Has ISO 27001 give any recommendation or rules to be respected on usage of documents based on their level of classification. for example: a document classified confidential, is it permitted to be saved on public cloud, on which conditions.
ISO 27001 does not prescribe how to handle the information according to their classification level. Such treatment must be based on results of risk assessment and applicable legal requirements (e.g., laws, regulations, and contracts). For example, if the risks related to keeping confidential information on the public cloud are unacceptable, then one rule to be defined is that confidential documents must not be kept on the public cloud. Another example is that a contractual clause may define that confidential documents must be kept on local servers.