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Tamper evident encryption of integers using keyed Hash Message Authentication Code Brad Baker November 16, 2009 UCCS 11/16/2009Brad Baker - Master's Project Report1 Master’s Project Report

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Agenda 11/16/2009Brad Baker - Master's Project Report2 Introduction / Motivation Background Design Analysis Implementation Testing Conclusion / Future Work References

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Section 1: Introduction 11/16/2009Brad Baker - Master's Project Report3

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Introduction 11/16/2009Brad Baker - Master's Project Report4 Confidentiality and integrity of data are important features in a database environment [16, 26] Integrity is also referred to as tamper detection for this project Database tampering is defined as loss of relationship between sensitive data and other data in the record Standard solutions exist including [16]: Symmetric and asymmetric encryption for confidentiality Message authentication codes and hash digests for integrity Standard solutions require end-user to build a complex process combining hash and encryption functions This project presents the “HMAC based Tamper Evident Encryption” scheme (HTEE) as an alternative solution HMAC is Hashed Message Authentication Code

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Motivation 11/16/2009Brad Baker - Master's Project Report5 Create an efficient and simple-use tamper evident encryption technique Single step, single column tamper detection Focus on processing numeric data in a database system Improve performance of the encryption operation compared to standard approaches Improve on previous work that introduced an HMAC based encryption/decryption process Investigate uses of HMAC as an encryption and key generation function

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Related Work 11/16/2009Brad Baker - Master's Project Report6 File system and application level integrity [21, 22] Checksums, CRC, RAID Parity, Cryptographic file systems OpenSSL, Intrusion detection, Tripwire, Samhain Forensic analysis and tamper detection [23] Notarization with hash function and reliance on audit log Analysis of how and when data was tampered Parallel encryption and authentication code [24, 25] Various implementations of encryption combined with MAC Original HMAC encryption scheme [1] Integer encryption with HMAC Foundation for HTEE tamper detection

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Comparison of Solutions 11/16/2009Brad Baker - Master's Project Report7 Solutions for integrity and confidentiality considered: HTEE: Encryption and tamper detection with HMAC function AES & SHA-1: Encryption and hash, detects tampering AES: Encryption, detects random changes only Each provides a unique benefit: Solution Encryption Strength Tamper Detection Simple Usage Encrypt Efficiency Decrypt Efficiency HTEEMedium/High*Yes FastSlow AES & SHA-1HighYesNoModerate AESHighNoYesModerate * Security of the HTEE scheme is variable and relies on the hash algorithm used.

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Section 2: Background 11/16/2009Brad Baker - Master's Project Report8

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Background - HMAC 11/16/2009Brad Baker - Master's Project Report9 HMAC – keyed Hash Message Authentication Code [13] Produces a secure authentication code (digest) using message and secret key, providing integrity and authenticity Proposed in [3], and standardized as FIPS PUB 198 [12] Unauthorized individual cannot generate digest without key Can use any underlying hash function, MD5, SHA-1, etc. Function generates two keys from secret key The HMAC process is: HMAC(key, msg) = Hash((key XOR opad) || Hash ((key XOR ipad) || msg) Where opad=“0x5c5c…” and ipad=“0x3636…”

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Background – Integer Encryption 11/16/2009Brad Baker - Master's Project Report10 Integer encryption with HMAC Original HMAC integer encryption scheme proposed in [1] The scheme operates on integer plaintext values, decomposed into two components or buckets Encryption is performed with HMAC calculation, decryption is performed with exhaustive search The scheme is inefficient on encryption and for large integers Encryption is recursive HMAC rather than direct calculation Two buckets results in a large search ranges for decryption A detailed analysis including testing results are available in [2] HTEE is based on this scheme, and improves upon it

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Original HMAC process 11/16/2009Brad Baker - Master's Project Report11

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Introductory Example 11/16/2009Brad Baker - Master's Project Report12 Original HMAC example: Plaintext integer value 567,212 and bucket size 5,000 Bucket 1 = 113, Bucket 2 = 2212 Plaintext can be retrieved as (567,212 = 113*5, ) HMAC digest / ciphertext output: 113 becomes “fG7Agfw4OErQw+IX2iBw853LBKg=“ 2212 becomes “YOLpnTHGIHurCvkrgczFMM1C5PI=“ Decryption searches through 5,000 values to find a ciphertext match for each bucket

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Section 3: Design 11/16/2009Brad Baker - Master's Project Report13

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HTEE Design 11/16/2009Brad Baker - Master's Project Report14 Processes positive integer values Decomposition of plaintext into multiple buckets of size 1,000 For example: 2,412,345,678 becomes four buckets: Bucket 1 = 2; Bucket 2 = 412; Bucket 3 = 345; Bucket 4 = 678; In the original scheme, a 50,000 bucket size would make two buckets: Bucket 1 = 48246; Bucket 2 = 45678; Key transformation based on a unique value related to plaintext Each encryption operation uses a different key Encryption keys depend on original key and unique related data The unique value is any data that must remain the same in relation to the plaintext, for example: Record’s primary key, other unique data, hash digest of unique data

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HTEE Design 11/16/2009Brad Baker - Master's Project Report15 Encryption operation: Calculate HMAC digest for each bucket Decryption operation: Search for digest match between ciphertext and all values (0-999) Tamper detection: Decryption operation cannot find matching value Two key transformation functions used: element and bucket Element transformation creates a key for each plaintext HMAC executed recursively four times with unique value and original key Bucket transformation creates key for each bucket value HMAC executed iteratively with ciphertext output and original key Encryption performed with transformed keys, not original key

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HTEE Design 11/16/2009Brad Baker - Master's Project Report16 HMAC digests for all buckets in a plaintext are concatenated to form ciphertext Decryption follows key generation process, plus an exhaustive search for ciphertext match. No match indicates data was tampered with, that the ciphertext or unique related data have changed The HTEE process is: HTEE(Plaintext, Key, Unique) = HMAC(Bucket1, f Key (Key, Unique)) || HMAC(Bucket2, f Key (Key, Unique)) || … Bucket N Where {f Key } is key transformation (element and bucket) and Bucket 1 through Bucket N are decomposed from Plaintext

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Example of HTEE 11/16/2009Brad Baker - Master's Project Report17 Record contents (DATA value is sensitive, must be encrypted): ID = 1001; DATA = After decomposition of DATA value: bucket1 = 654; bucket2 = 321 Original Key, 512 bit: fwWe6MNL5WC9gRgCfVbUsuFLeX8IfwKbnkWmlKhj5Tx2Ods+VkmKS73AeFt0EsXy+zmfWEsyOEaKSx/oYMSmRA== Generated keys for buckets (dependent on ID value and original key): Bucket1 key: qi5K5JmBNRfOuPf8qQvgPVVZ5nHZjlgoDb8un4GS/NxFhbRNdnE5B80kPe3rpqIvHRDzdZsiEmpk+2Ozcb5yXg== Bucket2 key: ylT5vKaGkdc1XMtW0z+HOb1Td2eqLkrkmYE1F8649/ypC+A9VVnmcdmOWCgNvy6fgZL83EWFtE12cTkHzSQ97Q== Ciphertext result from HMAC (bucket, key): Bucket1 cipher: Ziuytd9t8Vn1h5ldqZjv57sTe2k= Bucket2 cipher: uk/ACtScX2oxJUPyEPdPWSPCXQk= Final Ciphertext: Ziuytd9t8Vn1h5ldqZjv57sTe2k=uk/ACtScX2oxJUPyEPdPWSPCXQk= Final Output: ID = 1001; CIPHER = Ziuytd9t8Vn1h5ldqZjv57sTe2k=uk/ACtScX2oxJUPyEPdPWSPCXQk=

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HTEE Encryption Concept 11/16/2009Brad Baker - Master's Project Report18

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Element Key Transformation [3, 4, 9, 11] 11/16/2009Brad Baker - Master's Project Report19

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Bucket Key Transformation 11/16/2009Brad Baker - Master's Project Report20

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Section 4: Analysis 11/16/2009Brad Baker - Master's Project Report21

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Security Analysis 11/16/2009Brad Baker - Master's Project Report22 Cryptographic strength of HTEE is based on HMAC Key transformation and encryption use HMAC function Cryptographic strength of HMAC is based on underlying hash function [3, 4, 5] For this project, SHA-1 is used as underlying hash Hash can be changed for additional security of HMAC [3] HMAC proven secure from forgery if hash compression operation is a pseudo-random function [4, 7, 11] HMAC is not susceptible to hash collision attacks that affect MD5 and SHA-1 [3, 4, 5] Collisions are still produced but more difficult to attack

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Security Analysis 11/16/2009Brad Baker - Master's Project Report23 HMAC can be attacked by forgery or key recovery attacks [3, 6] Key recovery attacks typically have chosen or known plaintext The birthday paradox controls probability to find an HMAC collision [3, 5, 11, 15] For SHA-1, 2 80 (message, digest) pairs from HMAC are needed Research shows key recovery attacks that are better than brute force, but still worse than birthday attack [6, 7, 10] For the HTEE scheme key recovery attacks are the primary concern Forgeries are less of a concern as they could only break a single record’s tamper detection capability

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Security Analysis 11/16/2009Brad Baker - Master's Project Report24 The layering of key generation in HTEE makes analysis difficult: Attacker knows the unique value and final digest/ciphertext Given the digest it is difficult to find the key or message value Given the unique value, it is difficult to obtain original key Consider general form: HTEE(P,K,U) = HMAC(P, f K (K,U)) Intermediate keys and plaintexts are masked and HMAC is difficult to break if using an effective underlying hash HMAC operation protects plaintext and intermediate key, makes derivation of original key more difficult A key recovery attack will take over 2 80 message pairs Most applications will not use the same secret key for a large number of records (over 2 40, appx. 1 trillion) This is short of the required over 2 80 pairs needed for key recovery

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Tamper Detection Analysis 11/16/2009Brad Baker - Master's Project Report25 HTEE creates a distinct key sequence based on the unique value related to plaintext Identical keys only occur on hash collisions This is improbable unless a very large number of records are processed If ciphertext or unique value are changed then the key sequence or HMAC output will differ Tamper detection will only fail if the original and changed HTEE process produce a collision Probability of collision for each bucket is appx. 3.42x Based on the birthday attack with1,000 values [15, 16] Probability is{P = 1 – e (-k^2/2N) } with {k = 1000} and {N = }

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Section 5: Implementation 11/16/2009Brad Baker - Master's Project Report26

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Implementation 11/16/2009Brad Baker - Master's Project Report27 HTEE process implemented as a PostgreSQL add-on and a command line program Built in the C language Microsoft Visual C Express Edition PostgreSQL server versions and Implemented versions: Command line program used for validation and flat file processing PostgreSQL add-on is considered the primary implementation Two functions added to PostgreSQL server: Encryption: htee_enc(plaintext, unique value) Decryption: htee_dec(ciphertext, unique value) Simple operation, example SQL for encryption: SELECT htee_enc(data,unique) FROM test Maximum of six buckets or 9x10 17 integer value supported

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Implementation 11/16/2009Brad Baker - Master's Project Report28 SHA-1 used for underlying hash function Specifies use of 512 bit key, blocks of 160 bit ciphertext output Input key is 88 base64 characters, output is 28 base64 characters per bucket value Ciphertext output for six buckets is 168 bytes of base64 encoded data Comparable AES output is 116 bytes, HTEE is a 44% increase Compared to plaintext data, a 21-fold increase Several challenges encountered: Extending PostgreSQL in Windows environment Interfacing with the PostgreSQL backend

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Section 6: Testing 11/16/2009Brad Baker - Master's Project Report29

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Testing 11/16/2009Brad Baker - Master's Project Report30 Compared three methods for encryption: Basic AES (aes1): Does not provide tamper detection AES & unique value (aes2): Provides tamper detection HTEE scheme: Provides tamper detection Tested six datasets, 20,000 random integers in each Each dataset with different number of buckets, one through six Results verified tamper detection with AES2 and HTEE methods HTEE on average was four times faster on encryption but four times slower on decryption than AES

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Performance comparison 11/16/2009Brad Baker - Master's Project Report31

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HTEE performance details 11/16/2009Brad Baker - Master's Project Report32

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Performance analysis 11/16/2009Brad Baker - Master's Project Report33 The performance of HTEE and the original scheme [1] are compared with algorithmic analysis HTEE is significantly more efficient on encryption, and decryption for large numbers [2] Original scheme increases with n 0.5, HTEE increases with log 1000 (n) Testing verifies that HTEE is much faster for similar datasets The large bucket size required for two buckets becomes prohibitively expensive to calculate decryption Encryption SchemeRelative complexity HTEE Encryption2*log 1000 (n) Constant HTEE Decryption1001*log 1000 (n) Constant Original Encryption2*n 0.5 Polynomial Original Decryption2*n 0.5 Polynomial

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Section 7: Conclusion 11/16/2009Brad Baker - Master's Project Report34

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Lessons Learned 11/16/2009Brad Baker - Master's Project Report35 Encountered and solved implementation challenges Null bytes, memory management, hash processing PostgreSQL extension in Windows environment Interfacing with PostgreSQL backend, operating on data types Challenges in algorithm design Properly protecting key information in the transformation process Adapting key transformation for a database environment Created custom key generation for random 512 bit keys OpenSSL package proved difficult to generate simple random strings Effect of implementation on security Processing time exposing information about plaintext values Effect of small input values Can be mitigated by expanding the size of the unique value

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Conclusion 11/16/2009Brad Baker - Master's Project Report36 HTEE provides strong tamper detection and data integrity Ciphertext and other related data are tied together HTEE provides strong confidentiality Security based on the underlying HMAC and hash functions Can be improved with stronger hash functions For regulatory requirements recommend AES encryption HTEE is more efficient on encryption and less efficient on decryption than AES Ideal for encryption-heavy applications where tamper detection is needed Examples include archival and auditing systems, including financial information Additional information available:

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Future Work 11/16/2009Brad Baker - Master's Project Report37 Plaintext value range: HTEE scheme is limited to positive integer values Future work can expand operation to negative values, floating point values, or ASCII encoded data Floating point can be encoded with multiplication by a positive factor of 10, the factor must be stored in the ciphertext data Security Proof A conceptual analysis of cryptographic strength is presented Future work can prove of the security of HTEE, focused on: HMAC as a pseudo-random function Effect of unique value and bucket values on HMAC randomness

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Questions? 11/16/2009Brad Baker - Master's Project Report38

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References 11/16/2009Brad Baker - Master's Project Report39 1. Dong Hyeok Lee; You Jin Song; Sung Min Lee; Taek Yong Nam; Jong Su Jang, "How to Construct a New Encryption Scheme Supporting Range Queries on Encrypted Database," Convergence Information Technology, International Conference on, vol., no., pp , Nov URI: 2. Brad Baker, "Analysis of an HMAC Based Database Encryption Scheme," UCCS Summer 2009 Independent study July URI: 3. Mihir Bellare; Ran Canetti; Hugo Krawczyk; “Keying Hash Functions for Message Authentication”, IACR Crypto 1996 URI: 4. Mihir Bellare, “New Proofs for NMAC and HMAC: Security without Collision-Resistance,” IACR Crypto 2006 URI: 5. Mihir Bellare, “Attacks on SHA-1,” 2005 URI: 6. Pierre-Alain Fouque; Gaëtan Leurent; Phong Q. Nguyen, "Full Key-Recovery Attacks on HMAC/NMAC-MD4 and NMAC-MD5," IACR Crypto 2007 URI: ftp://ftp.di.ens.fr/pub/users/pnguyen/Crypto07.pdfftp://ftp.di.ens.fr/pub/users/pnguyen/Crypto07.pdf 7. Scott Contini; Yiqun Lisa Yin, “Forgery and Partial Key-Recovery Attacks on HMAC and NMAC using Hash Collisions (Extended Version),” 2006 URI:

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References 11/16/2009Brad Baker - Master's Project Report40 8. Hyrum Mills; Chris Soghoian; Jon Stone; Malene Wang, “NMAC: Security Proof,” 2004 URI: 9. Ran Canetti, “The HMAC construction: A decade later,” 2007 URI: 10. Yu Sasaki, “A Full Key Recovery Attack on HMAC-AURORA-512,” 2009 URI: 11. Jongsung Kim; Alex Biryukov; Bart Preneel; and Seokhie Hong, “On the Security of HMAC and NMAC Based on HAVAL, MD4, MD5, SHA-0 and SHA-1”, 2006 URI: 12. NIST, March FIPS Pub 198 HMAC specification. URI = 13. Wikipedia, October HMAC reference material. URI= 14. Wikipedia, October SHA-1 reference material. URI=

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References 11/16/2009Brad Baker - Master's Project Report Wikipedia, October Birthday Attack reference. URI= 16. Forouzan, Behrouz A Cryptography and Network Security. McGraw Hill higher Education. ISBN Simon Josefsson, GPL implementation of HMAC-SHA1. URI= 18. Scott G. Miller, GPL implementation of SHA-1 hash. URI= Bob Trower, August Open source base64 encoding implementation, adapted for test program. URI= 20. PostgreSQL, October Server Documentation. URI= 21. Gopalan Sivathanu; Charles P. Wright; and Erez Zadok, “Ensuring data integrity in storage: techniques and applications,” Workshop On Storage Security And Survivability, Nov URI =

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References 11/16/2009Brad Baker - Master's Project Report Vishal Kher; Yongdae Kim, “Securing Distributed Storage: Challenges, Techniques, and Systems” Workshop On Storage Security And Survivability, Nov URI = 23. Kyriacos Pavlou; Richard Snodgrass, “Forensic Analysis of Database Tampering,” ACM Transactions on Database Systems (TODS), 2008 URI = 24. Elbaz, R.; Torres, L.; Sassatelli, G.; Guillemin, P.; Bardouillet, M.; Rigaud, J.B., "How to Add the Integrity Checking Capability to Block Encryption Algorithms," Research in Microelectronics and Electronics 2006, Ph. D., vol., no., pp , URI: 25. Elbaz, R.; Torres, L.; Sassatelli, G.; Guillemin, P.; Bardouillet, M., "PE-ICE: Parallelized Encryption and Integrity Checking Engine," Design and Diagnostics of Electronic Circuits and systems, 2006 IEEE, vol., no., pp , URI: 26. Wikipedia, October Information Security Reference. URI=

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