167 lines
8.5 KiB
Ruby
167 lines
8.5 KiB
Ruby
# frozen_string_literal: true
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require "cbor"
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require "cose"
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module DiscourseWebauthn
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class RegistrationService < BaseValidationService
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##
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# See https://w3c.github.io/webauthn/#sctn-registering-a-new-credential for
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# the registration steps followed here. Memoized methods are called in their
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# place in the step flow to make the process clearer.
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def register_security_key
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# 4. Verify that the value of C.type is webauthn.create.
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validate_webauthn_type(::DiscourseWebauthn::ACCEPTABLE_REGISTRATION_TYPE)
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# 5. Verify that the value of C.challenge equals the base64url encoding of options.challenge.
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validate_challenge
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# 6. Verify that the value of C.origin matches the Relying Party's origin.
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validate_origin
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# 7. Verify that the value of C.tokenBinding.status matches the state of Token Binding for the TLS
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# connection over which the assertion was obtained. If Token Binding was used on that TLS connection,
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# also verify that C.tokenBinding.id matches the base64url encoding of the Token Binding ID for the connection.
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# Not using this right now.
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# 8. Let hash be the result of computing a hash over response.clientDataJSON using SHA-256.
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client_data_hash
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# 9. Perform CBOR decoding on the attestationObject field of the AuthenticatorAttestationResponse
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# structure to obtain the attestation statement format fmt, the authenticator data authData,
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# and the attestation statement attStmt.
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attestation
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# 10. Verify that the rpIdHash in authData is the SHA-256 hash of the RP ID expected by the Relying Party.
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# check the SHA256 hash of the rpId is the same as the authData bytes 0..31
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validate_rp_id_hash
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# 11. Verify that the User Present bit of the flags in authData is set.
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# https://blog.bigbinary.com/2011/07/20/ruby-pack-unpack.html
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#
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validate_user_presence
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#
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# 12. If user verification is required for this registration, verify that
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# the User Verified bit of the flags in authData is set.
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validate_user_verification if @factor_type == UserSecurityKey.factor_types[:first_factor]
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# 13. Verify that the "alg" parameter in the credential public key in authData matches the alg
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# attribute of one of the items in options.pubKeyCredParams.
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# https://w3c.github.io/webauthn/#table-attestedCredentialData
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# See https://www.iana.org/assignments/cose/cose.xhtml#algorithms for supported algorithm
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# codes.
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credential_public_key, credential_public_key_bytes, credential_id =
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extract_public_key_and_credential_from_attestation(auth_data)
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if ::DiscourseWebauthn::SUPPORTED_ALGORITHMS.exclude?(credential_public_key.alg)
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raise(
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UnsupportedPublicKeyAlgorithmError,
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I18n.t("webauthn.validation.unsupported_public_key_algorithm_error"),
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)
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end
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# 14. Verify that the values of the client extension outputs in clientExtensionResults and the authenticator
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# extension outputs in the extensions in authData are as expected, considering the client extension input
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# values that were given in options.extensions. In particular, any extension identifier values in the
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# clientExtensionResults and the extensions in authData MUST also be present as extension identifier values
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# in options.extensions, i.e., no extensions are present that were not requested. In the general case, the
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# meaning of "are as expected" is specific to the Relying Party and which extensions are in use.
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# Not using this right now.
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# 15. Determine the attestation statement format by performing a USASCII case-sensitive match on fmt against the
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# set of supported WebAuthn Attestation Statement Format Identifier values. An up-to-date list of registered
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# WebAuthn Attestation Statement Format Identifier values is maintained in the IANA registry of the same
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# name [WebAuthn-Registries].
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# 16. Verify that attStmt is a correct attestation statement, conveying a valid attestation signature,
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# by using the attestation statement format fmt’s verification procedure given attStmt, authData and hash.
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if ::DiscourseWebauthn::VALID_ATTESTATION_FORMATS.exclude?(attestation["fmt"]) ||
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attestation["fmt"] != "none"
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raise(
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UnsupportedAttestationFormatError,
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I18n.t("webauthn.validation.unsupported_attestation_format_error"),
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)
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end
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#==================================================
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# ONLY APPLIES IF fmt !== none, this is all to do with
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# verifying attestation. May want to come back to this at
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# some point for additional security.
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#==================================================
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#
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# 17. If validation is successful, obtain a list of acceptable trust anchors (attestation root certificates or
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# ECDAA-Issuer public keys) for that attestation type and attestation statement format fmt, from a trusted
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# source or from policy. For example, the FIDO Metadata Service [FIDOMetadataService] provides one way
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# to obtain such information, using the aaguid in the attestedCredentialData in authData.
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#
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# 18. Assess the attestation trustworthiness using the outputs of the verification procedure in step 16, as follows:
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# If no attestation was provided, verify that None attestation is acceptable under Relying Party policy.
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#==================================================
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# 19. Check that the credentialId is not yet registered to any other user. If registration
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# is requested for a credential that is already registered to a different user,
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# the Relying Party SHOULD fail this registration ceremony, or it MAY decide to accept
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# the registration, e.g. while deleting the older registration.
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encoded_credential_id = Base64.strict_encode64(credential_id)
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encoded_public_key = Base64.strict_encode64(credential_public_key_bytes)
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if UserSecurityKey.exists?(credential_id: encoded_credential_id)
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raise(CredentialIdInUseError, I18n.t("webauthn.validation.credential_id_in_use_error"))
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end
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# 20. If the attestation statement attStmt verified successfully and is found to be trustworthy,
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# then register the new credential with the account that was denoted in options.user, by
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# associating it with the credentialId and credentialPublicKey in the attestedCredentialData
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# in authData, as appropriate for the Relying Party's system.
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UserSecurityKey.create!(
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user: @current_user,
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credential_id: encoded_credential_id,
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public_key: encoded_public_key,
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name: @params[:name],
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factor_type: @factor_type,
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)
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rescue CBOR::UnpackError, CBOR::TypeError, CBOR::MalformedFormatError, CBOR::StackError
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raise MalformedAttestationError, I18n.t("webauthn.validation.malformed_attestation_error")
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end
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private
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def attestation
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@attestation ||= CBOR.decode(Base64.decode64(@params[:attestation]))
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end
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def auth_data
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@auth_data ||= attestation["authData"]
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end
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def extract_public_key_and_credential_from_attestation(auth_data)
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# see https://w3c.github.io/webauthn/#authenticator-data for lengths
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# of authdata for extraction
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rp_id_length = 32
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flags_length = 1
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sign_count_length = 4
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attested_credential_data_start_position = rp_id_length + flags_length + sign_count_length # 37
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attested_credential_data_length = auth_data.size - attested_credential_data_start_position
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attested_credential_data =
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auth_data[
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attested_credential_data_start_position..(
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attested_credential_data_start_position + attested_credential_data_length - 1
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)
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]
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# see https://w3c.github.io/webauthn/#attested-credential-data for lengths
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# of data for extraction
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aa_guid = attested_credential_data[0..15]
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credential_id_length = attested_credential_data[16..17].unpack("n*")[0]
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credential_id = attested_credential_data[18..(18 + credential_id_length - 1)]
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public_key_start_position = 18 + credential_id_length
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public_key_bytes =
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attested_credential_data[
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public_key_start_position..(public_key_start_position + attested_credential_data.size - 1)
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]
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public_key = COSE::Key.deserialize(public_key_bytes)
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[public_key, public_key_bytes, credential_id]
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end
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end
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end
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