DE10248542A1 - Protecting log files involves data processing system security module providing information for each entry in log file, whereby each entry has associated function value, especially digital signature - Google Patents

Abstract

The method involves protecting log files with a data processing system against prohibited changes by generating a second entry for an entry in the log file. The data processing system has a security module that provides, especially continuous, information for each entry in the log file and whereby each entry has an associated function value, especially a digital signature, determined at least from the information and the entry.

Description

The invention relates to a method to secure log files using a data processing system unauthorized change, where a second entry is generated for an entry in the log file becomes.

Log files are known, e.g. allowed Access and unauthorized manipulation of the data on a computer or to be able to distinguish on the computer itself. In these log files certain actions on the data or on the computer are logged, to e.g. recognize an error or attack and the cause to be able to narrow it down. However, these log files themselves are generally not against manipulation protected.

It is still known log files by using e.g. to protect cryptographic hash functions. A A special feature is the so-called one-way hash function, in which the determined one Hash values cannot be inferred from the inputs. Such hash functions must be collision free, which means that no two different ones Inputs can be found (manual or machine) from which the same hash value is generated (although there are of course such couples often exists).

A particularly simple example a hash function represents the register of an address book in which infinite number of the finite set of letters of the alphabet name entries can be assigned. However, this simple hash function is not collision-free.

The general rule is that a one-way hash function H assigns a hash value h = H (N) to an arbitrarily long message N, e.g. always fixed length e.g. 128, 160, 192 or 256 bit. As mentioned it is difficult to impossible deduce the message N from a given hash value h.

So there is a known application the possibility on a transmitted Message N to apply the hash function H and the hash value h2 = H (N) with a transmitted in parallel Compare hash value h1 to see if the message on the way of transmission was manipulated. Manipulation is free if h2 = h1, i.e. the hash values match.

In this way e.g. also those mentioned Protected log files by adding a hash value for each data entry in the log file is calculated. To further secure this method, it is known calculate a hash value for each new entry in the log file is based on the new data entry and the previous hash value. The The current hash value is thus a short version of the entire previous one Logfiles. This method is also known as the "eternal log file".

A typical log file of this type can look like this, for example: Data1 h1 = H (Data1) Data2 h2 = H (h1, Data1) data3 h3 = H (h2, Data2) etc. if H represents the hash function.

Hash functions as such are Generally known to a person skilled in the art and need no further explanation. Known Algorithms are e.g. MD5, developed by Ronal L. Rivest, the National Security Agency (NSA) SHA-1 (Secure Hash Algorithm) the USA and the so-called Tiger algorithm by Eli Biham and Ross Anderson.

Another backup of hash functions offers the use of keys, which means that one calculated by such a key-dependent hash function Hash value can only be verified if the verifying one Person the key is known about the hash function. Such key-dependent hash functions will be also known as MAC (Message Authentication Code).

It is also known data and / or Protect messages with a digital signature, or with one the possibility to open, to be able to determine whether a message has been tampered with.

A digital signature thus forms a kind of fingerprint of the data or the message or a kind of integrity seal. Typical for a digital signature is a key pair consisting of one private and a public Key. The signature of a message or data is made using the cryptographic private key generated by means of the public key from the recipient to check the integrity of the data or the message. So can the recipient check, whether manipulation has taken place.

Because the application of an algorithm comparably slow to create a digital signature the data is known first by compressing a hash function and then compressing it onto this apply the digital signature.

A disadvantage of using a hash function on the newly added data in a log file, e.g. in a perpetual log file, is that the method described above offers no protection against deleting the last n entries from the log file and against new m entries replace, whereby the manipulator or a computer virus can calculate the new hash values so that this manipulation is not noticeable. A further disadvantage is that with the perpetual log file, all data ever hashed must be stored indefinitely. If even one of these data records is lost, it is lost the eternal log file has its evidential value.

The object of the invention is a to provide improved protection of log files to make one Make manipulation recognizable.

This object is achieved according to the invention solved, that the data processing system comprises a security module, which for each entry in the log file has a, in particular continuous, Provides information and each entry has a function value, in particular a digital signature is assigned to the at least is determined from the information and the entry.

This function value can be formed are by any mathematical function, preferably by a digital signature, a hash function, in particular a one-way hash function, or a MAC.

The use of such a disposal The information provided has the advantage that manipulation is noticeable because a computer virus or a manipulating person e.g. in the Removal and replacement of data is not known with which additional Information on the new data the algorithm will be applied got to.

The method according to the invention is particularly simple, if the information is a continuous numerical value.

It is also advantageous if the security module, which e.g. is designed as a chip card, both the additional Provides information as well as the application of the algorithm or the function, in particular a digital signature or MAC performs. The chip card is implemented e.g. in accordance with DIN-17.4, which specifies the specifications according to SigG and SigV.

To accelerate the formation of functional values and for further securing it can preferably be provided that before determining this functional value, especially the signature, a first algorithm, in particular a hash function, on at least the entry for determining a first value is used and the determination of the functional value, in particular the signature, at least based on the information and the calculated first value.

This first value can be formed by any mathematical algorithm, preferably by a hash function, in particular a one-way hash function, a digital signature, or a MAC.

In a special configuration The method can furthermore provide that the first value for an entry and the first value of a previous entry, especially all previous entries and / or first values are calculated. This in turn corresponds to that Updating the log file in the sense of the aforementioned "perpetual Log files ".

A concrete embodiment the invention is described below.

According to the basic idea of the method according to the invention, a function value fn, which supplements the log file, is formed in a log file for each new continuous data entry Data at the nth position of the log file on the basis of the function F. The safety module provides information In to form this function value fn. Accordingly, a log file can have the following structure:
Data1 f1 = F (I1, Data1)
Data2 f2 = F (I2, Data2)
Datan fn = F (In, Datan)

In the preferred form, a first algorithm A can be used before the function F is used to form a first value, so that the following structure of the log file results:
Data1 f1 = F (I1, A (Data1))
Data2 f2 = F (I2, A (Data2))
Datan fn = F (In, A (Datan))

In order to update the log file (in the sense of an eternal log file), algorithm A can be applied not only to the respective new entry Data, but also to the previously calculated first values An-1 and / or the previous function values fn-1. This results, for example, in the following structure of the log file:
Data1 f1 = F (I1, A (Data1))
Data2 f2 = F (I2, A (A1, Data2)) with A1 = A (Data1)
Datan fn = F (In, A (An-1, Datan)) with An-1 = A (Datan-1) or:
Data1 f1 = F (I1, A (Data1))
Data2 f2 = F (I2, A (f1, Data2)) with f1 = F (I1, A (Data1))
Datan fn = F (In, A (fn-1, Datan)) with fn-1 = F (In-1, A (fn-1, Datan-1))

As mentioned above, a hash function, a digital signature or a MAC or any other mathematical function can be used for the function F and for the algorithm A, for example. The information I provided by the security module can be, for example, a continuous numerical value 1, 2, 3, 4, 5, ... so that the following structure of a manipulated log file, for example, results:
Data1 sig1 = sig (1, hash (Data1))
Data2 sig2 = sig (2, hash (Data2))
Data3 sig3 = sig (3, hash (Data3))
Data3 + n sig3 + n = sig (3 + n, hash (Data3 + n))
Data3 + n + 1 sig3 + n + 1 = sig (3 + n + 1, hash (Data3 + n + 1))

A check of sig3 + n would show that not (4, hash (Data3 + n)) was signed, but (3 + n, hash (Data3 + n)) and the manipulation or gap in the log file would be obvious.

In a preferred embodiment the method involves communication between the computer, on which the log file is saved and the security module.

• 1. Der Computer berechnet hash(sig2, Data3) und sendet diesen Wert an das Sicherheitsmodul. Der Computer kann diese Berechnung durchführen, da er beide Werte kennt. Das Sicherheitsmodul wird durch diese Vorgehensweise von der Verarbeitung größerer Datenmengen entlastet, da ein großer Datensatz Data3 z. B. von einer Chipkarte nur sehr langsam verarbeitet werden könnte.
• 2. Das Sicherheitsmodul berechnet die digitale Signatur sig3 aus dem erhaltenen Wert hash(sig2, Data3) und einem internen Zählerwert, die in diesem Beispiel auf „3" gesetzt wurde. Dazu benötigt das Sicherheitsmodul einen privaten Schlüssel, der außerhalb des Sicherheitsmoduls nicht existiert. Das Sicherheitsmodul überträgt anschließend den Wert sig3 an den Computer.
• 3. Der Computer speichert sig3 an der vorgegebenen Stelle im Logfile.

In this example, the individual entries in the log file are linked by including the value of the signature for the previous entry in the signature of a new entry. (The value IV stands for the missing value sig0 in the sense of uniform data formats.) To generate sig3, for example, the following interaction between the computer and the security module takes place:

• 1. The computer calculates hash (sig2, Data3) and sends this value to the security module. The computer can do this calculation because it knows both values. This procedure relieves the security module of processing larger amounts of data, since a large data record Data3 e.g. B. could only be processed very slowly by a chip card.
• 2. The security module calculates the digital signature sig3 from the received value hash (sig2, Data3) and an internal counter value, which was set to "3" in this example. To do this, the security module needs a private key that does not exist outside the security module. The security module then transfers the value sig3 to the computer.
• 3. The computer saves sig3 at the specified location in the log file.

Claims (5)

Method for securing log files by means of a data processing system against unauthorized change, in which a second entry is generated for an entry in the log file, characterized in that the data processing system comprises a security module which, for each entry in the log file, has one, in particular provides continuous information and each entry is assigned a function value, in particular a digital signature, which is determined at least from the information and the entry. A method according to claim 1, characterized in that the information is a continuous numerical value. Method according to one of the preceding claims, characterized characterized that before determining the functional value, in particular the signature, a first algorithm, in particular a hash function, applied to at least the entry for determining a first value and the determination of the functional value, especially the signature, based at least on the information and the calculated first value is placed. A method according to claim 3, characterized in that the first value is calculated from an entry and the first Value of a previous entry or from an entry and the function value a previous entry, in particular all previous entries and / or first values. Method according to one of the preceding claims characterized that the function and / or the algorithm for education the first value as a digital signature and / or hash function and / or is designed as a MAC.