Forward-Secure Crash-Resilient Logging Device

Abstract

A logging device configured to store log messages, includes a storage device having a plurality of log entry locations which can be ordered as a sequence, an encryption device configured to generate the encrypted log messages from log messages, an authentication code generator configured to generate an authentication code from the encrypted log message, a key evolving device, a state storage device configured to store state variables for use by the encryption device, the authentication code generator and/or the key evolving device. Furthermore, a verification device configured to verify log entries stored in log entry locations of the storage device is also described. A method for storing log entries in log entry locations of a storage device of a logging device as well as to a method for verifying the integrity of log entries stored in log entry locations of a storage device is also described.

1 . A logging device configured to store log messages, comprising:
 a storage device having a plurality of log entry locations configured to be ordered as a sequence;   an encryption device configured to generate encrypted log messages from log messages;   an authentication code generator configured to generate an authentication code from an encrypted log message;   a key evolving device; and   a state storage device,   wherein the state storage device is configured to store state variables for use by at least one of the encryption device, the authentication code generator, and the key evolving device,   wherein each of the log entry locations is configured to provide storage space for a log entry,   wherein the key evolving device is configured to provide a deterministic sequence of secrets from an initial status, and   wherein the logging device comprises a position determination device configured to determine a random log entry location in which a given log entry is to be stored.   
     
     
         2 . The logging device of  claim 1 , wherein the position determination device is configured to choose the log entry locations using a pseudo-random sequence of locations calculated from an initial status. 
     
     
         3 . The logging device according to  claim 1 , wherein the position determination device is configured to produce a plurality of dummy entries as part of an initialization,
 wherein the position determination device is configured to only use as many log entry locations as there are log entries and dummy entries, and   wherein the position determination device is configured, when an additional log entry is to be stored, to instruct the storage device to move a previously stored log entry from a selected log entry location into an additional log entry location and to store the additional log entry in the selected log entry location.   
     
     
         4 . A verification device configured to verify log entries stored in log entry locations of the storage device of the logging device according to  claim 1 , comprising:
 a state storage device; and   a key evolving device,   wherein the key evolving device is configured to produce a sequence of secrets from an initial status,   wherein the key evolving device is configured to produce a sequence of secrets that is identical to the sequence of secrets produced by the key evolving device of the logging device if the initial status provided is identical, and   wherein the verification device is configured to verify the integrity of log entries stored in log entry locations by calculating authentication codes from encrypted log messages and the sequence of secrets.   
     
     
         5 . A method of storing log entries in log entry locations of a storage device of a logging device comprising:
 encrypting a log message using a secret to create an encrypted log message;   calculating an authentication code from the secret and the encrypted log message to create a log entry comprising the encrypted log message and the authentication code; and   determining a random one of the log entry locations to become a selected log entry location for storing the log entry;   wherein the selected log entry location is determined by using a pseudo random function.   
     
     
         6 . The method of  claim 5 , wherein a plurality of dummy log entries is created during an initialisation phase. 
     
     
         7 . The method of  claim 5 , wherein the log entry locations are organized as a numbered sequence, in that only as many log entry locations are used as there are log entries and dummy log entries to be stored and in that an unbroken sequence of log entry locations is used to store the log entries and the dummy log entries. 
     
     
         8 . The method of  claim 7 , wherein, when a new log entry is to be stored, the method further comprising:
 determining a new log entry location to be added to the unbroken sequence of log entry locations as a new log entry location;   determining the selected log entry location from the previously used log entry location using a pseudorandom generator;   copying the log entry stored in the selected log entry location to the new log entry location; and   storing the new log entry in the selected log entry location.   
     
     
         9 . The method according to  claim 7 , wherein the unbroken sequence of log entry locations is chosen so that the unbroken sequence starts at the first log entry location of the storage device.