Understanding Security APIs - CrySyS Lab

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This key binding attack effectively reduced the CCA’s 3DES down to only twice as good as single DES, which was by then widely considered insufficient. Several attacks exploiting the key binding flaw are described in sections 7.3.6 and 7.3.7. The attack techniques and implementations in the last few sections were published at the “Cryptographic Hardware and Embedded Systems” workshop in Paris in 2001 [8], and later in IEEE Computer [9]. The CHES paper inspired Clulow to examine the PIN verification functionality of financial APIs more closely, and he discovered half a dozen significant new attacks, which he detailed in his MSc thesis “The Design and Analysis of Cryptographic APIs for Security Devices” [15]. 3.3.3 Decimalisation Table Attack In late 2002 the author and Clulow independently made the next significant advance in attack technology – the discovery of information leakage attacks. Clulow had discovered the problems an entire year earlier, but was unable to speak publicly about them until late 2002, when he gave seminars at RSA Europe, and the University of Cambridge. Early in the next year the author published details of the ‘decimalisation table attack’, and Clulow published his M.Sc. thesis. The decimalisation table attack (explained fully in section 7.3.10) exploited flexibility in IBM’s method for calculating customer PINs from PANs. Once the PAN was encrypted with a PIN derivation key, it still remained to convert the 64-bit binary block into a four digit PIN. A natural representation of the block to the programmers was hexadecimal, but this would have been confusing for customers, so IBM chose take the hexadecimal output, truncate it to the first four digits, then decimalise these using a lookup table, or ‘decimalisation table’, as shown in figure 3.3. Account Number 4556 2385 7753 2239 Encrypted Accno 3F7C 2201 00CA 8AB3 Shortened Enc Accno 3F7C 0123456789ABCDEF 0123456789012345 Decimalised PIN 3572 Figure 3.3: IBM 3624-Offset PIN Generation Method Originally the decimalisation table was a fixed input – integrated into the PIN generation and verification commands, but somehow it became parameterised, and by the time the VSM and CCA APIs were implemented, the decimalisation table was 28
an input that could be specified by the user. If a normal PIN verification command failed, it discounted a single possibility – the incorrect guess at the PIN. However, if the decimalisation table was modified, much more information could be learnt. For example, if the user entered a trial PIN of 0000, and a decimalisation table of all zeroes, with a single 1 in the 7 position – 0000000100000000 – then if the verification succeeded the user could deduce that the PIN did not contain the digit 7. Zielinski optimised the author’s original algorithm, revealing that PINs could be determined with an average of 15 guesses [10]. 3.4 Attacks on Modern APIs Many of today’s Security APIs have been discovered to be vulnerable to the same or similar techniques as those described in this chapter. However, there are some more modern API designs which bear less resemblance to those used in financial security applications. In particular, the main issues relating to the security of PKI hardware security modules are authorisation and trusted path. These issues have only very recently been explored, and there have been no concrete attacks published. Chapter 8 includes a discussion of the issues of authorisation and trusted path, and describes several hypothetical attacks. Finally, if the reader is already thoroughly familiar with the attacks described in this chapter, attention should be drawn to several brand new Security API attacks which have been outlined in section 7.3.12, which were developed by the author as a result of analysis of nCipher’s payShield API. 29
Page 1 and 2: Understanding Security APIs Michael
Page 3: Dedication To Philip Barnes, who co
Page 6 and 7: Understanding Security APIs Michael
Page 8 and 9: 4.3 Certification Authorities . . .
Page 10 and 11: 7.3.1 VSM Compatibles - XOR to Null
Page 12 and 13: Chapter 1 Introduction In today’s
Page 14 and 15: Whatever you intend to get out of t
Page 16 and 17: The aspects of the research relatin
Page 18 and 19: it spawned the development of contr
Page 20 and 21: 2.4 Key Dates Year Events 1960 Deve
Page 22 and 23: ciphertext into a four digit number
Page 24 and 25: service engineer). In order for the
Page 26 and 27: 3.3 Development of the Attack Toolk
Page 30 and 31: Chapter 4 Applications of Security
Page 32 and 33: Higher-level goals maybe to achieve
Page 34 and 35: VISA. It also permits end-to-end co
Page 36 and 37: There are three sorts of threat to
Page 38 and 39: control - and would typically be is
Page 40 and 41: Secure Computing Base (NGSCB), prev
Page 42 and 43: Chapter 5 The Security API Industry
Page 44 and 45: • Individuals, Customers, Clients
Page 46 and 47: 5.2.2 1990 to 2000 Year Events 1991
Page 48 and 49: 5.3 Summary of HSM Manufacturers 5.
Page 50 and 51: pose crypto platform market, and si
Page 52 and 53: 5.3.8 Baltimore http://www.baltimor
Page 54 and 55: The Trusted Computing Group will li
Page 56 and 57: available, but should be carefully
Page 58 and 59: Chapter 6 Hardware Security Modules
Page 60 and 61: an increasing concern as the device
Page 62 and 63: • Potting is nowadays one of the
Page 64 and 65: • Light Sensors can be coupled wi
Page 66 and 67: 6.2.1 Tamper-Evidence Hardware Secu
Page 68 and 69: 6.3 HSM Summary This section introd
Page 70 and 71: 6.3.3 nCipher nForce API nCore API
Page 72 and 73: 6.3.5 nCipher netHSM API nCore API
Page 74 and 75: 6.3.7 Thales RG7000 API Proprietary
Page 76 and 77: 6.3.9 Chrysalis-ITS Luna CA3 API PK
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Chapter 7 Analysis of Security APIs
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First Command: Key Part Import User
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achieve the same functionality as o
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Figure 7.5 shows a common key manag
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7.2 The Attacker’s Toolkit This s
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early HSMs actually used this techn
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PIN numbers are often stored in enc
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operating systems. Naively implemen
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The supervisor key switch is turned
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7.3.4 4758 CCA - Key Import Attack
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7.3.6 4758 CCA - 3DES Key Binding A
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Bank Home Bank Home Bank Home Test
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the number of operations the HSM wo
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Implementation Overview The DES cra
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7.3.8 4758 CCA - Weak Key Timing At
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which is a many-to-one mapping betw
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Digits Possibilities A AAAA(1) AB A
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No # Poss. pins Decimalisation tabl
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tables in a generic way will be har
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Security Officer 1 -> HSM : SM?IK 8
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in. Consider the example below, whi
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Indeed it now seems that many conve
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• Search Tools - such as PROLOG -
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\% these are the commands provided
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--------------------------SPASS-STA
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Problem Specification The API is sp
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UI Decisions Figure 7.23: The MIMse
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Figure 7.25: The MIMsearch ‘Watch
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2. If the Security API prevents cer
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it can be enabled and disabled, the
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• When the host machine sends dat
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8.2.5 Legacy Issues • Isolate you
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The Visa Security Module had a seri
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Class I Passive tokens, which prese
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Smartcards Figure 8.2: Chrysalis Lu
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link to the authorisation process f
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To minimise the risk of breach, eac
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When no privileged operations are r
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8.4.3 How Many Security Officers ar
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Chapter 9 The Future of Security AP
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e unable to assure themselves that
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9.4 The Bottom Line Whilst it is ex
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10.1 Roles and Responsibilities Sec
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Chapter 11 Glossary 4753 IBM Crypto
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PKCS#11 Public Key Cryptography Sta
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[14] J. Clulow, “On the Security
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[53] http://www.cl.cam.ac.uk/~rnc1/
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