Maciej Treder
July 29, 2020
510

# WT* is JWT

So what the hell is JWT, Jose header, JWKS, and others?

This presentation covers:
- the cryptography basics (symmetric ciphers, asymmetric ciphers, signing, and verifying)
- JWS (JSON Web Signature)
- JWE (JSON Web Encryption)
- JWT (JSON Web Token)
- JWKS (JSON Web Key Set)
- JWT security
- JWT vulnerabilities

July 29, 2020

## Transcript

6. ### Symmetric cipher a b c d e f g h

i j k l m 1 2 3 4 5 6 7 8 9 10 11 12 13 n o p r s t u v w x y z _ 14 15 16 17 18 19 20 21 22 23 24 25 26 I like you 9 26 12 9 11 5 26 24 15 20

8. ### Asymmetric cipher • Private key - used to decrypt the

message • Public key - used to encrypt the message • Keys are generated using the one-way function f(p,q) = p*q where p & q are primes • Keys can be used interchangeably
9. ### RSA key • Select p & q primes • Calculate

n = p*q • Calculate φ = (p-1)*(q-1) • Choose such e, relatively prime to φ gcd(φ,e) == 1 • Compute such d, that (ed-1) modφ=0 • Private key = (n,e) • Public key = (n,d) p=11 q=3 n = 11*3 = 33 φ = (11-1)*(3-1) = 20 e = 3 d=7 (ed-1) mod φ = 0 (3d-1) mod 20 = 0 3d-1 = 20n d = (20n + 1)/3 d = (20*1+1)/3 d = 21/3 public key = (n, e) = (33, 3) private key = (n, d) = (33, 7)
10. ### Asymmetric cipher Mikes public key Mikes private key Kates public

key Kates private key
11. ### Asymmetric cipher c = m^e mod n public key =

(n, e) = (33, 3) private key = (n, d) = (33, 7) a b c d e f g h i j k l m m 2 3 4 5 6 7 8 9 10 11 12 13 14 c 8 27 31 26 18 13 17 3 10 11 12 19 5 n o p r s t u v w x y z _ m 15 16 17 18 19 20 21 22 23 24 25 26 27 c 9 4 29 24 28 14 21 22 23 30 16 20 15 I like you 10 15 19 10 12 18 15 16 4 21 m’ = c^d mod n
12. ### What if…? Mikes public key Mikes private key Kates public

key Kates private key
13. ### Breaking the RSA • Compromising public key gives an attacker

the modulus n • Key sizes - 1024 to 4096 bit (from 2^1024 to 2^4096) • p: 109337661836325758176115170347306682871557999846322234541387456711212734562876700082908433028755212749702453145932 22946129064538358581018615539828479146469 • q: 109106169673491102317237340786149226453370608821417489682098342251389760111799933942998101597369044685540217082898 24396553412180514827996444845438176099727 • 1024 bit modulus: 119294134840169509055527211331255649644606569661527638012067481954943056851150333806315957037715620297305000118628 770846689969112892212245457118060574995989517080042105263427376322274266393116193517839570773505632231596681121927 337473973220312512599061231322250945506260066557538238517575390621262940383913963
14. ### Signing • Write the message • Hash the message •

Encrypt hash with your private key • Combine message with hash • Encrypt message+hash with their public key • I like you • f1d049f7b893bf8601c66045b801d590 • xxx-yyy-zzz • I like you.xxx-yyy-zzz • aaa-bbb-ccc
15. ### Verifying • Receive the message • Decrypt using your private

key • Get original message & encrypted hash • Hash the original message • Decrypt received hash using their public key • Compare hashes • aaa-bbb-ccc • I like you.xxx-yyy-zzz • f1d049f7b893bf8601c66045b801d590 • xxx-yyy-zzz -> f1d049f7b893bf8601c66045b801d590

19. ### Signing • Create a message • Hash the message •

Encrypt hash with private key • Combine message and encrypted hash • From tomorrow everyone in the kingdom must use his le hand to open the door. • F03CF2EF5AFCE429DB88051746F3864B • Vf2Lx/jOUNLoXawCw4disZhrFfqcoNRGDvpG+SbxUX0= • { “message”: “From tomorrow everyone in the kingdom must use his le hand to open door.” “signature”: “Vf2Lx/jOUNLoXawCw4disZhrFfqcoNRGDvpG+SbxUX0=” }
20. ### Verifying • Get the message • Hash the message •

Decrypt the signature • Compare hash with decrypted signature • { “message”: “From tomorrow everyone in the kingdom must use his le hand to open door.” “signature”: “Vf2Lx/jOUNLoXawCw4disZhrFfqcoNRGDvpG+SbxUX0=” } • F03CF2EF5AFCE429DB88051746F3864B • Vf2Lx/jOUNLoXawCw4disZhrFfqcoNRGDvpG+SbxUX0= • F03CF2EF5AFCE429DB88051746F3864B

23. ### JSON Web Signature eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJJIGFtIjoiSlNPTiBXZWIgVG9rZW4if Q.NmTt6oAkllTqmLqR-QqKxIgIsIaZIRIcBjNyhPnGziU • JOSE Header Javascript Object

Signing and Encryption information about token type, encryption algorithm • Payload - message body • Signature - encrypted header and body
24. ### So.. What the **** is JWT? • JWT does not

exist itself • Signed JWT is called JWS (JSON Web Signature) • Encrypted JWT is called JWE (JSON Web Encryption) JWT JWS JWE
25. ### Registered claims { "alg":"HS256", "typ":"JWT" } { "iss": "authorization-service", "sub":

"myself", "aud": "someone", "iat": 1594655553034, "nbf": 1594655553134, "exp": 1594655553234, "jti": 12345 } Algorithm used for signing Token type Issuer Subject (the user) Audience (recipient) Issued at (time at which token was issued) Not before (time before which token is not valid) Expires (time a er which token is not valid) Unique identifier
26. ### Custom claims { “alg":"RS512", "typ":"JWT" } { "name": "Maciej", "surname":

"Treder", "privileges": ["booking_reschedule"], "exp": 1594655553234 } • Public claims - defined at will by those using JWTs. To avoid collisions should be defend in the IANA JSON Web Token Registry • Private claims - custom claims create to share information between parties that agree on using them

28. ### Pre JWT authorization POST /auth userID POST /book POST /changeGate

POST /cancelFlight
29. ### Pre JWT authorization POST /auth userID POST /book POST /changeGate

POST /cancelFlight canChange? canBook? canCancel?
30. ### Pre JWT authorization POST /auth userID POST /book POST /changeGate

POST /cancelFlight

32. ### JWT authorization POST /auth {privs: [“booking”], exp: 12345} POST /book

POST /changeGate POST /cancelFlight
33. ### JWT authorization POST /auth {privs: [“booking”], exp: 12345} POST /book

POST /changeGate POST /cancelFlight
34. ### JWT authorization POST /auth POST /changeGate @PostMapping("/changeGate") public ResponseEntity<Gate> changeGate(

@RequestHeader("jwt-token") Token token, @RequestBody Gate gate ) { DecodedToken decoded = decodeToken(token); if(decoded.hasPrivilege("changeGate") && verifySignature(token)) { changeGate(gate); return this.flightDetails; } throw new AuthorizationFailureException(); } {privs: [“booking”]}

38. ### Further reading • JSON web token validation https://learn.akamai.com/en-us/webhelp/api-gateway/api-gateway-user-guide/ GUID-682D1D3F-4CF2-46F2-B16B-5E0E1E991218.html •

Protecting JavaScript Microservices on Node.js with JSON Web Tokens and Twilio Authy https://www.twilio.com/blog/protecting-javascript-microservices-node-js-json-web-tokens-twilio- authy

40. ### OAuth authenticate access token request resource validate token token valid

return resource authenticate client
41. ### OAuth authenticate access token request resource return resource authenticate client

validate token
42. ### JWKS • What if my key get compromised? • What

if want to rotate keys? • What if I want to invalidate someones access? • JSON Web Key Set • A repository of keys (public, private, symmetric)
43. ### JWKS { "alg":"HS256", "typ":"JWT", "kid":"12", "jku":"https://my-service.com/.well-known/jwks.json" } { "privileges": ["booking_reschedule"]

} NmTt6oAkllTqmLqR-QqKxIgIsIaZIRIc
44. ### JWKS { "keys": [ { "kty": "RSA", "kid": "1", "alg":

"RS256", "use": "sig", "e": "AQAB", "n": "ujZ1fTy2k- xc6Fa3Bfqe1T78Zx_oWBkDS1TNgw8Jbvbzfj5wgK5 _xSK5ikNlkOXvBjrsVOnCCJXTNiHZxMtIfARbz91O-5n cuNah1H6WntWrLmaVfiIMaaKoNjDzScG1cIjPITarEV jDb0GI0eH9BKpFz8LUbVlcy2m7IOKbmDt6yusHsj7z OfjlV55dT1FU- q5bfyLXQyCf7Uy2JJAVEutWLMp3Ld53q9mvW47Lh hXKl5pKKbLARJgkccpQdN0bURiggvYjs2SHmZgh6d Ceap1mki4LB2aX-Z4TB- u8GbLq51HPZSpK71rR0QzZozluS5aLE49ciQ6-5u7K HWBbrQ" } ] } Key type Key ID Algorithm Usage Exponent Modulus
45. ### JWKS Standard attributes: • kty - key type • kid

- key ID • alg - algorithm [HMAC, RSA, …] • use - usage • e - exponent number • m - modulus number Chinese remainder algorithm: • p, q - prime factors • dp - d (mod p-1) • dq - d (mod q-1) • qi - q^-1 (mod p) Certificate: • x5c - x.509 certificate chain • x5t - Thumbprint of the x.509 cert

48. ### JWKS { "alg":"HS256", "typ":"JWT", "kid":"12", "jku":"https://my-service.com/.well-known/jwks.json" } { "privileges": ["change_gate"]

} NmTt6oAkllTqmLqR-QqKxIgIsIaZIRIc

50. ### Data Security • JWS payload is encoded not encrypted •

Never store sensitive data (ie. credit card numbers) in JWS token • If you want to store sensitive data choose JWE
51. ### Unsigned JWT • JWT doesn’t need to be signed •

Do not rely only on the header when you’re validating the token • “alg”: “none”
52. ### Error Responses • Pay attention to what you are providing

in the error response • https://github.com/jwt-dotnet/jwt/issues/ 61
53. ### Weak Key • HS256 (HMAC-SHA256) • Token is signed applying

the SHA256 twice • When attacker obtains a signed token, he can “easily” retrieve the key (ie. by using the HashCat) • According to documentation, use key which has at least same size as the hash output (256 bit for HS256)
54. ### Decoding != Verifying • Decoding is enough only for denying

access (lack of required claim) • Always verify signature if you want grant someone access • Read library documentation, o en verifying process is available as a separate method
55. ### “Time” attack • Applies when signature is verified byte-a er-byte

• Once bytes doesn’t match then access is denied • Attacker may observe the response time and generate next bytes of the signature
56. ### jku • Always verify the URL provided as a jku

claim { "alg":"HS256", "typ":"JWT", "kid":"12", "jku":"https://attacker.com/.well-known/jwks.json" } { "privileges": ["change_gate"] }

58. ### Summary • JWT is o en confused with JWS which

is one of it’s implementations • It’s a way of stateless data exchange • JWS is built of JOSE header, payload and signature • It’s a good place too keep not-sensitive data, which value should be verified • Always follow given algorithm best practices (i.e. pass-phrase/key size) • JWE is a good choice if you want to keep data encrypted
59. ### Resources • JWT.IO https://jwt.io • JSON web token validation https://learn.akamai.com/en-us/webhelp/api-gateway/api-gateway-user-guide/

GUID-682D1D3F-4CF2-46F2-B16B-5E0E1E991218.html • Verify JWT With JSON Web Key Set (JWKS) In API Gateway https://blogs.akamai.com/2019/10/verify-jwt-with-json-web-key-set-jwks-in-api-gateway.html • RFC 7519 - JSON Web Token https://tools.ietf.org/html/rfc7519
60. ### Resources • Building JavaScript Microservices with Node.js https://www.twilio.com/blog/building-javascript-microservices-node-js • Implementing

Eureka and Zuul for Service Discovery and Dynamic Routing in JavaScript Microservices Running on Node.js https://www.twilio.com/blog/eureka-zuul-service-discovery-dynamic-routing-javascript-microservices-node-js • Scaling Node.js JavaScript Microservices on Shared MongoDB Atlas Cloud Persistence Layers https://www.twilio.com/blog/scale-node-js-javascript-microservices-shared-mongodb-atlas • Protecting JavaScript Microservices on Node.js with JSON Web Tokens and Twilio Authy https://www.twilio.com/blog/protecting-javascript-microservices-node-js-json-web-tokens-twilio-authy