Protean signatures (PSs), recently introduced by Krenn et al. (CANS ‘18), allow a semi-trusted third party (the sanitiser), to modify a signed message in a controlled way: the signer can define the message parts to be arbitrarily editable by the sanitiser, as well as message parts which can be redacted (but not altered otherwise) by the sanitiser. Thus, PSs generalise both redactable signatures (RSs) and sanitisable signatures (SSs) into a single notion. Invisibility for PSs guarantees that no outsider (i.e. any party not being signer or sanitiser) can decide which message parts can be edited. However, the current definition of invisibility does not prohibit that an outsider can decide which parts are redactable – only which parts can be edited are hidden. This negatively impacts the privacy guarantees provided by this definition. The authors extend PSs to be fully invisible. Their notion guarantees that an outsider can identify neither editable nor redactable parts. They, therefore, introduce the new notions of invisible RSs and invisible non-accountable SSs ( S S ′ ), along with a consolidated framework for aggregate signatures. Using those building blocks, their resulting construction is significantly more efficient than the original scheme by Krenn et al., which they demonstrate in a prototypical implementation.

中文翻译：

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完全隐形的Protean签名方案

Krenn等人最近引入了Protean签名（PSs）。（CANS '18），允许半受信任的第三方（卫生人员）以受控方式修改已签名的消息：签名人可以定义卫生人员可以任意编辑的消息部分以及可以由消毒剂编辑（但不得以其他方式更改）。因此，PS将可编辑签名（RSs）和可卫生签名（SSs）都概括为一个概念。PS的隐身性保证了没有任何局外人（即，不是签名者或消毒者的任何一方）可以决定可以编辑哪些消息部分。但是，当前对隐身的定义并不禁止局外人可以决定哪些部分是可编辑的-仅隐藏哪些部分可以编辑。这会对此定义提供的隐私保证产生负面影响。作者将PS扩展为完全不可见。他们的观点保证了局外人无法识别可编辑部分或可编辑部分。因此，他们引入了不可见的RS和不可见的不负责任的SS（SS'）的新概念，以及用于集合签名的合并框架。使用这些构建块，它们产生的构造比Krenn等人的原始方案（在原型实现中进行演示）要有效得多。