Quantum cryptographic definitions are often sensitive to the number of copies of the cryptographic states revealed to an adversary. Making definitional changes to the number of copies accessible to an adversary can drastically affect various aspects including the computational hardness, feasibility, and applicability of the resulting cryptographic scheme. This phenomenon appears in many places in quantum cryptography, including quantum pseudorandomness and unclonable cryptography. To address this, we present a generic approach to boost single-copy security to multi-copy security and apply this approach to many settings. As a consequence, we obtain the following new results: -One-copy stretch pseudorandom state generators (under mild assumptions) imply the existence of t-copy stretch pseudorandom state generators, for any fixed polynomial t. -One-query pseudorandom unitaries with short keys (under mild assumptions) imply the existence of t-query pseudorandom unitaries with short keys, for any fixed polynomial t. -Assuming indistinguishability obfuscation and other standard cryptographic assumptions, there exist identical-copy secure unclonable primitives such as public-key quantum money and quantum copy-protection.

翻译：量子密码学定义通常对向敌手公开的密码态拷贝数量较为敏感。改变敌手可访问的拷贝数量可能显著影响密码方案的多个方面，包括计算难度、可行性与适用性。这种现象广泛存在于量子密码学的诸多领域，如量子伪随机性与不可克隆密码学。为此，我们提出一种将单拷贝安全性提升至多拷贝安全性的通用方法，并将该方法应用于多种场景。基于此，我们获得了以下新结果：-（在温和假设下）单拷贝可拉伸伪随机态生成器蕴含任意固定多项式t对应的t拷贝可拉伸伪随机态生成器的存在性。-（在温和假设下）具有短密钥的单查询伪随机酉算子蕴含任意固定多项式t对应的具有短密钥的t查询伪随机酉算子的存在性。-在假设不可区分混淆及其他标准密码学假设成立的前提下，存在具有相同拷贝安全性的不可克隆密码原语，例如公钥量子货币与量子复制保护方案。