<p>This paper introduces <i>Recursive Shamir-Based Encryption</i> (RSBE), a symmetric encryption scheme designed with a crypto-agile and quantum-upgradeable architecture. RSBE integrates recursive applications of Shamir’s Secret Sharing with a terminal pseudorandom permutation. The plaintext is progressively transformed through multiple secret-sharing layers until a single final block remains, which is encrypted using a standard pseudorandom permutation (e.g., AES). The construction ensures that all computational security is concentrated in a single primitive invocation, while intermediate transformations provide structural diffusion and mixing across recursion levels. A dynamic threshold-selection mechanism enables operation over arbitrary message lengths, and optimized algebraic updates maintain efficient per-level computation. We prove IND-CPA security under the assumption that the underlying permutation is a secure pseudorandom permutation. The analysis highlights that the scheme reduces the surface of computational assumptions to a single block-cipher call, making it naturally adaptable to post-quantum settings by replacing or strengthening this component. Empirical results indicate competitive performance relative to AES-CBC/CTR. By distributing and aggregating data across recursive layers, RSBE provides a scalable encryption framework suitable for cloud-native storage and crypto-agile security deployment.</p>