Being Boring: A Survivor's Guide to Ruby Cryptography

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@bascule TONY ARCIERI

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How hard could it be? I JUST WANT TO ENCRYPT SOMETHING

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HARD!

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HOW HARD?

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You Will Learn! TODAY

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TODAY Attacks

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Authenticated Encryption HOWTO TODAY Attacks

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Authenticated Encryption HOWTO TODAY Attacks Avoiding The Problem By Letting Cryptographers Do The Hard Work For Us

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RUBY OPENSSL

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How does it work??? CRYPTO

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MAGIC

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MAGIC

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MATH

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SYMMETRIC MSG

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SYMMETRIC

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SYMMETRIC MSG

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ASYMMETRIC MSG

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ASYMMETRIC

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ASYMMETRIC MSG

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MATH + SECURITY

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MATH + PROGRAMMING

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MATH + BUGS

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“Most codes were designed by dilettantes and amateurs with no grasp of the underlying mathematics. It really is quite pitiable.” ! —Neal Stephenson, Cryptonomicon

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SYMMETRIC

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AES

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AES It’s great!*

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AES It’s great!* *WARNING: Read all instructions before proceeding

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AES Plaintext AES Block Cipher 16-byte block Key 16/24/32-bytes (Random) Ciphertext 16-byte block

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HOW TO ENCRYPT >16 bytes?

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PHP Use Rijndael!

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RIJNDAEL-256 Plaintext Rijndael Block Cipher 32-byte block Key 16/24/32-bytes (Random) Ciphertext 32-byte block

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HOW TO ENCRYPT >16 bytes?

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NAIVE SOLUTION

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ECB MODE

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ECB MODE Key 16/24/32-bytes (Random) Plaintext ECB 16-byte block Ciphertext 16-byte block Plaintext ECB 16-byte block Ciphertext 16-byte block Plaintext ECB 16-byte block Ciphertext 16-byte block Plaintext ECB 16-byte block Ciphertext 16-byte block

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PROBLEM

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PROBLEM ECB MODE LEAKS INFORMATION

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SOLUTION

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SOLUTION BLOCK CIPHER MODES OF OPERATION

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CBC CFB OFB CTR

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CBC CFB OFB CTR

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CTR MODE Key 16/24/32-bytes (Random) Counter 1 AES Random Pad 16-byte block Counter 2 AES Random Pad 16-byte block Counter 3 AES Random Pad 16-byte block Counter 4 AES Random Pad 16-byte block ⊕ ⊕ ⊕ ⊕ ⊕ Plaintext 16-byte block Plaintext 16-byte block Plaintext 16-byte block Plaintext 16-byte block Ciphertext 16-byte block Ciphertext 16-byte block Ciphertext 16-byte block Ciphertext 16-byte block Nonce 16-bytes (Random)

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SUCCESS! CONFIDENTIALITY

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PROBLEM

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PROBLEM REPEATING NONCES WILL LEAK INFORMATION

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SOLUTION

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SOLUTION DON’T DO THAT

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PROBLEM

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PROBLEM SUPPORT FOR CTR MODE IN RUBY OPENSSL IS SPOTTY

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SOLUTION

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SOLUTION USE CBC MODE

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PROBLEM

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PROBLEM ATTACKERS CAN CHANGE ENCRYPTED MESSAGES

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PROBLEM MALLEABILITY

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ATTACK AT DAWN CIPHERTEXT

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ATTACK AT DAWN CIPHERTEXT ⊕ DAWN ⊕ DUSK CIPHERTEXT CHANGE

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ATTACK AT DAWN CIPHERTEXT ⊕ DAWN ⊕ DUSK CIPHERTEXT CHANGE ATTACK AT DUSK

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SOLUTION USE A MESSAGE AUTHENTICATION CODE (MAC)

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SOLUTION AUTHENTICATED ENCRYPTION

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MAC Message MAC Function Arbitrary length Key 16/32-bytes (Random) MAC “tag” 32-bytes (or more)

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CMAC GMAC UMAC HMAC

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CMAC GMAC UMAC HMAC

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PROBLEM

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PROBLEM WHAT ORDER DO WE ENCRYPT/MAC?

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MAC-THEN-ENCRYPT PLAINTEXT CIPHERTEXT MAC Used by SSL/TLS

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ENCRYPT-THEN-MAC PLAINTEXT CIPHERTEXT MAC Used by IPSEC

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ENCRYPT-AND-MAC PLAINTEXT CIPHERTEXT MAC Used by SSH

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WHICH ONE GOT IT RIGHT?

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ENCRYPT-THEN-MAC PLAINTEXT CIPHERTEXT MAC Used by IPSEC

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WHY?

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MAC-THEN-ENCRYPT Used by SSL/TLS BEAST PADDING ORACLE

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ENCRYPT-AND-MAC Used by SSH CHOSEN CIPHERTEXT ATTACKS

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REVIEW • AES-CBC! • Encrypt-Then-MAC! • HMAC

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WHAT ELSE COULD GO WRONG?

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TIMING ATTACKS

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PROBLEM THIS IS ALREADY GETTING CRAZY…

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PROBLEM …AND WE HAVEN’T EVEN TALKED ABOUT PUBLIC KEY CRYPTO!

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HOW CAN WE DO BETTER?

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BE MORE BORING

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NOT BORING Ruby OpenSSL A Bunch Of Crazy Code Written By Amateurs Crypto API

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BORING Crypto Library Written By Cryptographers Crypto API

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RbNaCl Ruby binding to the Networking and Cryptography Library by djb https://github.com/cryptosphere/rbnacl

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https://github.com/jedisct1/libsodium

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NaCl PRIMITIVES • Symmetric: SecretBox! • Asymmetric: Box! • And more!

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SYMMETRIC MSG SECRETBOX

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SecretBox • Cipher: XSalsa20! • MAC: Poly1305

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WTF is XSalsa20? THAT’S NOT BORING!

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BORING!

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NOT BORING!

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ASYMMETRIC MSG BOX

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Box • Difﬁe-Hellman: Curve25519! • Cipher: XSalsa20! • MAC: Poly1305

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DIFFIE-HELLMAN PUBLIC PRIVATE PRIVATE PUBLIC + + = = SHARED SECRET SHARED SECRET

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THAT’S ALL FOLKS!

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THAT’S ALL FOLKS! KEEP IT BORING!

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LINKS • RbNaCl: https://github.com/cryptosphere/rbnacl! • NaCl: http://nacl.cr.yp.to! • Libsodium: https://github.com! • Twitter: @bascule