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Cryptography Pitfalls John Downey | @jtdowney @jtdowney 1

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Chicago @jtdowney 2

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@jtdowney 3

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@jtdowney 4

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@jtdowney 5

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The views expressed in this presentation are my own, and not those of PayPal or any of its affiliates. @jtdowney 7

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@jtdowney 8

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Confidentiality @jtdowney 9

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Authentication @jtdowney 10

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Identification @jtdowney 11

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Rigorous Science @jtdowney 12

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Peer Review @jtdowney 13

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@jtdowney 14

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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 15

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• 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 16

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• Avoid low level libraries • OpenSSL • PyCrypto • Bouncy Castle • Use a high level library • NaCL/libsodium (C, Ruby, etc) • Keyczar (Python and Java) @jtdowney 17

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@jtdowney 18

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Random Number Generation @jtdowney 19

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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 20

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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 23

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MD_Update(&m,buf,j); @jtdowney 26

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Don't add uninitialised data to the random number generator. This stop valgrind from giving error messages in unrelated code. (Closes: #363516) @jtdowney 27

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/* 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

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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 33

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@jtdowney 34

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Recommendations • Use a cryptographically strong random number generator • Unix-like • Read from /dev/urandom • Windows • RandomNumberGenerator in System.Security.Cryptography (.NET) • CryptGenRandom (Windows) @jtdowney 35

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Hash Functions @jtdowney 36

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Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 37

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9EC4C12949A4F31474F299058CE2B22A @jtdowney 42

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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 43

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

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Pitfalls 1. Using weak/old algorithms 2. Misunderstanding checksums 3. Length extension attacks @jtdowney 46

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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 47

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Naive approach tag = sha256(key || value) @jtdowney 48

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Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = sha256(secret + value) @jtdowney 49

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Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1actually make that at $0" signature = sha256(secret + value) @jtdowney 50

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Length Extension Attacks secret = "my-secret-key" value = "buy 10 units at $1" signature = hmac_sha256(secret, value) @jtdowney 51

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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 54

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Ciphers @jtdowney 55

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

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Pitfalls 1. Using old/weak algorithms 2. Using ECB mode for block ciphers 3. Not using authenticated encryption @jtdowney 60

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

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

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World of hurt @jtdowney 70

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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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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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TLS/SSL @jtdowney 73

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

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Hostname verification @jtdowney 78

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

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@jtdowney 81

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

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testssl.sh @jtdowney 83

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

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

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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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Trust @jtdowney 89

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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 90

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@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ 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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Certificate Pinning @jtdowney 93

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

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Quantum Computers @jtdowney 96

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

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

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@jtdowney 101

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

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Matasano Crypto Challenges http://cryptopals.com @jtdowney 103

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Questions John Downey | @jtdowney @jtdowney 104

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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 105