Cryptography Pitfalls at Geekfest

Transcript

1. Cryptography Pitfalls John Downey | @jtdowney @jtdowney 1
2. @jtdowney 2
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4. The views expressed in this presentation are my own, and not those of PayPal or any of its affiliates. @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 number generators 3. Not using random data when it is required @jtdowney 18
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21. Pitfalls 1. Not using a cryptographically strong random number generator 2. Broken 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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30. Pitfalls 1. Not using a cryptographically strong random number generator 2. Broken random number generators 3. Not using random data when it is required @jtdowney 30
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32. Recommendations • Use a cryptographically strong random number generator • Unix-like • Read from /dev/urandom • Windows • RandomNumberGenerator in System.Security.Cryptography (.NET) • CryptGenRandom (Windows) @jtdowney 32
33. Hash Functions @jtdowney 33
34. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 34
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39. 9EC4C12949A4F31474F299058CE2B22A @jtdowney 39
40. 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 40
41. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 41
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43. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 43
44. Message Authentication Code (MAC) tag = MAC(key, value) • Takes: • key - shared secret • value - value to protected integrity of • Returns: • tag - value that represents the integrity @jtdowney 44
45. Naive approach tag = sha256(key || value) @jtdowney 45
46. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = sha256(secret + value) @jtdowney 46
47. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1<garbage>actually make that at $0" signature = sha256(secret + value) @jtdowney 47
48. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = hmac_sha256(secret, value) @jtdowney 48
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51. 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 51
52. Password Storage @jtdowney 52
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61. sha1(password) @jtdowney 61
62. 1. One-way • Value can be used for verification @jtdowney 62
63. sha1(salt + password) @jtdowney 63
64. 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 64
65. Hash functions are fast @jtdowney 65
66. 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 66
67. Adaptive Hashing bcrypt, scrypt, argon2, or PBKDF2 @jtdowney 67
68. Recommendations • Delegate authentication if possible • Facebook, Twitter, Google, Github • Store one-way verifiers using bcrypt, scrypt, argon2, or PBDKF2 @jtdowney 68
69. So your password storage is bad @jtdowney 69
70. It will be ok, you can fix it @jtdowney 70
71. Example: password_hash column is sha1(salt || password) @jtdowney 71
72. • 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 • This does require the previous password scheme wasn't atrociously bad (e.g. DES crypt) @jtdowney 72
73. Now: password_hash column is bcrypt(sha1(salt || password)) @jtdowney 73
74. Ciphers @jtdowney 74
75. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 75
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79. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 79
80. 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 80
81. ECB Encrypt while (remaining blocks) { block = ... # next 16 byte (128 bit chunk) ouput.append(AES_Encrypt(key, block)) } @jtdowney 81
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84. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 84
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89. World of hurt @jtdowney 89
90. Recommendations • Prefer to use box/secret box from NaCL/libsodium • Stop using DES • Stop building your own on top of AES • Stop encrypting without protecting integrity @jtdowney 90
91. 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 91
92. TLS/SSL @jtdowney 92
93. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library @jtdowney 93
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96. Hostname verification • Check that you got the certificate for who you intended to connect to • Hostname verification is protocol dependent • OpenSSL doesn't have it built in @jtdowney 96
97. $ curl -k https://example.com or curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0); curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0); @jtdowney 97
98. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library @jtdowney 98
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100. SSL Labs https://www.ssllabs.com @jtdowney 100
101. TLS Server Settings https://mozilla.github.io/server-side-tls/ssl-config-generator/ @jtdowney 101
102. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library @jtdowney 102
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105. 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 105
106. Trust @jtdowney 106
107. 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 107
108. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ 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 108
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110. Certificate Pinning @jtdowney 110
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112. Recommendations • Think about what organizations you really trust • Investigate certificate pinning for your apps @jtdowney 112
113. Quantum Computers @jtdowney 113
114. Pitfalls 1. Assuming current crypto will last forever @jtdowney 114
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117. Recommendations • Follow the PQCrypto discussion • Stay away from PQCrypto until the industry starts to standardize • Hope that researchers are moving fast enough @jtdowney 117
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119. Stanford Crypto Class http://crypto-class.com @jtdowney 119
120. Matasano Crypto Challenges http://cryptopals.com @jtdowney 120
121. Questions John Downey | @jtdowney @jtdowney 121
122. 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 • https://flic.kr/p/AV1Nd @jtdowney 122