.include?('date') || signed_headers.include?('(created)')
raise SignatureVerificationError, 'Mastodon requires the Digest header or (request-target) pseudo-header to be signed' unless signed_headers.include?(Request::REQUEST_TARGET) || signed_headers.include?('digest')
raise SignatureVerificationError, 'Mastodon requires the Host header to be signed when doing a GET request' if request.get? && !signed_headers.include?('host')
raise SignatureVerificationError, 'Mastodon requires the Digest header to be signed when doing a POST request' if request.post? && !signed_headers.include?('digest')
end
def verify_body_digest!
return unless signed_headers.include?('digest')
raise SignatureVerificationError, 'Digest header missing' unless request.headers.key?('Digest')
digests = request.headers['Digest'].split(',').map { |digest| digest.split('=', 2) }.map { |key, value| [key.downcase, value] }
sha256 = digests.assoc('sha-256')
raise SignatureVerificationError, "Mastodon only supports SHA-256 in Digest header. Offered algorithms: #{digests.map(&:first).join(', ')}" if sha256.nil?
raise SignatureVerificationError, "Invalid Digest value. Computed SHA-256 digest: #{body_digest}; given: #{sha256[1]}" if body_digest != sha256[1]
end
def verify_signature(account, signature, compare_signed_string)
if account.keypair.public_key.verify(OpenSSL::Digest.new('SHA256'), signature, compare_signed_string)
@signed_request_account = account
@signed_request_account
end
rescue OpenSSL::PKey::RSAError
nil
end
def build_signed_string
signed_headers.map do |signed_header|
if signed_header == Request::REQUEST_TARGET
"#{Request::REQUEST_TARGET}: #{request.method.downcase} #{request.path}"
elsif signed_header == '(created)'
raise SignatureVerificationError, 'Invalid pseudo-header (created) for rsa-sha256' unless signature_algorithm == 'hs2019'
raise SignatureVerificationError, 'Pseudo-header (created) used but corresponding argument missing' if signature_params['created'].blank?
"(created): #{signature_params['created']}"
elsif signed_header == '(expires)'
raise SignatureVerificationError, 'Invalid pseudo-header (expires) for rsa-sha256' unless signature_algorithm == 'hs2019'
raise SignatureVerificationError, 'Pseudo-header (expires) used but corresponding argument missing' if signature_params['expires'].blank?
"(expires): #{signature_params['expires']}"
else
"#{signed_header}: #{request.headers[to_header_name(signed_header)]}"
end
end.join("\n")
end
def matches_time_window?
created_time = nil
expires_time = nil
begin
if signature_algorithm == 'hs2019' && signature_params['created'].present?
created_time = Time.at(signature_params['created'].to_i).utc
elsif request.headers['Date'].present?
created_time = Time.httpdate(request.headers['Date']).utc
end
expires_time = Time.at(signature_params['expires'].to_i).utc if signature_params['expires'].present?
rescue ArgumentError
return false
end
expires_time ||= created_time + 5.minutes unless created_time.nil?
expires_time = [expires_time, created_time + EXPIRATION_WINDOW_LIMIT].min unless created_time.nil?
return false if created_time.present? && created_time > Time.now.utc + CLOCK_SKEW_MARGIN
return false if expires_time.present? && Time.now.utc > expires_time + CLOCK_SKEW_MARGIN
true
end
def body_digest
@body_digest ||= Digest::SHA256.base64digest(request_body)
end
def to_header_name(name)
name.split(/-/).map(&:capitalize).join('-')
end
def missing_required_signature_parameters?
signature_params['keyId'].blank? || signature_params['signature'].blank?
end
def account_from_key_id(key_id)
domain = key_id.start_with?('acct:') ? key_id.split('@').last : key_id
if domain_not_allowed?(domain)
@signature_verification_failure_code = 403
return
end
if key_id.start_with?('acct:')
stoplight_wrap_request { ResolveAccountService.new.call(key_id.gsub(/\Aacct:/, '')) }
elsif !ActivityPub::TagManager.instance.local_uri?(key_id)
account = ActivityPub::TagManager.instance.uri_to_resource(key_id, Account)
account ||= stoplight_wrap_request { ActivityPub::FetchRemoteKeyService.new.call(key_id, id: false) }
account
end
rescue Mastodon::HostValidationError
nil
end
def stoplight_wrap_request(&block)
Stoplight("source:#{request.remote_ip}", &block)
.with_fallback { nil }
.with_threshold(1)
.with_cool_off_time(5.minutes.seconds)
.with_error_handler { |error, handle| error.is_a?(HTTP::Error) || error.is_a?(OpenSSL::SSL::SSLError) ? handle.call(error) : raise(error) }
.run
end
def account_refresh_key(account)
return if account.local? || !account.activitypub?
ActivityPub::FetchRemoteAccountService.new.call(account.uri, only_key: true)
end
end