Tales From the CryptA Cryptography Primer

Adam Englander, iovation

Who Am I?

What We Will Discuss

Wearegoingtotalkaboutthecommonmethodsandtermsusedforcryptographyinapplicationdevelopment.

Don’t Dwell

Donotfeelashamedbecauseyouaredoinganyofthiswrong.Justfixitmovingforward.

What Is Cryptography?

Cryptography…isthepracticeandstudyoftechniquesforsecurecommunicationinthepresenceofthirdpartiescalledadversaries. Wikipedia

My Definition of Cryptography

Cryptographyobscuresdatainsuchawaythatitisdifficultandcostlytoduplicateorreverse.

What is Good Cryptography?

Goodcryptographyhasahighlevelofentropy.Thatis,thattheencryptedorhasheddatahasalowlevelofpredictability.

Why Is Entropy Important?

Alldatahaspatterns.Ifyourencryptedorhasheddataretainsthosepatterns,itismuchlessdifficultandlesscostlytoduplicateorreverse.

Example of Poor Entropy

How To Increase Entropy•IncreaseentropybymixingincryptographicallysecurepseudorandomdataintheformofaniniFalizaFonvector(IV)orsalt

•Increaseentropywithfeedbackloops

Feedback Loop Example

Example of Good Entropy

Localized vs Global Entropy

• Highentropyonanitemisgood

• HighentropyacrossthedatasetisbeLer

• PaLernsexistacrossyourenFredatasetthatmayaidadversaries

Cryptography Types

• SymmetricKeyCryptographyusessharedsecrets

• AsymmetricKeyCryptographyusesprivate/publickeypairs

Cryptography Applications

• EncrypFon

• DigitalSignatures

• KeyDerivaFon

Encryption

• ProtecFngdatathatneedstoberecalled

• CanbereversedviadecrypFon

Digital Signature

• UsedtoverifyauthenFcityofdata

• Usedmostlyfordatatransfer

• CannotbereversedbutcanbereproducedforverificaFon

Key Derivation

• A.K.A.passwordhashing

• Cannotbereversed

• ComputaFonallyexpensivebydesign

Symmetric Key Cryptography

Symmetric Key Cryptography

• Sharedsecrets

• Usescipheralgorithmsagainstblocksorstreamsofdata

• MostimplementaFonswilluseblock

Block Cipher Modes

• DO NOT USE Electronic Cookbook (ECB)!!!

• Cipher Block Chaining (CBC) will be the right choice for most implementations

Cipher Block Chaining (CBC)

• EnFremessageisrequiredfordecrypFon

• Fullciphertextblockisusedastheseedforthenextblock

Cipher Block Chaining (CBC)

Digital Signatures (HMAC)• Hash-basedMessageAuthenFcaFonCode(HMAC)

• Hashingcombinedwithkey

• SHA-256orbeLerispreferredtoensureuniqueness

Asymmetric Key Cryptography

Asymmetric Key Cryptography• RSAiscommonandavailable

• Usesverylargeprimeintegers

• VerycomputaFonallyexpensive

• Useskeypairstoprotectsecret

Private/Public Key Pair

• Private key can do encrypt, decrypt, sign, and verify signature

• Public key does not have enough data to decrypt or sign. Can only encrypt and verify signature

Key Size and Hash Algorithm

• Currentminimumrecommendkeysizeis2048

• SHA1isconsideredsafebutSHA-256isbeLer

Data Limitations• RSAcanonlyencryptorsigndatauptothelengthofthekeysize

• Signaturesusehashing

• Cryptoo_enmixedwithsymmetrickeycryptography

Padding• PaddingishowRSAcreatesaddiFonalentropy

• RSA_PKCS1_OAEP_PADDINGisdefaultandshouldalwaysbeused

• RSA_PKCS1_PADDINGisnotsafe

Key Derivation Functions a.k.a Password Hashing

Password Hashing

NEVERusestandardhashingfunc6onlikeMD5orSHA!

Onlyusekeyderiva6onfunc6ons!

Key Derivation• Iterates to increase cost• Iterates to increase cost• Can create cost via threads and

memory• Bigger is better!

Which KDF Should I Use• argon2iisthenewhotness

• scryptispreferred

• bcryptisacceptable

• pbkdf2canbeusedinapinch

• Nopasswordsarebest

Recommendations

Types• UseRSAasymmetrickeycryptographywhentransferringdataandAES/CBCotherwise

• MixwithAESandrandomkeys/IVspertransfer

• Usecrypto.randomBytesforrandomness

• Usebcrypt/scrypt/argon2iforpasswords

Strength

• AES:aes-256-cbc/sha256

• RSA:2048+PKCS1_OAEP/RSA-SHA256

• HashunFlithurts!