Kincses, Zoltán

Kincses Zoltán

University of Szeged

On Avoidance of Attacks Against the PIN Error Counter of SmartCardsZoltán KincsesSmart cards are generally considered as secure tokens, applicable for storage of long crypto-graphic keys or usable as keys themselves in different security mechanisms. However usuallythe access ability or usage of the internal data depends on the knowledge of a short PIN code.Counting the attempts of use with invalid PIN codes usually protects the card against simplebrute force attacks.If this PIN error counter can be somehow circumvented, an easy way opens to access datain the card without proper knowledge of the PIN code. The full paper of this detailed ab-stract describes attack methods - classical and newly invented also -, and suggests appropriatedefensive measures.Basic standards or programmer’s guide supplied with developer kits describe the role andthe mechanism of CHV (Card Holder Verification) and AUT (Authentication) bytes in a smartcard environment. The access control can be maintained through the management of asset ofcodes, which are commonly referred to as PIN (Personal Identity Number) codes. In general,the access of the data stored in a smart card is controlled by these PIN codes (PIN as basic code,PIN2 as security code, PUK as unlock code, and other more specific codes, like operator codefor higher security access to the chip or even supervisor code).Smart cards have their well-defined methods to handle the PIN management, from storageof these codes, through change possibility, till the counting of bad attempts.When the smart card’s PIN management system asks for a code to be entered, the presentedcode is compared with the stored one. If the given code does not match with the stored one,then the operating system will increment the counter of bad attempts. After reaching the maxi-mum number of allowed bad attempts, the OS will deny further attempts by blocking the code.The card can be used only after entering the unblock code. After receiving the correct code, thecounter will be reset to initial value.Analysing the security of the system from the PreDeCo (Preventive-Detective-Corrective)control’s point of view, the existing and the missing protection measures can be discovered.This way the weakest points in the security of the implemented system are easily identified.The preventive control against the user access is asking the PIN code. The detective control isthe counter of attempts and the corrective is the usage of an unblock code. From an attacker’spoint of view, however the preventive control is the counter of attempts, but if this control canbe circumvented, there is no detective or corrective control.The question is how it is possible to avoid or block the increment of the counter. The chipmust be operational for reading the data and compare the entered and the stored code, whileit must not be able writing the new counter value into memory. One is the manipulation ofalgorithm execution from outside and another is monitoring and manipulation of power con-sumption. Both have a simple protection method.The new attack method is the ’low temperature attack’. The aim is to reach that temperaturestate of the chip when it is able to process reading functions, but it is unable to process thewriting functions. Protection measures will be presented against this type of attack, and thisprotection can be applied in any other systems also, where the written data can be read backfor control purposes.In general, the suggested scheme - that is, the application of a secondary backup counterfor checking the correct increment of the error counter - can be applied in all cases when thesuccess of a memory write operation affects the security of the system.68

On avoidance of attacks against the PIN error counter of smart cards : [abstract]

http://acta.bibl.u-szeged.hu/59770/1/cscs_2004_068.pdf

On avoidance of attacks against the PIN error counter of smart cards

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