Secure key leasing (SKL) enables the holder of a secret key for a cryptographic function to temporarily lease the key using quantum information. Later, the recipient can produce a deletion certificate, which proves that they no longer have access to the secret key. The security guarantee ensures that even a malicious recipient cannot continue to evaluate the function, after producing a valid deletion certificate. Most prior work considers an adversarial recipient that obtains a single leased key, which is insufficient for many applications. In the more realistic collusion-resistant setting, security must hold even when polynomially many keys are leased (and subsequently deleted). However, achieving collusion-resistant SKL from standard assumptions remains poorly understood, especially for functionalities beyond decryption. We improve upon this situation by introducing new pathways for constructing collusion-resistant SKL. Our main contributions are as follows: - A generalization of quantum-secure collusion-resistant traitor tracing called multi-level traitor tracing (MLTT), and a compiler that transforms an MLTT scheme for a primitive X into a collusion-resistant SKL scheme for primitive X. - The first bounded collusion-resistant SKL scheme for PRFs, assuming LWE. - A compiler that upgrades any single-key secure SKL scheme for digital signatures into one with unbounded collusion-resistance, assuming OWFs. - A compiler that upgrades collusion-resistant SKL schemes with classical certificates to ones having verification-query resilience, assuming OWFs.

翻译：安全密钥租赁（SKL）允许密码函数秘密密钥的持有者通过量子信息临时租赁该密钥。随后，接收方可生成删除证明，以证实其不再拥有该秘密密钥的访问权限。安全保证确保即使恶意接收方在生成有效删除证明后，也无法继续评估该函数。现有研究大多考虑仅获取单个租赁密钥的对抗性接收方，这对于许多应用场景而言并不充分。在更具现实意义的抗合谋设定中，即使租赁（并随后删除）多项式数量的密钥，安全性也必须得以保持。然而，基于标准假设实现抗合谋SKL仍鲜为人知，尤其是在解密之外的功能领域。我们通过引入构建抗合谋SKL的新路径来改善这一现状。主要贡献如下：- 提出量子安全抗合谋叛逆者追踪的泛化形式——多级叛逆者追踪（MLTT），并构建将原始功能X的MLTT方案转换为原始功能X的抗合谋SKL方案的编译器。- 基于LWE假设，首次实现伪随机函数的有限抗合谋SKL方案。- 基于单向函数假设，构建将任意单密钥安全数字签名SKL方案升级为具备无限抗合谋能力的编译器。- 基于单向函数假设，构建将采用经典证书的抗合谋SKL方案升级为具备验证查询鲁棒性的编译器。