Cryptography Pitfalls at CactusCon 2019

Transcript

1. Cryptography Pitfalls John Downey | @jtdowney @jtdowney 1
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3. The views expressed in this presentation are my own, and not those of PayPal or any of its affiliates. @jtdowney 3
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5. Confidentiality @jtdowney 5
6. Authentication @jtdowney 6
7. Identification @jtdowney 7
8. Rigorous Science @jtdowney 8
9. Peer Review @jtdowney 9
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11. 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 11
12. • For data in transit • Use TLS, SSH, or VPN/IPsec • For data at rest • Use GnuPG • Data to be signed • Use GnuPG @jtdowney 12
13. • Avoid low level libraries • OpenSSL • PyCrypto • Bouncy Castle • Use a high level library • NaCL/libsodium (C, Ruby, PHP, etc) • Keyczar (C++, Python, and Java) @jtdowney 13
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15. Random Number Generation @jtdowney 15
16. Pitfalls 1. Not using a cryptographically strong random number generator 2. Not using random data when it is required 3. Broken random number generators @jtdowney 16
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19. Pitfalls 1. Not using a cryptographically strong random number generator 2. Not using random data when it is required 3. Broken random number generators @jtdowney 19
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21. Pitfalls 1. Not using a cryptographically strong random number generator 2. Not using random data when it is required 3. Broken random number generators @jtdowney 21
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26. MD_Update(&m,buf,j); @jtdowney 26
27. Don't add uninitialised data to the random number generator. This stop valgrind from giving error messages in unrelated code. (Closes: #363516) @jtdowney 27
28. /* 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 28
29. Recommendations • Use a cryptographically strong random number generator • Unix-like • Read from /dev/urandom • Windows • RandomNumberGenerator in System.Security.Cryptography (.NET) • CryptGenRandom • Java use java.security.SecureRandom @jtdowney 29
30. Hash Functions @jtdowney 30
31. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 31
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36. 9EC4C12949A4F31474F299058CE2B22A @jtdowney 36
37. 9EC4C12949A4F31474F299058CE2B22A 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. @jtdowney 37
38. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 38
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40. Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 40
41. 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 41
42. Naive approach tag = sha256(key + value) @jtdowney 42
43. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = sha256(secret + value) @jtdowney 43
44. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" + " or $0" signature = sha256(secret + value) @jtdowney 44
45. Fixed secret = "my-secret-key" value = "buy 10 units at $1" signature = hmac_sha256(secret, value) @jtdowney 45
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48. Recommendations • Use SHA-256 (SHA-2 family) • Choose HMAC-SHA-256 if you want a signature • Use BLAKE2b if you need speed • Stop using MD5 • Stop using SHA1 @jtdowney 48
49. Ciphers @jtdowney 49
50. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 50
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54. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 54
55. 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 55
56. ECB Encrypt while (remaining blocks) { block = ... # next 16 byte (128 bit chunk) ouput.append(AES_Encrypt(key, block)) } @jtdowney 56
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59. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 59
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64. World of hurt @jtdowney 64
65. 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 65
66. 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 66
67. TLS/SSL @jtdowney 67
68. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library 4. Shipping your private key @jtdowney 68
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73. Hostname verification @jtdowney 73
74. 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 74
75. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library 4. Shipping your private key @jtdowney 75
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77. SSL Labs https://www.ssllabs.com @jtdowney 77
78. testssl.sh https://testssl.sh @jtdowney 78
79. TLS Server Settings https://mozilla.github.io/server-side-tls/ssl-config-generator/ @jtdowney 79
80. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library 4. Shipping your private key @jtdowney 80
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83. 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 83
84. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library 4. Shipping your private key @jtdowney 84
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86. Trust @jtdowney 86
87. 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 87
88. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ 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 88
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90. Certificate Pinning @jtdowney 90
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92. Recommendations • Think about what organizations you really trust • Investigate certificate pinning for your apps @jtdowney 92
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94. Stanford Crypto Class http://crypto-class.com @jtdowney 94
95. Matasano Crypto Challenges http://cryptopals.com @jtdowney 95
96. Questions John Downey | @jtdowney @jtdowney 96
97. Bonus Round @jtdowney 97
98. Quantum Computers @jtdowney 98
99. Pitfalls 1. Assuming current crypto will last forever @jtdowney 99
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102. Recommendations • Follow the PQCrypto discussion • Stay away from PQCrypto until the industry starts to standardize • Hope that researchers are moving fast enough @jtdowney 102
103. 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 • https://flic.kr/p/5tWgh4 @jtdowney 103