US Patent 11917062 Key rotation verification without decryption

Key rotation verification without decryption is provided. Two ciphertext inputs encrypted from a plaintext input by an encryption function using different cryptographic keys are input, wherein the encryption function is selected from a function family having an output space of one or more convex sets. A divergence between the two ciphertext inputs is computed. A membership oracle is executed on the two ciphertext inputs, wherein the two ciphertext inputs are determined to be members of the same convex set of the one or more convex sets if the computed divergence satisfies a separation condition. The two ciphertext inputs are validated to both correspond to the same plaintext input, responsive to determining that the two ciphertext inputs are members of the same convex set, wherein the two ciphertext inputs do not correspond to the same plaintext input if the two ciphertext inputs are not members of the same convex set.