Quotable signature schemes are digital signature schemes with the additional property that from the signature for a message, any party can extract signatures for (allowable) quotes from the message, without knowing the secret key or interacting with the signer of the original message. Crucially, the extracted signatures are still signed with the original secret key. We define a notion of security for quotable signature schemes and construct a concrete example of a quotable signature scheme, using Merkle trees and classical digital signature schemes. The scheme is shown to be secure, with respect to the aforementioned notion of security. Additionally, we prove bounds on the complexity of the constructed scheme and provide algorithms for signing, quoting, and verifying. Finally, concrete use cases of quotable signatures are considered, using them to combat misinformation by bolstering authentic content on social media. We consider both how quotable signatures can be used, and why using them could help mitigate the effects of fake news.

翻译：可引用签名方案是一类数字签名方案，其附加特性是：从任意消息的签名中，任何实体均可在不知晓原始签名者私钥或与其交互的情况下，提取该消息（允许引用部分）的签名。关键之处在于，提取的签名仍由原始私钥签署。我们定义了可引用签名方案的安全性概念，并利用默克尔树与经典数字签名方案构建了一个具体的可引用签名实例。该方案被证明在所述安全性概念下是安全的。此外，我们给出了所构建方案的复杂度下界，并提供了签名、引用和验证的算法。最后，我们探讨了可引用签名的具体应用场景，即通过强化社交媒体上的真实内容来对抗虚假信息。我们既考虑了可引用签名的使用方式，也分析了其如何有助于缓解假新闻的影响。