One embodiment relates to a data processing system having a cryptographic unit. The cryptographic unit includes cryptographic circuitry which performs a first cryptographic function to provide security for a portion of the cryptographic unit, and which performs a second cryptographic function to provide security for a portion of the data processing system external to the cryptographic unit. The cryptographic unit may therefore operate in a normal operating mode and in a secure operating mode. During a first secure operating mode a first key is used to decrypt first security configuration information which includes a second key. During a second secure operating mode, the second key is used to decrypt second security configuration information. The cryptographic unit may include a secure internal memory such that during the secure operating modes, the cryptographic unit may only process descriptors provided from this secure internal memory.