Key management system for mixed-trust environments

Abstract

The invention allows for transporting, in different degrees of security strength, a symmetric key encrypted using an asymmetric encryption technique, and along with this transporting ciphertext derived from plaintext encrypted under this symmetric key. The encryptor encrypts the plaintext using a symmetric whose strength is commensurate with the trust level of the environment in which the encryptor is located. The encryptor encrypts this symmetric key for one or more intended recipients using an asymmetric technique commensurate with a high-trust environment. In the case of the encryptor residing in the low-trust environment, the encryptor additionally encrypts this symmetric key using an asymmetric encryption public key of the originator itself (or alternatively, that of a third party). Decryption equipment in all environments uses the decryption process corresponding to an algorithm identifier included by the originator. In all cases, the asymmetric encryption/decryption process used for each specific recipient is of a strength commensurate with the trust level of that recipient's own environment.