Cryptography Pitfalls at GOTO Chicago 2016

Transcript

1. Cryptography Pitfalls
   John Downey | @jtdowney
   @jtdowney 1
   

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2. @jtdowney 2
   

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3. Chicago
   @jtdowney 3
   

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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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5. @jtdowney 5
   

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6. Confidentiality
   @jtdowney 6
   

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7. Authentication
   @jtdowney 7
   

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8. Identification
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9. Rigorous Science
   @jtdowney 9
   

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10. Peer Review
    @jtdowney 10
    

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11. @jtdowney 11
    

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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
    

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13. • For data in transit
    • Use TLS (née SSL), SSH, or VPN/IPsec
    • For data at rest
    • Use GnuPG
    @jtdowney 13
    

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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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15. @jtdowney 15
    

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16. Random Number
    Generation
    @jtdowney 16
    

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17. • Randomness is a central part of any crypto system
    • Used to generate:
    • Encryption keys
    • API keys
    • Session tokens
    • Password reset tokens
    @jtdowney 17
    

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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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19. @jtdowney 19
    

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20. @jtdowney 20
    

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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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22. @jtdowney 22
    

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23. MD_Update(&m,buf,j);
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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
    

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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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26. @jtdowney 26
    

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27. @jtdowney 27
    

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28. @jtdowney 28
    

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29. 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 29
    

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30. @jtdowney 30
    

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31. Recommendations
    • Unix-like
    • Read from /dev/urandom
    • Windows
    • RandomNumberGenerator.Create() (.NET)
    • CryptGenRandom (Windows)
    @jtdowney 31
    

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32. Hash Functions
    @jtdowney 32
    

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33. • 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)
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34. Pitfalls
    1. Using weak/old algorithms
    2. Misunderstanding checksums
    3. Length extension attacks
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35. @jtdowney 35
    

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36. @jtdowney 36
    

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37. @jtdowney 37
    

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38. @jtdowney 38
    

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39. 9EC4C12949A4F31474F299058CE2B22A
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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
    

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41. Pitfalls
    1. Using weak/old algorithms
    2. Misunderstanding checksums
    3. Length extension attacks
    @jtdowney 41
    

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42. @jtdowney 42
    

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43. Pitfalls
    1. Using weak/old algorithms
    2. Misunderstanding checksums
    3. Length extension attacks
    @jtdowney 43
    

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44. Length Extension Attacks
    secret = "my-secret-key"
    value = "buy 10 units at $1"
    signature = sha256(secret + "|" + value)
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45. Length Extension Attacks
    secret = "my-secret-key"
    value = "buy 10 units at $1actually make that at $0"
    signature = sha256(secret + "|" + value)
    @jtdowney 45
    

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46. Length Extension Attacks
    secret = "my-secret-key"
    value = "buy 10 units at $1"
    signature = hmac_sha256(secret, value)
    @jtdowney 46
    

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47. Message Authentication Code
    (MAC)
    tag = hmac_sha256(key, value)
    • key - shared secret
    • value - value to protected integrity of
    • tag - value that represents the integrity
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48. @jtdowney 48
    

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49. @jtdowney 49
    

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50. 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
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51. Password Storage
    @jtdowney 51
    

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52. @jtdowney 52
    

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53. @jtdowney 53
    

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54. @jtdowney 54
    

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55. @jtdowney 55
    

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56. @jtdowney 56
    

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57. @jtdowney 57
    

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58. sha1(password)
    @jtdowney 58
    

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59. 1. One-way
    • Value can be used for verification
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60. sha1(salt + password)
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61. 1. One-way
    • Value can be used for verification
    2. Randomized
    • Can largely defeat pre-computed tables
    • Forces attackers to focus on one password
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62. Hash functions are fast
    @jtdowney 62
    

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63. 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 63
    

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64. Adaptive Hashing
    bcrypt, scrypt, or PBKDF2
    @jtdowney 64
    

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65. Recommendations
    • Delegate authentication if possible
    • Facebook, Twitter, Google, Github
    • Store one-way verifiers using bcrypt, scrypt, or PBDKF2
    @jtdowney 65
    

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66. So your password
    storage is bad
    @jtdowney 66
    

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67. It will be ok,
    you can fix it
    @jtdowney 67
    

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68. Example:
    password_hash column is sha1(salt || password)
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69. • 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 you're previous password scheme wasn't
    atrociously bad (e.g. DES crypt)
    @jtdowney 69
    

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70. Now:
    password_hash column is bcrypt(sha1(salt || password))
    @jtdowney 70
    

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71. Ciphers
    @jtdowney 71
    

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72. Pitfalls
    1. Using old/weak algorithms
    2. Using ECB mode
    3. Not using authenticated encryption
    @jtdowney 72
    

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73. @jtdowney 73
    

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74. @jtdowney 74
    

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75. @jtdowney 75
    

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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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77. 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 77
    

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78. ECB Encrypt
    while (remaining blocks) {
    block = ... # next 16 byte (128 bit chunk)
    ouput.append(AES_Encrypt(key, block))
    }
    @jtdowney 78
    

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79. @jtdowney 79
    

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80. @jtdowney 80
    

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81. Pitfalls
    1. Using old/weak algorithms
    2. Using ECB mode
    3. Not using authenticated encryption
    @jtdowney 81
    

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82. @jtdowney 82
    

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83. @jtdowney 83
    

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84. @jtdowney 84
    

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85. @jtdowney 85
    

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86. World of hurt
    @jtdowney 86
    

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87. 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 87
    

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88. 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 88
    

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89. TLS/SSL Verification
    @jtdowney 89
    

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90. @jtdowney 90
    

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91. Pitfalls
    1. Not verifying the certificate chain
    2. Not verifying the hostname
    3. Using a broken library
    @jtdowney 91
    

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92. @jtdowney 92
    

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93. $ curl -k https://example.com
    or
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, 0);
    @jtdowney 93
    

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94. Pitfalls
    1. Not verifying the certificate chain
    2. Not verifying the hostname
    3. Using a broken library
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95. • 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 95
    

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96. Pitfalls
    1. Not verifying the certificate chain
    2. Not verifying the hostname
    3. Using a broken library
    @jtdowney 96
    

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97. @jtdowney 97
    

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98. @jtdowney 98
    

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99. 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)
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100. TLS Server Settings
     https://mozilla.github.io/server-side-tls/ssl-config-generator/
     @jtdowney 100
     

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101. Trust
     @jtdowney 101
     

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102. 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)?
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103. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
     @ 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.
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104. @jtdowney 104
     

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105. Certificate Pinning
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106. @jtdowney 106
     

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107. Recommendations
     • Think about what organizations you really trust
     • Investigate certificate pinning for your apps
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108. @jtdowney 108
     

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109. Stanford Crypto Class
     http://crypto-class.com
     @jtdowney 109
     

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110. Matasano Crypto Challenges
     http://cryptopals.com
     @jtdowney 110
     

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111. Questions
     John Downey | @jtdowney
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112. 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
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