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，具有以下附加特性：从消息的签名中，任何一方均可提取该消息（允许范围内）引用的签名，而无需知晓原始消息签名者的私钥或与之交互。关键在于，提取的签名仍使用原始私钥进行签名。我们定义了可引用签名方案的安全概念，并利用Merkle树和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。该方案被证明相对于前述安全概念是安全的。此外，我们证明了所构造方案的复杂度界限，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，包括利用其通过增强社交媒体上的可信内容来打击虚假信息。我们既考虑了可引用签名的使用方法，也论证了为何使用它们可能有助于缓解假新闻的影响。