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种数字签名方案，其附加特性在于：从某条消息的签名中，任何一方均可提取该消息中（允许引用部分的）签名，而无需知晓私钥或与原始消息的签名者交互。关键在于，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Merkle树与经典数字签名方案构造了一个具体的可引用签名方案实例。该方案被证明满足上述安全性定义。此外，我们给出了所构造方案的复杂度上界，并提供了签名、引用及验证的算法。最后，我们探讨了可引用签名的具体应用场景，即通过增强社交媒体上真实内容的可信度来遏制虚假信息，既考虑其使用方法，也分析其缓解假新闻影响的潜在价值。