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diff --git a/paper/easycard.tex b/paper/easycard.tex new file mode 100644 index 0000000..ddc5be5 --- /dev/null +++ b/paper/easycard.tex @@ -0,0 +1,467 @@ +\documentclass[a4paper]{article} +\usepackage[english]{babel} +\usepackage{graphicx} +\usepackage{subfigure} +\pagestyle{plain} + +%\usepackage{url} + +\setlength{\oddsidemargin}{0in} +\setlength{\evensidemargin}{0in} +\setlength{\topmargin}{0in} +\setlength{\headheight}{0in} +\setlength{\headsep}{0in} +\setlength{\textwidth}{6.5in} +\setlength{\textheight}{9.5in} +%\setlength{\parindent}{0in} +\setlength{\parskip}{0.05in} + +\begin{document} + +\title{Security analysis of the EasyCard payment card in Taiwan} +\author{Harald Welte $<$laforge@gnumonks.org$>$} +\date{August 31, 2010} +\maketitle + +\begin{abstract} +The EasyCard system, established in 2001, is the most popular store-valued card +in Taiwan. With more than 18 million issued cards, it is the predominant means +of paying for public transportation services in the capital Taipei. + +In 2010, use of the EasyCard was extended beyond transportation. Card holders +can now pay in all major convenience stores and major retail companies like +Starbucks or even SOGO. + +However, the system is still using the MIFARE Classic RFID transponder +technology, whose very limited security-by-obscurity proprietary encryption +system (CRYPTO1) has been broken years ago. + +This document analyzes the results of combining the practical attacks +on the MIFARE Classic CRYPTO1 system in the context of the EasyCard payment +system. +\end{abstract} + +\tableofcontents + +\section{Foreword} + +This document is the result of my personal research on the EasyCard +system. It was done out of my personal interest in security research +on information technology. No competitor of the EasyCard corporation, +or other business or political stakeholder ever encouraged, supported or +funded this work in any way. + +The result of this research is presented to the general public in the +hope it will make people re-consider the amount of trust they place +in proprietary systems that provide no evidence of their security, +and no option for the general public or the scientific community to +validate it. + +This paper is also directed at the legislator and the regulatory authorities, +in the hope that it will help them to produce better rules and requirements on +the technology designed for and usedby operators of security relevant systems +such as banking. + +\section{Introducing the EasyCard} + +FIXME + +\section{Published security research on MIFARE Classic} + +FIXME + +\section{Published tools for MIFARE Classic attacks} + +FIXME + +\section{Analyzing the EasyCard} + +A new, genuine EasyCard was obtained from one of the EasyCard vending machines +in a Taipei MRT station. + +As it is public knowledge that the EasyCard system is based on MIFARE +technology, any MIFARE-compatible RFID reader (PCD, Proximity Coupling Device) +can be used to establish a physical communications link according to ISO +14443-1 and -2, as well as performing the anti-collision procedure according +to ISO 14443-3. + +The author has used the OpenPCD RFID reader to do this, and has confirmed that +the EasyCard in fact is a card with ISO 14443-3 compatible anti-collision +procedure. The ATQA response also looks like that of a standard MIFARE Classic +transponder. + +\subsection{Attempting to use standard keys} + +As some users of MIFARE Classic systems only use some sectors of a card, but +not all, an attempt was made to authenticate to any of the blocks using the +manufacturer-programmed standard keys. However, none of the card sectors were +using those standard keys. + +This also means that we could not use the key recovery method described in +FIXME, where keys of all other sectors are recovered based on the knowledge of +they key of at least one different sector. + +\subsection{Recovering the MIFARE CRYPTO1 keys} + +Since none of the sector keys was known, the publicly available MFCUK (MiFare +Classic Universal toolKit) implementation of the "Dark Side" attack (Nicolas T. +Courtois) was used as a card-only attack. + +All that was required was the MFCUK Free Software, as well as a RFID +reader as supported by libnfc. Compatible readers are widely available, +among them one for EUR 30 from http://www.touchatag.com/e-store. + +Using the MFCUK key recovery tool, the A and B keys for all sectors have +been recovered within FIXME. This attack can definitely be optimized +by using special-purpose hardware such as the Proxmark, which gives +hard-realtime control over the communication with the EasyCard. + +Furthermore, the key recovery can be optimized based on known-plaintext that is +common to all cards. + +\subsection{Dumping the content of the EasyCard} + +Once the sector keys have all been recovered, the full content of the EasyCard +can be dumped using any RFID reader supporting MIFARE Classic. The author +chose to use the same reader that was used for the MFCUK key recovery combined +with the nfc-mfclassic program (part of libnfc). + +A full dump of the newly-purchased, unused EasyCard revealed the following +content: + +0000000 a193 c031 88c3 0004 ba46 1214 1051 1004 +0000010 140e 0100 0207 0308 0409 1008 0000 0000 +0000020 0000 0000 0000 0000 0000 0000 0000 0000 +0000030 211a ccd0 f399 7708 008f 6ac6 53bf cf08 +0000040 ff02 0300 0000 059f 804c c926 0171 3601 +0000050 0000 1000 1027 0027 64de 0001 0000 bb00 +0000060 f1d6 b4e8 0012 0000 0000 6400 0064 6900 +0000070 2e64 f724 bd57 7708 008f 8917 3d48 5dcd +0000080 0190 0000 fe6f ffff 0190 0000 ff00 ff00 +0000090 0190 0000 fe6f ffff 0190 0000 ff00 ff00 +00000a0 0000 0000 0000 0000 0000 0000 0000 0000 +00000b0 0d3d 782b 33cd 7708 008f 2411 4ce7 ea3f +00000c0 0001 0005 0000 0000 0000 0000 0000 0000 +00000d0 0000 0000 0000 0000 0000 0000 0000 0000 +00000e0 0000 0000 0000 0000 0000 0000 0000 0000 +00000f0 2fb1 511f 85b4 7708 008f 8dc8 eef5 2850 +0000100 0000 0000 0000 0000 0000 0000 0000 0000 +0000110 0000 0000 0000 0000 0000 0000 0000 0000 +0000120 0000 0000 0000 0000 0000 0000 0000 0000 +0000130 4587 96bd 1f22 7708 008f 47ce 7619 1558 +0000140 0000 0000 0000 0000 0000 0000 0000 0000 +0000150 0000 0000 0000 0000 0000 0000 0000 0000 +0000160 0000 0000 0000 0000 0000 0000 0000 0000 +0000170 5583 7616 749e 7708 008f 9bf3 c129 8eb6 +0000180 0c00 0400 0044 0000 0000 0000 0000 4c00 +0000190 0200 2200 0022 0000 0000 0000 0200 0000 +00001a0 0000 0005 0000 0000 0000 0000 0000 0000 +00001b0 af5f 6aeb 3a2c 7708 008f c039 7a1d d248 +00001c0 0000 0000 0000 0000 0000 0000 0000 0000 +00001d0 0000 0000 0000 0000 0000 0000 0000 0000 +00001e0 0000 0000 0000 0000 0000 0000 0000 0000 +00001f0 aebf 906e f2bd 7708 008f e3e7 988f aaaa +0000200 0000 0000 0000 0000 0000 0000 0000 0000 +0000210 0000 0000 0000 0000 0000 0000 0000 0000 +0000220 0000 0000 0000 0000 0000 0000 0000 0000 +0000230 ec9f 8bc6 4b89 7708 008f 53b0 2571 9e66 +0000240 0000 0000 0000 0000 0000 0000 0000 0000 +0000250 0000 0000 0000 0000 0000 0000 0000 0000 +0000260 0000 0000 0000 0000 0000 0000 0000 0000 +0000270 edc5 c17c 8a36 7708 008f 9a58 b6d9 5a8b +0000280 0000 0000 0000 0000 0000 0000 0000 0000 +0000290 0000 0000 0000 0000 0000 0000 0000 0000 +00002a0 0000 0000 0000 0000 0000 0000 0000 0000 +00002b0 40f7 60bf 4b8a 7708 008f 3a00 c93a 63e8 +00002c0 0000 0000 0000 0000 0000 0000 0000 0000 +00002d0 0000 0000 0000 0000 0000 0000 0000 0000 +00002e0 0000 0000 0000 0000 0000 0000 0000 0000 +00002f0 b50a 9f96 d2e3 7708 008f 4855 7cdb 7dff +0000300 0000 0000 0000 0000 0000 0000 0000 0000 +0000310 0000 0000 0000 0000 0000 0000 0000 0000 +0000320 0000 0000 0000 0000 0000 0000 0000 0000 +0000330 4c06 3ebc e595 7708 008f 9a5b 001b d14a +0000340 0000 0000 0000 0000 0000 0000 0000 0000 +0000350 0000 0000 0000 0000 0000 0000 0000 0000 +0000360 0000 0000 0000 0000 0000 0000 0000 0000 +0000370 3fb0 45ce 6f6b 7708 008f c0bf adb0 d662 +0000380 0000 0000 0000 0000 0000 0000 0000 0000 +0000390 0000 0000 0000 0000 0000 0000 0000 0000 +00003a0 0000 0000 0000 0000 0000 0000 0000 0000 +00003b0 3320 9074 e84c 7708 008f 0094 85d5 7aaa +00003c0 8000 c926 0071 0000 0000 0000 0064 0064 +00003d0 0000 0000 0000 0000 0000 0000 0000 0000 +00003e0 0000 0000 0000 0000 0000 0000 0000 0000 +00003f0 ea02 0bda b62a 7708 008f 0000 0000 0000 + +\subsection{Re-engineering the on-card data format} + +When the author started his research, there was no pre-existing public +knowledge on the data format used by the EasyCard system. As such, +significant time was spent analyzing it. + +The card was subsequently used to perform a number of transactions such as +use of public transportation and purchase of goods in stores. + +After each transaction, again a full dump of the card contents was made, +and the difference to the previous dump analyzed carefully. No particular +tools have been used for analysis. Most of the work relied on hex-dumps +of the card content and using the {\tt diff} utility to visualize differences +between two consecutive versions. + +During the analysis, it was quickly revealed that there are four +distinctive sets of changes that can be associated with a transaction: +\begin{itemize} +\item The card balance, stored as MIFARE value block +\item The transaction log +\item The transaction log index +\item The last MRT entry/exit record +\end{itemize} + +Furthermore, a constant header has been identified. It was never changed during +any of the tested transactions. + +The result of this analysis can be found in the next section: + +\section{Re-engineered EasyCard Data Format} + +\subsubsection{Sector 0 and 1: The header} +\subsubsection{Sector 2: The card balance as value block} + +The first two blocks of Sector 3 store the current remaining debit account +balance as a MIFARE Classic VALUE BLOCK. The format of this block is +documented in the official NXP vendor documentation on the MIFARE chip +used inside the card. + +The value block is decremented every time payment is made with the card. + +Given the MIFARE access bits, it is assumed that the RFID readers in public +transportation as well as stores use key A for this sector, as key A is +sufficient to read and decrement the VALUE block. + +Re-charging the card must happen using authentication with key B, as only +Key B has permissions to increment and/or write to this sector. + +\subsubsection{Sectors 3 through 5: The transaction log} + +Every time a transaction is made with the card, an entry in the transaction log +on the card itself is generated. Every entry occupies one full 16-byte block. + +The structure of a transaction log entry is as follows: +\begin{itemize} +\item 1 byte Transaction ID +\item 4 bytes Timestamp +\item 1 byte Transaction type +\item 2 bytes Cost charged for transaction +\item 2 bytes Remaining balance after transaction +\item 1 byte MRT Station ID +\item 1 byte Unknown +\item 2 bytes RFID Reader ID +\item 2 bytes Unknown +\end{itemize} + +The {\em Transaction ID} is a monotonically increasing value, incrementing with +each transaction. + +The {\em Timestamp} is a 32bit value in the standard UNIX time() format (Seconds +since January 1st 1970 00:00:00). However, it does not reference UTC but CST. + +The {\em Transaction type} indicates the type of transaction. Following codes +are known: +\begin{itemize} +\item {\tt 0x00} Entering MRT station +\item {\tt 0x11} Leaving MRT station +\item {\tt 0x80} Re-entering (connecting) MRT station +\item {\tt 0x20} Purchase of goods in shop +\end{itemize} + +The {\em Cost} and {\em Remaining balance} fields are unsigned 16bit integer +values representing the price in NTD (New Taiwan Dollars). + +In case of a MRT related transaction, the {\em MRT Station ID} encodes the MRT +station at which the transaction was performed. By visiting the TRTC (Taiwan +Rapid Transport Corporation) website, one can see the same numeric identifiers +being used within the URLs that link from the MRT map to the per-station web +pages. As such, a full table of MRT station names and corresponding +identifiers has been compiled and implemented as part of {\tt easytool}. + +The {\em RFID Reader ID} is presumed to be a unique identifer for the specific +RFID Terminal. Subsequent transactions at the same terminal will render +the same number in this field. + +\subsubsection{The transaction log pointer} + +\subsubsection{Sector 7: The last MRT entry/exit record} + +Block 2 (Offset 0x1e0) contains a record dscribing the last MRT station +that was entered using this EasyCard. +\begin{itemize} +\item Bytes 0...3 are unknown +\item Byte 4 contains the MRT station code +\item Bytes 6...8 are unknown +\item Bytes 9...12 contain the Timestamp +\item Bytes 13..15 are unknown +\end{itemize} + +Block 1 (Offset 0xd0) of the same sector contains a record using the same +structure. However, this record describes the last MRT station that was +left using this EasyCard. + +It is assumed that this information is used by the system to compute both the +distance (and thus fee) to be paid by the current ride, as well as any +applicable discount in case a connection is made from MRT into a bus. + +\section{Manipulating the EasyCard} + +\section{Mistakes of the EasyCard Corporation} + +\subsection{Deploying old technology} + +The Taipei Smart Card corporation (predecessor to the EasyCard Company) was +established in 2000, and it took until June 2002 to deploy the first EasyCard +system. + +The underlying Mifare Classic product was launched in 1994, and thus already +relatively old and outdated technology at that time. + +It was publicly documented by NXP that the security of the system is baesd on a +{\em prorprietary, symmetric, 48bit cipher}. Symmetric 48-bit encryption +was definitely no longer state-of-the-art in the year 2000. At that time, +the popular web-browser Netscape Navigator (used e.g. for web-based online +banking) had already introduced support for symmetric 128bit ciphers. + +\subsection{Deploying proprietary security technology} + +There are two concepts of achieving security in any system: {\em Security by +design} and {\em Security by obscurity}. + +In the former systems, security is achieved by using well-designed systems +that have undergone public peer review and have been subject to cryptanalysis. +As a result, the system is secure because it has undergond the review and +scrutiny of the international community of cryptographers and security experts. + +So, despite making all details of the system, particularly the cryptographic +algorithms open, an attacker is not able to circumvent the systems security. + +A system relying on {\em Security by obscurity} is only secure because +nobody knows the details of how it works. As soon as this information +has either leaked or recovered e.g. using reverse engineering techniques, +the system is broken. + +FIXME: Link to Bruce Schneier + +\subsection{Not reacting to academic research in the field} + +Starting in 2007, researchers have published a variety of attacks on +the CRYPTO-1 cipher and MIFARE Classic system. For a list of related +publications, see the bibliography of this paper. + +\subsection{Not reacting to public availability of MIFARE attack tools} + +Following-up the scientific publications, tools implementing practical +attacks on MIFARE Classic have been developed and published. Such +tools implement a variety of attacks, including card-only key-recovery +attacks. + +\subsection{No upgrade to more secure cards as they become available} + +In the same year the EasyCard was first deployed (2002), the supplier of the +MIFARE Classic system has already been shipping a much more secure system +called DESfire. The improvements include: 112-bit key length, and the use +of the internationally verified and audited DES algorithm in its 3DES variant. + +Despite its availability for 8 years since 2002, the EasyCard corporation has +apparently never updated their system to a more secure card like the DESfire +card. + +Based on the authors experience with the RFID card market, the price difference +of DESfire compared to MIFARE Classic has been on the order of USD 1 per card +from 2006 on. + +So, in order to save USD 1 per each issued card, the EasyCard corporation has +artificially kept down the security level of their system, not catching +up with state-of-the-art commercially available technology. + +\subsection{Extending EasyCard to generic payment outside public transport} + +The security of any system always has to be analyzed in the context of the +threat model, i.e. what can an attacker gain from compromising the system. + +As the key derivation of the EasyCard is not (yet?) broken, it is thus +currently not possible to completely manufacture forged cards. However, +technically, cards can be re-charged without making actual payment for it. + +As far as cards are only used for public transportation, the incentive +for fraudulent use is relatively small and contained. Also, the amount +of money for each transaction is realtively small. + +Thus, while the author would still disagree, it might be the case that +the business risk analysis inside EasyCard Corporation would have deemed the +risk of fraud in the public transport sector as acceptable. + +When such a card is used as an electronic payment system in stores where +goods of much higher value can be purcased, the threat model is quite +different, though. + +The 2010 introduction of the EasyCard as means of payment in retail +stores - while still relying on known-broken, 16 year old technology - +can thus only be seen as ignorant and incompetent. + +It does not help that EasyCard corporation has to provide a full refund +and keep all deposits in a bank trust. It also doesn't help that fraudulent +use is detected using analysis of the transaction data long after it happened. + +EasyCard fraud is simple to perform and will inevitably happen. Somebody +has to pay for the losses incurred due to fraud. Even if such losses +only reflect themselves in increased transaction fees for retail stores, in the +end it will be the consumer who pays them indirectly due to higher prices +including such fees. + +\section{Proposed Changes / Improvements} + +The author of this paper argues that use of the current EasyCard system +should immediately be restricted to payment for public transportation, +and the decision to authorize it as form of payment in retail stores +as of April 1st, 2010 reverted. + +A new system, based on state-of-the-art technology and algorithms +and the {\em Security by Design} principle should be developed. Such +a system should go through independent, open academic review. + +The approval of such a system, or technical security requirements for +such a system should not be within EasyCard itself, but should be +made by a regulatory authority, consulted by independent technical experts +in the field. + +A changing roll-over to the new system can be made by starting to issue +the new cards using a more secure RFID system whenever new EasyCards are +bought. Whenever a consumer wants to re-charge their card, the old MIFARE +Classic based card should be retracted and a new, more secure card be issued. +Existing EasyCards can be circulated in the system for a grace period. + +Depending on the technical details of the existing deployed RFID +reader/terminal base in public transportation and retail stores, either +a software-only update is sufficient or replacement hardware has to be +introduced. + +EasyCard corporation should be liable for the complete system +upgrade/transition cost, as the fault of the system can only be blamed +on them. + +\section{Bibliography} +%1. [WPMCC09] - "Wirelessly Pickpocketing a Mifare Classic Card" +%2. [ESO08] - "2008-esorics.pdf" +%3. [ESOSL08] - "2008-esorics-slides-updated.pdf" +%4. [KON08] - "2008-koning-thesis.pdf" +%5. [VER08] - "2008-verdult-thesis.pdf" +%6. [PATMC] - "A Practical Attack on the MIFARE Classic.pdf" +%7. [NCOURFIDSEC09] - "mifare_courtois_rfidsec09.pdf" +%8. [MFCLTRB09] - "MifareClassicTroubles.ppt" +%9. [TEEP08] - "p2008-teepe-classic_mistakes.pdf" +%10. [RFIDSANJ] - "RFID Attacks_WCA_San_Jose.pdf" +%11. [ROSS] - "rossum-mifare.pdf" +%12. [PLOTZ08] - "SAR-PR-2008-21_.pdf" +%13. [ROSSSASG] - "SASG35_Peter_v_Rossum_Mifare.pdf" +%14. [DARK2009] - "THE DARK SIDE OF SECURITY BY OBSCURITY and Cloning MiFare Classic Rail and Building Passes, Anywhere, Anytime" + +\end{document} |