Cryptography Pitfalls at BSidesPhilly 2016

Transcript

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

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2. Chicago
   @jtdowney 2
   

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3. @jtdowney 3
   

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4. @jtdowney 4
   

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5. The views expressed in this
   presentation are my own, and not
   those of PayPal or any of its
   affiliates.
   @jtdowney 5
   

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6. @jtdowney 6
   

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7. Confidentiality
   @jtdowney 7
   

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8. Authentication
   @jtdowney 8
   

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9. Identification
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10. Rigorous Science
    @jtdowney 10
    

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11. Peer Review
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12. @jtdowney 12
    

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13. 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 13
    

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14. • For data in transit
    • Use TLS (née SSL), SSH, or VPN/IPsec
    • For data at rest
    • Use GnuPG
    • Data to be signed
    • Use GnuPG
    @jtdowney 14
    

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15. • Avoid low level libraries
    • OpenSSL
    • PyCrypto
    • Bouncy Castle
    • Use a high level library
    • NaCL/libsodium (C, Ruby, etc)
    • Keyczar (Python and Java)
    @jtdowney 15
    

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16. @jtdowney 16
    

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17. Random Number
    Generation
    @jtdowney 17
    

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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
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19. @jtdowney 19
    

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20. @jtdowney 20
    

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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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22. @jtdowney 22
    

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23. @jtdowney 23
    

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24. MD_Update(&m,buf,j);
    @jtdowney 24
    

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25. Don't add uninitialised data to
    the random number generator.
    This stop valgrind from giving
    error messages in unrelated code.
    (Closes: #363516)
    @jtdowney 25
    

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26. /* 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 26
    

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27. @jtdowney 27
    

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28. @jtdowney 28
    

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29. @jtdowney 29
    

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30. @jtdowney 30
    

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31. 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 31
    

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32. @jtdowney 32
    

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33. Recommendations
    • Use a cryptographically strong random number generator
    • Unix-like
    • Read from /dev/urandom
    • Windows
    • RandomNumberGenerator in
    System.Security.Cryptography (.NET)
    • CryptGenRandom (Windows)
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34. Hash Functions
    @jtdowney 34
    

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35. Pitfalls
    1. Using weak/old algorithms
    2. Misunderstanding checksums
    3. Length extension attacks
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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. @jtdowney 39
    

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40. 9EC4C12949A4F31474F299058CE2B22A
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41. 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 41
    

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42. Pitfalls
    1. Using weak/old algorithms
    2. Misunderstanding checksums
    3. Length extension attacks
    @jtdowney 42
    

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43. @jtdowney 43
    

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44. Pitfalls
    1. Using weak/old algorithms
    2. Misunderstanding checksums
    3. Length extension attacks
    @jtdowney 44
    

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45. 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
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46. Naive approach
    tag = sha256(key || value)
    @jtdowney 46
    

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47. Length Extension Attacks
    secret = "my-secret-key"
    value = "buy 10 units at $1"
    signature = sha256(secret + value)
    @jtdowney 47
    

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48. Length Extension Attacks
    secret = "my-secret-key"
    value = "buy 10 units at $1actually make that at $0"
    signature = sha256(secret + value)
    @jtdowney 48
    

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49. Length Extension Attacks
    secret = "my-secret-key"
    value = "buy 10 units at $1"
    signature = hmac_sha256(secret, value)
    @jtdowney 49
    

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50. @jtdowney 50
    

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51. @jtdowney 51
    

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52. 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 52
    

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53. Password Storage
    @jtdowney 53
    

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54. Don't wait to fix your password
    storage
    • http://www.bsidesphilly.org/2016/12/cryptography_pitfalls/
    • https://jtdowney.com/blog/2015/11/01/dont-wait-to-fix-
    your-password-storage/
    @jtdowney 54
    

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55. Ciphers
    @jtdowney 55
    

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56. Pitfalls
    1. Using old/weak algorithms
    2. Using ECB mode for block ciphers
    3. Not using authenticated encryption
    @jtdowney 56
    

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57. @jtdowney 57
    

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58. @jtdowney 58
    

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59. @jtdowney 59
    

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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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61. 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 61
    

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62. ECB Encrypt
    while (remaining blocks) {
    block = ... # next 16 byte (128 bit chunk)
    ouput.append(AES_Encrypt(key, block))
    }
    @jtdowney 62
    

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63. @jtdowney 63
    

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64. @jtdowney 64
    

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65. Pitfalls
    1. Using old/weak algorithms
    2. Using ECB mode for block ciphers
    3. Not using authenticated encryption
    @jtdowney 65
    

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66. @jtdowney 66
    

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67. @jtdowney 67
    

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68. @jtdowney 68
    

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69. @jtdowney 69
    

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70. World of hurt
    @jtdowney 70
    

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71. 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 71
    

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72. 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 72
    

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73. TLS/SSL
    @jtdowney 73
    

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74. Pitfalls
    1. Not verifying the certificate chain or hostname
    2. Misconfigured server settings
    3. Using a broken library
    @jtdowney 74
    

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75. @jtdowney 75
    

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76. @jtdowney 76
    

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77. @jtdowney 77
    

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78. Hostname verification
    @jtdowney 78
    

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79. 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 79
    

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80. Pitfalls
    1. Not verifying the certificate chain or hostname
    2. Misconfigured server settings
    3. Using a broken library
    @jtdowney 80
    

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81. @jtdowney 81
    

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82. SSL Labs
    https://www.ssllabs.com
    @jtdowney 82
    

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83. testssl.sh
    https://testssl.sh
    @jtdowney 83
    

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84. TLS Server Settings
    https://mozilla.github.io/server-side-tls/ssl-config-generator/
    @jtdowney 84
    

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85. Pitfalls
    1. Not verifying the certificate chain or hostname
    2. Misconfigured server settings
    3. Using a broken library
    @jtdowney 85
    

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86. @jtdowney 86
    

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87. @jtdowney 87
    

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88. 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 88
    

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89. Trust
    @jtdowney 89
    

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90. 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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91. @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
    @ 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 91
    

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92. @jtdowney 92
    

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93. Certificate Pinning
    @jtdowney 93
    

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94. @jtdowney 94
    

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95. Recommendations
    • Think about what organizations you really trust
    • Investigate certificate pinning for your apps
    @jtdowney 95
    

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96. Quantum Computers
    @jtdowney 96
    

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97. Pitfalls
    1. Assuming current crypto will last forever
    @jtdowney 97
    

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98. @jtdowney 98
    

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99. @jtdowney 99
    

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100. Recommendations
     • Follow the PQCrypto discussion
     • Stay away from PQCrypto until the industry starts to
     standardize
     • Hope that researchers are moving fast enough
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101. @jtdowney 101
     

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102. Stanford Crypto Class
     http://crypto-class.com
     @jtdowney 102
     

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103. Matasano Crypto Challenges
     http://cryptopals.com
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104. Questions
     John Downey | @jtdowney
     @jtdowney 104
     

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105. Images
     • https://flic.kr/p/6eagaw
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     • https://flic.kr/p/AV1Nd
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