Cryptography Pitfalls at Little Rock Tech Fest 2015

Transcript

1. Cryptography Pitfalls John Downey | @jtdowney @jtdowney 1
2. @jtdowney 2
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4. Chicago @jtdowney 4
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6. Confidentiality @jtdowney 6
7. Authentication @jtdowney 7
8. Identification @jtdowney 8
9. Rigorous Science @jtdowney 9
10. Peer Review @jtdowney 10
11. @jtdowney 11
12. 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 12
13. • For data in transit • Use TLS (née SSL), SSH, or VPN/IPsec • For data at rest • Use GnuPG @jtdowney 13
14. • Avoid low level libraries • OpenSSL • PyCrypto • Bouncy Castle • Use a high level library • NaCL/libsodium (C, Ruby, etc) • Keyczar (Python and Java) @jtdowney 14
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16. Random Number Generation @jtdowney 16
17. • Randomness is a central part of any crypto system • Used to generate: • Encryption keys • API keys • Session tokens • Password reset tokens @jtdowney 17
18. Pitfalls 1. Not using a cryptographically strong random number generator 2. Broken random random number generators 3. Not using random data when it is required @jtdowney 18
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21. Pitfalls 1. Not using the right random number generator 2. Broken random random number generators 3. Not using random data when it is required @jtdowney 21
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23. MD_Update(&m,buf,j); @jtdowney 23
24. Don't add uninitialised data to the random number generator. This stop valgrind from giving error messages in unrelated code. (Closes: #363516) @jtdowney 24
25. /* 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 25
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27. Pitfalls 1. Not using the right random number generator 2. Broken random random number generators 3. Not using random data when it is required @jtdowney 27
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29. Recommendations • Unix-like • Read from /dev/urandom • Windows • RandomNumberGenerator.Create() (.NET) • CryptGenRandom (Windows) @jtdowney 29
30. Hash Functions @jtdowney 30
31. • Often called a fingerprint • One way • Not reversible (can’t find person without fingerprint DB) • Ideally, no two people with same fingerprint (no two inputs) @jtdowney 31
32. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 32
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37. 9EC4C12949A4F31474F299058CE2B22A @jtdowney 37
38. 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 38
39. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 39
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41. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 41
42. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = sha256(secret + "|" + value) @jtdowney 42
43. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1<garbage>actually make that at $0" signature = sha256(secret + "|" + value) @jtdowney 43
44. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = hmac_sha256(secret, value) @jtdowney 44
45. Message Authentication Code (MAC) tag = hmac_sha256(key, value) • key - shared secret • value - value to protected integrity of • tag - value that represents the integrity @jtdowney 45
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47. Recommendations • Use SHA-256 (SHA-2 family) • Choose HMAC-SHA-256 if you want a signature • Stop using MD5 • Don't use SHA-1 in new projects • Phase it out for uses that require collision resistance @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. So your password storage is bad @jtdowney 63
64. It will be ok, you can fix it @jtdowney 64
65. Example: password_hash column is sha1(salt || password) @jtdowney 65
66. • Don't wait for user to login and silently upgrade • Wrap bcrypt around existing scheme • Use bcrypt(sha1(salt || password) • Upgrade all passwords in place @jtdowney 66
67. Now: password_hash column is bcrypt(sha1(salt || password)) @jtdowney 67
68. Block Ciphers @jtdowney 68
69. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode 3. Not using authenticated encryption @jtdowney 69
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71. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode 3. Not using authenticated encryption @jtdowney 71
72. AES - primitive 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 72
73. ECB Encrypt while (remaining blocks) { block = ... # next 16 byte (128 bit chunk) ouput.append(AES_Encrypt(key, block)) } @jtdowney 73
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76. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode 3. Not using authenticated encryption @jtdowney 76
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78. World of hurt @jtdowney 78
79. Recommendations • Prefer to use box/secret box from NaCL/libsodium • Stop using DES • Stop building your own on top of AES @jtdowney 79
80. What if you have to use AES • Do not use ECB mode • Be sure to use authenticated encryption: • GCM mode would be a good first choice • Verify the tag/MAC first • Still easy to mess up in a critical way @jtdowney 80
81. Stream Ciphers @jtdowney 81
82. XOR Refresher @jtdowney 82
83. XOR Refresher A xor 0 = A A xor A = 0 A xor B = C A xor C = B B xor C = A A xor A xor B = B @jtdowney 83
84. Encrypting keystream = expand(key) # => "\x84\x859\x87\xBC\x15\x91\x01N\xD4^\xA0\xAC371" message = 'attack at dawn' ciphertext = message xor keystream # => "\xE5\xF1M\xE6\xDF~\xB1`:\xF4:\xC1\xDB]" @jtdowney 84
85. Decrypting keystream = expand(key) # => "\x84\x859\x87\xBC\x15\x91\x01N\xD4^\xA0\xAC371" message = ciphertext xor keystream # => 'attack at dawn' @jtdowney 85
86. Pitfalls 1. Using old/weak algorithms 2. Reusing the same key 3. Not using authenticated encryption @jtdowney 86
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89. Pitfalls 1. Using old/weak algorithms 2. Reusing the same key 3. Not using authenticated encryption @jtdowney 89
90. keystream = expand(key) message1 = 'attack at dawn' ciphertext1 = message1 xor keystream message2 = 'attack at dusk' ciphertext2 = message2 xor keystream @jtdowney 90
91. (ciphertext1) xor (ciphertext2) ! ! (message1 xor keystream) xor (message2 xor keystream) @jtdowney 91
92. message1 xor keystream xor message2 xor keystream @jtdowney 92
93. message1 xor message2 @jtdowney 93
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95. Pitfalls 1. Using old/weak algorithms 2. Reusing the same key 3. Not using authenticated encryption @jtdowney 95
96. General 1 keystream = expand(key) message = 'attack at dawn' ciphertext = message xor keystream @jtdowney 96
97. Spy tweak = "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x14\x04\x05" new_ciphertext = message xor tweak @jtdowney 97
98. General 2 keystream = expand(key) message = new_ciphertext xor keystream message = 'attack at dusk' @jtdowney 98
99. General 2 message = (new_ciphertext) xor keystream ! message = (ciphertext xor tweak) xor keystream @jtdowney 99
100. General 2 'attack at dawn' xor tweak 'attack at dusk' @jtdowney 100
101. Recommendations • Use box/secret box from NaCL/libsodium • Stop using RC4 • Ensure you don't reuse keys • This means reusing nonces as well • Always protect ciphertext integrity (i.e. with a MAC) @jtdowney 101
102. TLS/SSL Verification @jtdowney 102
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104. Pitfalls 1. Not verifying the certificate chain 2. Not verifying the hostname 3. Using a broken library @jtdowney 104
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106. $ curl -k https://example.com or curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); @jtdowney 106
107. Pitfalls 1. Not verifying the certificate chain 2. Not verifying the hostname 3. Using a broken library @jtdowney 107
108. • Hostname verification is protocol dependent • OpenSSL doesn't have it built in • Also, some people just turn it off: curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0); @jtdowney 108
109. Pitfalls 1. Not verifying the certificate chain 2. Not verifying the hostname 3. Using a broken library @jtdowney 109
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112. 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 (badssl.com) @jtdowney 112
113. TLS Server Settings https://mozilla.github.io/server-side-tls/ssl-config-generator/ @jtdowney 113
114. Trust @jtdowney 114
115. 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 115
116. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ 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 116
117. 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 117
118. Certificate Pinning @jtdowney 118
119. Recommendations • Think about what organizations you really trust • Investigate certificate pinning for your apps @jtdowney 119
120. @jtdowney 120
121. Stanford Crypto Class https://www.coursera.org/course/crypto @jtdowney 121
122. Matasano Crypto Challenges http://cryptopals.com @jtdowney 122
123. Questions John Downey | @jtdowney @jtdowney 123
124. Images • https://flic.kr/p/6eagaw • https://flic.kr/p/4KWhKn • https://flic.kr/p/9F2BCv • https://flic.kr/p/486xYS • https://flic.kr/p/7Ffppm • https://flic.kr/p/8TuJD9 • https://flic.kr/p/4iLJZt • https://flic.kr/p/4pGZuz • https://flic.kr/p/48w7wP • https://flic.kr/p/8aZWNE • https://flic.kr/p/5NRHp • https://flic.kr/p/7p7raq • https://flic.kr/p/aZEE1Z • https://flic.kr/p/7WtwAz • https://flic.kr/p/6AN9mM • https://flic.kr/p/6dt62u • https://flic.kr/p/4ZqwyB • https://flic.kr/p/Bqewr • https://flic.kr/p/ecdhVE @jtdowney 124