@api private
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 30 def call(context) attach_http_event_listeners(context) @handler.call(context) end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 37 def attach_http_event_listeners(context) context.http_response.on_headers(200) do cipher = decryption_cipher(context) decrypter = body_contains_auth_tag?(context) ? authenticated_decrypter(context, cipher) : IODecrypter.new(cipher, context.http_response.body) context.http_response.body = decrypter end context.http_response.on_success(200) do decrypter = context.http_response.body decrypter.finalize decrypter.io.rewind if decrypter.io.respond_to?(:rewind) context.http_response.body = decrypter.io end context.http_response.on_error do if context.http_response.body.respond_to?(:io) context.http_response.body = context.http_response.body.io end end end
When the x-amz-meta-x-amz-tag-len header is present, it indicates that the body of this object has a trailing auth tag. The header indicates the length of that tag.
This method fetches the tag from the end of the object by making a GET Object w/range request. This auth tag is used to initialize the cipher, and the decrypter truncates the auth tag from the body when writing the final bytes.
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 143 def authenticated_decrypter(context, cipher) http_resp = context.http_response content_length = http_resp.headers['content-length'].to_i auth_tag_length = http_resp.headers['x-amz-meta-x-amz-tag-len'] auth_tag_length = auth_tag_length.to_i / 8 auth_tag = context.client.get_object( bucket: context.params[:bucket], key: context.params[:key], range: "bytes=-#{auth_tag_length}" ).body.read cipher.auth_tag = auth_tag cipher.auth_data = '' # The encrypted object contains both the cipher text # plus a trailing auth tag. This decrypter will the body # expect for the trailing auth tag. decrypter = IOAuthDecrypter.new( io: http_resp.body, encrypted_content_length: content_length - auth_tag_length, cipher: cipher) end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 167 def body_contains_auth_tag?(context) context.http_response.headers['x-amz-meta-x-amz-tag-len'] end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 61 def decryption_cipher(context) if envelope = get_encryption_envelope(context) context[:encryption][:cipher_provider].decryption_cipher(envelope) else raise Errors::DecryptionError, "unable to locate encyrption envelope" end end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 87 def envelope_from_instr_file(context) suffix = context[:encryption][:instruction_file_suffix] possible_envelope = Json.load(context.client.get_object( bucket: context.params[:bucket], key: context.params[:key] + suffix ).body.read) extract_envelope(possible_envelope) rescue S3::Errors::ServiceError, Json::ParseError nil end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 77 def envelope_from_metadata(context) possible_envelope = {} POSSIBLE_ENVELOPE_KEYS.each do |suffix| if value = context.http_response.headers["x-amz-meta-#{suffix}"] possible_envelope[suffix] = value end end extract_envelope(possible_envelope) end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 98 def extract_envelope(hash) return v1_envelope(hash) if hash.key?('x-amz-key') return v2_envelope(hash) if hash.key?('x-amz-key-v2') if hash.keys.any? { |key| key.match(/^x-amz-key-(.+)$/) } msg = "unsupported envelope encryption version #{$1}" raise Errors::DecryptionError, msg else nil # no envelope found end end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 69 def get_encryption_envelope(context) if context[:encryption][:envelope_location] == :metadata envelope_from_metadata(context) || envelope_from_instr_file(context) else envelope_from_instr_file(context) || envelope_from_metadata(context) end end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 109 def v1_envelope(envelope) envelope end
# File lib/aws-sdk-resources/services/s3/encryption/decrypt_handler.rb, line 113 def v2_envelope(envelope) unless POSSIBLE_ENCRYPTION_FORMATS.include? envelope['x-amz-cek-alg'] alg = envelope['x-amz-cek-alg'].inspect msg = "unsupported content encrypting key (cek) format: #{alg}" raise Errors::DecryptionError, msg end unless envelope['x-amz-wrap-alg'] == 'kms' # possible to support # RSA/ECB/OAEPWithSHA-256AndMGF1Padding alg = envelope['x-amz-wrap-alg'].inspect msg = "unsupported key wrapping algorithm: #{alg}" raise Errors::DecryptionError, msg end unless V2_ENVELOPE_KEYS.sort == envelope.keys.sort msg = "incomplete v2 encryption envelope:\n" msg += " expected: #{V2_ENVELOPE_KEYS.join(',')}\n" msg += " got: #{envelope_keys.join(', ')}" raise Errors::DecryptionError, msg end envelope end