Cryptography Pitfalls at Chicago Coder Conference

Transcript

1. Cryptography Pitfalls John Downey | @jtdowney @jtdowney 1
2. @jtdowney 2
3. @jtdowney 3
4. Confidentiality @jtdowney 4
5. Authentication @jtdowney 5
6. Identification @jtdowney 6
7. Rigorous Science @jtdowney 7
8. Peer Review @jtdowney 8
9. @jtdowney 9
10. You have probably seen the door to a bank vault, at least in the movies. You know, 10-inch-thick, hardened steel, with huge bolts to lock it in place. It certainly looks impressive. We often find the digital equivalent of such a vault door installed in a tent. The people standing around it are arguing over how thick the door should be, rather than spending their time looking at the tent. -Cryptography Engineering by Niels Ferguson, Bruce Schneier, and Tadayoshi Kohno @jtdowney 10
11. • For data in transit • Use TLS/SSL, SSH, or VPN/IPsec • For data at rest • Use GnuPG • Use a high level library • NaCL/libsodium (C, Ruby, etc) • Keyczar (Python and Java) @jtdowney 11
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13. Random Number Generation @jtdowney 13
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17. MD_Update(&m,buf,j); @jtdowney 17
18. Don't add uninitialised data to the random number generator. This stop valgrind from giving error messages in unrelated code. (Closes: #363516) @jtdowney 18
19. /* DO NOT REMOVE THE FOLLOWING CALL TO MD_Update()! */ MD_Update(&m,buf,j); /* We know that line may cause programs such as purify and valgrind to complain about use of uninitialized data. The problem is not, it's with the caller. Removing that line will make sure you get really bad randomness and thereby other problems such as very insecure keys. */ @jtdowney 19
20. @jtdowney 20
21. Recommendations • Unix-like • Use /dev/urandom • Never ending file you read from • Each read is more random data • Wrappers • SecureRandom (Ruby) • SecureRandom.getInstance("NativePRNG") (Java) • Windows • RandomNumberGenerator.Create() (.NET) • CryptGenRandom (.NET / Windows) @jtdowney 21
22. Length Extension Attacks @jtdowney 22
23. Hash Functions @jtdowney 23
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25. 9EC4C12949A4F31474F299058CE2B22A @jtdowney 25
26. mission = """ USCYBERCOM plans, coordinates, integrates, synchronizes and conducts activities to: direct the operations and defense of specified Department of Defense information networks and; prepare to, and when directed, conduct full spectrum military cyberspace operations in order to enable actions in all domains, ensure US/Allied freedom of action in cyberspace and deny the same to our adversaries. """ md5(mission) # => 9EC4C12949A4F31474F299058CE2B22A @jtdowney 26
27. Recommendations • Use SHA-256 (SHA-2 family) • Stop using MD5 • Don't use SHA-1 in new projects • Remember fingerprints are not authentication • Someone can recompute the hash without knowing any secret @jtdowney 27
28. Length Extension Attacks @jtdowney 28
29. RestClient.post( "https://example.com/things", name: 'Widget', price: 1_23, signature: signature ) @jtdowney 29
30. signature = sha1("api-key|name=Widget&price=123") # => 8CBBCB204861672F93B26A6401E685195AB5719B @jtdowney 30
31. Internal State @jtdowney 31
32. Initial State h0 = 0x67452301 h1 = 0xEFCDAB89 h2 = 0x98BADCFE h3 = 0x10325476 h4 = 0xC3D2E1F0 @jtdowney 32
33. Merkle–Damgård construction 1. Take block (64 bytes) 2. Run "compression" function (updates h0-h4) 3. Repeat on next block @jtdowney 33
34. End State h0 = 0x8CBBCB20 h1 = 0x4861672F h2 = 0x93B26A64 h3 = 0x01E68519 h4 = 0x5AB5719B 8CBBCB20 | 4861672F | 93B26A64 | 01E68519 | 5AB5719B @jtdowney 34
35. &price=0 @jtdowney 35
36. api-key|name=Widget&price=123&price=0 @jtdowney 36
37. signature = sha1("api-key|name=Widget&price=123&price=0") # => 7CA17A2B91BD35C09D50A3AD5CAD1E9B396DDEF4 @jtdowney 37
38. RestClient.post( "https://example.com/things", name: 'Widget', price: 0, signature: signature ) @jtdowney 38
39. Recommendations • Use HMAC-SHA-256 for similar cases • Message Authentication Code • HMAC / Keyed hash function • Resistant to length extension attacks @jtdowney 39
40. ECB Mode @jtdowney 40
41. Block Ciphers @jtdowney 41
42. AES ciphertext = AES_Encrypt(key, plaintext) plaintext = AES_Decrypt(key, ciphertext) • Function over: • key - 128, 192, or 256 bit value • plaintext - 128 bit value • ciphertext - 128 bit value @jtdowney 42
43. ECB Encrypt while (remaining blocks) { block = ... # next 64 byte (128 bit chunk) ouput.append(AES_Encrypt(key, block)) } @jtdowney 43
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46. Recommendations • Prefer to use "secret box" from libsodium/NaCl • Stop using DES • Stop building your own ontop of AES @jtdowney 46
47. What if you have to use AES • Do not use ECB mode • Be sure to use authenticated encryption: • GCM, CCM, OCB mode • CBC/CTR with an HMAC of IV and ciphertext • Verify the tag/MAC first • Still easy to break in a critical way @jtdowney 47
48. Password Storage @jtdowney 48
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55. sha1(password) @jtdowney 55
56. 1. One-way • Value can be used for verification @jtdowney 56
57. sha1(salt + password) @jtdowney 57
58. 1. One-way • Value can be used for verification 2. Randomized • Can largely defeat pre-computed tables • Forces attackers to focus on one password @jtdowney 58
59. Hash functions are fast @jtdowney 59
60. 1. One-way • Value can be used for verification 2. Randomized • Can largely defeat pre-computed tables • Forces attackers to focus on one password 3. Slow @jtdowney 60
61. Adaptive Hashing bcrypt, scrypt, or PBKDF2 @jtdowney 61
62. Recommendations • Delegate authentication if possible • Facebook, Twitter, Google, Github • Store one-way verifiers using bcrypt, scrypt, or PBDKF2 @jtdowney 62
63. TLS/SSL Verification @jtdowney 63
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65. 1. Verify the certificate chain to a trusted root (VERIFY_PEER) 1. Follow chain of trust 2. Check all of the signatures 3. Validate certificate parameters 2. Verify hostname of server (not always done for you) @jtdowney 65
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70. Recommendations • Do ensure you're validating connections • Lean on a framework/library if possible • But check that it also does the right thing • Setup and automated test to validate this setting @jtdowney 70
71. Trust @jtdowney 71
72. The authenticity of host 'apollo.local (10.0.2.56)' can't be established. RSA key fingerprint is 04:63:c1:ba:c7:31:04:12:14:ff:b6:c4:32:cf:44:ec. Are you sure you want to continue connecting (yes/no)? @jtdowney 72
73. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that the RSA host key has just been changed. The fingerprint for the RSA key sent by the remote host is 04:63:c1:ba:c7:31:04:12:14:ff:b6:c4:32:cf:44:ec. Please contact your system administrator. @jtdowney 73
74. AOL Time Warner Inc. AS Sertifitseerimiskeskus AddTrust Baltimore beTRUSTed Buypass CNNIC COMODO CA Limited Certplus certSIGN Chambersign Chunghwa Telecom Co., Ltd. ComSign Comodo CA Limited Cybertrust, Inc Deutsche Telekom AG Deutscher Sparkassen Verlag GmbH Dhimyotis DigiCert Inc DigiNotar Digital Signature Trust Co. Disig a.s. EBG Bilişim Teknolojileri ve Hizmetleri A.Ş. EDICOM Entrust, Inc. Equifax GTE Corporation GeoTrust Inc. GlobalSign nv-sa Hongkong Post Japan Certification Services, Inc. Japanese Government Microsec Ltd. NetLock Halozatbiztonsagi Kft. Network Solutions L.L.C. PM/SGDN QuoVadis Limited RSA Security Inc SECOM Trust Systems CO.,LTD. SecureTrust Corporation Sociedad Cameral de Certificación Digital Sonera Staat der Nederlanden Starfield Technologies, Inc. StartCom Ltd. SwissSign AG Swisscom TC TrustCenter GmbH TDC Taiwan Government Thawte The Go Daddy Group, Inc. The USERTRUST Network TÜBİTAK TÜRKTRUST Unizeto Sp. z o.o. VISA ValiCert, Inc. VeriSign, Inc. WISeKey Wells Fargo XRamp Security Services Inc @jtdowney 74
75. Certificate Pinning @jtdowney 75
76. Recommendations • Think about what organizations you really trust • Consider disabling some roots • Use certificate pinning in your apps @jtdowney 76
77. Stanford Crypto Class https://www.coursera.org/course/crypto @jtdowney 77
78. Matasano Crypto Challenges http://cryptopals.com @jtdowney 78
79. Questions @jtdowney 79
80. Images • https://flic.kr/p/4KWhKn • https://flic.kr/p/9F2BCv • https://flic.kr/p/486xYS • https://flic.kr/p/7Ffppm • https://flic.kr/p/4iLJZt • https://flic.kr/p/4pGZuz • https://flic.kr/p/8aZWNE • https://flic.kr/p/5NRHp • https://flic.kr/p/7p7raq • https://flic.kr/p/aZEE1Z • https://flic.kr/p/6AN9mM • https://flic.kr/p/6jCNY3 • https://flic.kr/p/6dt62u • https://flic.kr/p/7WtwAz • https://flic.kr/p/4ZqwyB • https://flic.kr/p/Bqewr • https://flic.kr/p/ecdhVE @jtdowney 80