Cryptography Pitfalls at BsidesMSP 2017

Transcript

1. Cryptography Pitfalls John Downey | @jtdowney @jtdowney 1
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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
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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, SSH, or VPN/IPsec • For data at rest • Use GnuPG • Data to be signed • Use GnuPG @jtdowney 13
14. • 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 14
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16. Random Number Generation @jtdowney 16
17. 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 17
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20. 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 20
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22. 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 22
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27. MD_Update(&m,buf,j); @jtdowney 27
28. Don't add uninitialised data to the random number generator. This stop valgrind from giving error messages in unrelated code. (Closes: #363516) @jtdowney 28
29. /* 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 29
30. 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 30
31. Hash Functions @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. 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 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. 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 42
43. Naive approach tag = sha256(key + value) @jtdowney 43
44. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = sha256(secret + value) @jtdowney 44
45. Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" + " or $0" signature = sha256(secret + value) @jtdowney 45
46. Fixed secret = "my-secret-key" value = "buy 10 units at $1" signature = hmac_sha256(secret, value) @jtdowney 46
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49. 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 49
50. Ciphers @jtdowney 50
51. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 51
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55. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 55
56. 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 56
57. ECB Encrypt while (remaining blocks) { block = ... # next 16 byte (128 bit chunk) ouput.append(AES_Encrypt(key, block)) } @jtdowney 57
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60. Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 60
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65. World of hurt @jtdowney 65
66. 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 66
67. 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 67
68. TLS/SSL @jtdowney 68
69. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library @jtdowney 69
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74. Hostname verification @jtdowney 74
75. 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 75
76. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library @jtdowney 76
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78. SSL Labs https://www.ssllabs.com @jtdowney 78
79. testssl.sh https://testssl.sh @jtdowney 79
80. TLS Server Settings https://mozilla.github.io/server-side-tls/ssl-config-generator/ @jtdowney 80
81. Pitfalls 1. Not verifying the certificate chain or hostname 2. Misconfigured server settings 3. Using a broken library @jtdowney 81
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84. 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 84
85. Trust @jtdowney 85
86. 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 86
87. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ 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 87
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89. Certificate Pinning @jtdowney 89
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91. Recommendations • Think about what organizations you really trust • Investigate certificate pinning for your apps @jtdowney 91
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93. Stanford Crypto Class http://crypto-class.com @jtdowney 93
94. Matasano Crypto Challenges http://cryptopals.com @jtdowney 94
95. Questions John Downey | @jtdowney @jtdowney 95
96. Bonus Round @jtdowney 96
97. Quantum Computers @jtdowney 97
98. Pitfalls 1. Assuming current crypto will last forever @jtdowney 98
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101. Recommendations • Follow the PQCrypto discussion • Stay away from PQCrypto until the industry starts to standardize • Hope that researchers are moving fast enough @jtdowney 101
102. 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 102