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59 lines
2.3 KiB
Ruby
59 lines
2.3 KiB
Ruby
# frozen_string_literal: true
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# This is an implementation of https://codeberg.org/fediverse/fep/src/branch/main/fep/8b32/fep-8b32.md
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class ActivityPub::ObjectIntegrityProof
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include JsonLdHelper
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CONTEXT = 'https://w3id.org/identity/v1'
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SIGNATURE_CONTEXT = 'https://w3id.org/security/v1'
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def initialize(json)
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@json = json
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end
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def verify_actor!(proof_purpose: 'assertionMethod')
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return unless @json.is_a?(Hash) && @json['proof'].is_a?(Hash)
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proof = @json['proof']
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return unless proof['type'].present? && proof['verificationMethod'].present? && proof['proofPurpose'].present?
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return if proof_purpose != proof['proofPurpose'] || proof['type'] != 'DataIntegrityProof'
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return if proof['expires']&.to_datetime&.past?
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cryptosuite = proof['cryptosuite']
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key_uri = proof['verificationMethod']
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return unless cryptosuite == 'eddsa-jcs-2022' && proof['proofValue'].present?
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keypair = Keypair.from_keyid(key_uri)
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keypair = ActivityPub::FetchRemoteKeyService.new.call(key_uri) if keypair&.public_key.blank?
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return if keypair.nil? || !keypair.usable? || keypair.type != 'ed25519'
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keypair.actor if ActivityPub::ObjectIntegrityProof.verify_eddsa_jcs_2022(@json, keypair.keypair)
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rescue OpenSSL::PKey::RSAError
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false
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end
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# https://www.w3.org/TR/vc-di-eddsa/#verify-proof-eddsa-jcs-2022
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def self.verify_eddsa_jcs_2022(document, keypair) # rubocop:disable Naming/VariableNumber
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unsecured_document = document.without('proof')
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proof_options = document['proof'].without('proofValue')
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proof_bytes = Multibase.decode(document['proof']['proofValue'])
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if proof_options['@context'].present?
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return unless unsecured_document['@context'].is_a?(Array)
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return unless unsecured_document['@context'][...proof_options['@context'].length] == proof_options['@context']
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# Step 4.2. from the aforementioned algorithm, it's useful when vocabulary necessary to the cryptosuite had to be added on top of the to-be-signed document
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unsecured_document['@context'] = proof_options['@context']
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end
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transformed_data = unsecured_document.to_json_c14n
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proof_config = proof_options.to_json_c14n
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to_be_verified = Digest::SHA256.digest(proof_config) + Digest::SHA256.digest(transformed_data)
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keypair.verify(nil, proof_bytes, to_be_verified)
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end
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end
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