Digitally Signed Document Sanitizing Scheme with Disclosure Condition Control

A digital signature does not allow any alteration of the document to which it is attached. Appropriate alteration of some signed documents, however, should be allowed because there are security requirements other than that for the integrity of the document. In the disclosure of official information, for example, sensitive information such as personal information or national secrets is masked when an official document is sanitized so that its nonsensitive information can be disclosed when it is demanded by a citizen. If this disclosure is done digitally by using the current digital signature schemes, the citizen cannot verify the disclosed information correctly because the information has been altered to prevent the leakage of sensitive information. That is, with current digital signature schemes, the confidentiality of official information is incompatible with the integrity of that information. This is called the digital document sanitizing problem, and some solutions such as digital document sanitizing schemes and content extraction signatures have been proposed. In this paper, we point out that the conventional digital signature schemes are vulnerable to additional sanitizing attack and show how this vulnerability can be eliminated by using a new digitally signed document sanitizing scheme with disclosure condition control. key words: digital signature, disclosure of official information, privacy issue